Obesity

Definition

Obesity is an abnormal accumulation of body fat, usually 20% or more over an individual's ideal body weight. Obesity is associated with increased risk of illness, disability, and death.

The branch of medicine that deals with the study and treatment of obesity is known as bariatrics. As obesity has become a major health problem in the United States, bariatrics has become a separate medical and surgical specialty.

Description

Obesity traditionally has been defined as a weight at least 20% above the weight corresponding to the lowest death rate for individuals of a specific height, gender, and age (ideal weight). Twenty to forty percent over ideal weight is considered mildly obese; 40-100% over ideal weight is considered moderately obese; and 100% over ideal weight is considered severely, or morbidly, obese. More recent guidelines for obesity use a measurement called BMI (body mass index) which is the individual's weight multiplied by 703 and then divided by twice the height in inches. BMI of 25.9-29 is considered overweight; BMI over 30 is considered obese. Measurements and comparisons of waist and hip circumference can also provide some information regarding risk factors associated with weight. The higher the ratio, the greater the chance for weight-associated complications. Calipers can be used to measure skin-fold thickness to determine whether tissue is muscle (lean) or adipose tissue (fat).

Much concern has been generated about the increasing incidence of obesity among Americans. Some studies have noted an increase from 12% to 18% occurring between 1991 and 1998. Other studies have actually estimated that a full 50% of all Americans are overweight. The World Health Organization terms obesity a worldwide epidemic, and the diseases which can occur due to obesity are becoming increasingly prevalent.

Excessive weight can result in many serious, potentially life-threatening health problems, including hypertension, Type II diabetes mellitus (non-insulin dependent diabetes), increased risk for coronary disease, increased unexplained heart attack, hyperlipidemia, infertility, and a higher prevalence of colon, prostate, endometrial, and, possibly, breast cancer. Approximately 300,000 deaths a year are attributed to obesity, prompting leaders in public health, such as former Surgeon General C. Everett Koop, M.D., to label obesity "the second leading cause of preventable deaths in the United States."

Causes and symptoms

The mechanism for excessive weight gain is clear—more calories are consumed than the body burns, and the excess calories are stored as fat (adipose) tissue. However, the exact cause is not as clear and likely arises from a complex combination of factors. Genetic factors significantly influence how the body regulates the appetite and the rate at which it turns food into energy (metabolic rate). Studies of adoptees confirm this relationship—the majority of adoptees followed a pattern of weight gain that more closely resembled that of their birth parents than their adoptive parents. A genetic predisposition to weight gain, however, does not automatically mean that a person will be obese. Eating habits and patterns of physical activity also play a significant role in the amount of weight a person gains. Recent studies have indicated that the amount of fat in a person's diet may have a greater impact on weight than the number of calories it contains. Carbohydrates like cereals, breads, fruits, and vegetables and protein (fish, lean meat, turkey breast, skim milk) are converted to fuel almost as soon as they are consumed. Most fat calories are immediately stored in fat cells, which add to the body's weight and girth as they expand and multiply. A sedentary lifestyle, particularly prevalent in affluent societies, such as in the United States, can contribute to weight gain. Psychological factors, such as depression and low self-esteem may, in some cases, also play a role in weight gain.

At what stage of life a person becomes obese can affect his or her ability to lose weight. In childhood, excess calories are converted into new fat cells (hyperplastic obesity), while excess calories consumed in adulthood only serve to expand existing fat cells (hypertrophic obesity). Since dieting and exercise can only reduce the size of fat cells, not eliminate them, persons who were obese as children can have great difficulty losing weight, since they may have up to five times as many fat cells as someone who became overweight as an adult.

Obesity can also be a side effect of certain disorders and conditions, including:

• Cushing's syndrome, a disorder involving the excessive release of the hormone cortisol
• hypothyroidism, a condition caused by an underactive thyroid gland
• neurologic disturbances, such as damage to the hypothalamus, a structure located deep within the brain that helps regulate appetite
• consumption of such drugs as steroids, antipsychotic medications, or antidepressants

The major symptoms of obesity are excessive weight gain and the presence of large amounts of fatty tissue. Obesity can also give rise to several secondary conditions, including:

• arthritis and other orthopedic problems, such as lower back pain
• hernias
• heartburn
• adult-onset asthma
• gum disease
• high cholesterol levels
• gallstones
• high blood pressure
• menstrual irregularities or cessation of menstruation (amenorhhea)
• decreased fertility, and pregnancy complications
• shortness of breath that can be incapacitating
• sleep apnea and sleeping disorders
• skin disorders arising from the bacterial breakdown of sweat and cellular material in thick folds of skin or from increased friction between folds
• emotional and social problems

Diagnosis

Diagnosis of obesity is made by observation and by comparing the patient's weight to ideal weight charts. Many doctors and obesity researchers refer to the body mass index (BMI), which uses a height-weight relationship to calculate an individual's ideal weight and personal risk of developing obesity-related health problems. Physicians may also obtain direct measurements of an individual's body fat content by using calipers to measure skin-fold thickness at the back of the upper arm and other sites. The most accurate means of measuring body fat content involves immersing a person in water and measuring relative displacement; however, this method is very impractical and is usually only used in scientific studies requiring very specific assessments. Women whose body fat exceeds 30% and men whose body fat exceeds 25% are generally considered obese.

Doctors may also note how a person carries excess weight on his or her body. Studies have shown that this factor may indicate whether or not an individual has a predisposition to develop certain diseases or conditions that may accompany obesity. "Apple-shaped" individuals who store most of their weight around the waist and abdomen are at greater risk for cancer, heart disease, stroke, and diabetes than "pear-shaped" people whose extra pounds settle primarily in their hips and thighs.

Treatment

Treatment of obesity depends primarily on how overweight a person is and his or her overall health. However, to be successful, any treatment must affect life-long behavioral changes rather than short-term weight loss. "Yo-yo" dieting, in which weight is repeatedly lost and regained, has been shown to increase a person's likelihood of developing fatal health problems than if the weight had been lost gradually or not lost at all. Behavior-focused treatment should concentrate on:

• What and how much a person eats. This aspect may involve keeping a food diary and developing a better understanding of the nutritional value and fat content of foods. It may also involve changing grocery-shopping habits (e.g., buying only what is on a prepared list and only going on a certain day), timing of meals (to prevent feelings of hunger, a person may plan frequent, small meals), and actually slowing down the rate at which a person eats.
• How a person responds to food. This may involve understanding what psychological issues underlie a person's eating habits. For example, one person may binge eat when under stress, while another may always use food as a reward. In recognizing these psychological triggers, an individual can develop alternate coping mechanisms that do not focus on food.
• How they spend their time. Making activity and exercise an integrated part of everyday life is a key to achieving and maintaining weight loss. Starting slowly and building endurance keeps individuals from becoming discouraged. Varying routines and trying new activities also keeps interest high.

For most individuals who are mildly obese, these behavior modifications entail life-style changes they can make independently while being supervised by a family physician. Other mildly obese persons may seek the help of a commercial weight-loss program (e.g., Weight Watchers). The effectiveness of these programs is difficult to assess, since programs vary widely, drop-out rates are high, and few employ members of the medical community. However, programs that emphasize realistic goals, gradual progress, sensible eating, and exercise can be very helpful and are recommended by many doctors. Programs that promise instant weight loss or feature severely restricted diets are not effective and, in some cases, can be dangerous.

For individuals who are moderately obese, medically supervised behavior modification and weight loss are required. While doctors will put most moderately obese patients on a balanced, low-calorie diet (1200-1500 calories a day), they may recommend that certain individuals follow a very-low-calorie liquid protein diet (400-700 calories) for as long as three months. This therapy, however, should not be confused with commercial liquid protein diets or commercial weight-loss shakes and drinks. Doctors tailor these diets to specific patients, monitor patients carefully, and use them for only a short period of time. In addition to reducing the amount and type of calories consumed by the patient, doctors will recommend professional therapists or psychiatrists who can help the individual effectively change his or her behavior in regard to eating.

For individuals who are severely obese, dietary changes and behavior modification may be accompanied by surgery to reduce or bypass portions of the stomach or small intestine. Although obesity surgery is less risky as of 2003 because of recent innovations in equipment and surgical technique, it is still performed only on patients for whom other strategies have failed and whose obesity seriously threatens their health. Other surgical procedures are not recommended, including liposuction, a purely cosmetic procedure in which a suction device is used to remove fat from beneath the skin, and jaw wiring, which can damage gums and teeth and cause painful muscle spasms.

Appetite-suppressant drugs are sometimes prescribed to aid in weight loss. These drugs work by increasing levels of serotonin or catecholamine, which are brain chemicals that control feelings of fullness. Appetite suppressants, though, are not considered truly effective, since most of the weight lost while taking them is usually regained after stopping them. Also, suppressants containing amphetamines can be potentially abused by patients. While most of the immediate side-effects of these drugs are harmless, the long-term effects of these drugs, in many cases, are unknown. Two drugs, dexfenfluramine hydrochloride (Redux) and fenfluramine (Pondimin) as well as a combination fenfluramine-phentermine (Fen/Phen) drug, were taken off the market when they were shown to cause potentially fatal heart defects. In November 1997, the United States Food and Drug Administration (FDA) approved a new weight-loss drug, sibutramine (Meridia). Available only with a doctor's prescription, Meridia can significantly elevate blood pressure and cause dry mouth, headache, constipation, and insomnia. This medication should not be used by patients with a history of congestive heart failure, heart disease, stroke, or uncontrolled high blood pressure.

Other weight-loss medications available with a doctor's prescription include:

• diethylpropion (Tenuate, Tenuate dospan)
• mazindol (Mazanor, Sanorex)
• phendimetrazine (Bontril, Plegine, Prelu-2, X-Trozine)
• phentermine (Adipex-P, Fastin, Ionamin, Oby-trim)

Phenylpropanolamine (Acutrim, Dextarim) is the only nonprescription weight-loss drug approved by the FDA These over-the-counter diet aids can boost weight loss by 5%. Combined with diet and exercise and used only with a doctor's approval, prescription anti-obesity medications enable some patients to lose 10% more weight than they otherwise would. Most patients regain lost weight after discontinuing use of either prescription medications or nonprescription weight-loss products.

Prescription medications or over-the-counter weight-loss products can cause:

• constipation
• dry mouth
• headache
• irritability
• nausea
• nervousness
• sweating

None of them should be used by patients taking monoamine oxidase inhibitors (MAO inhibitors).

Doctors sometimes prescribe fluoxetine (Prozac), an antidepressant that can increase weight loss by about 10%. Weight loss may be temporary and side effects of this medication include diarrhea, fatigue, insomnia, nausea, and thirst. Weight-loss drugs currently being developed or tested include ones that can prevent fat absorption or digestion; reduce the desire for food and prompt the body to burn calories more quickly; and regulate the activity of substances that control eating habits and stimulate overeating.

Alternative treatment

The Chinese herb ephedra (Ephedra sinica ), combined with caffeine, exercise, and a low-fat diet in physician-supervised weight-loss programs, can cause at least a temporary increase in weight loss. However, the large doses of ephedra required to achieve the desired result can also cause:

• anxiety
• heart arrhythmias
• heart attack
• high blood pressure
• insomnia
• irritability
• nervousness
• seizures
• strokes
• death

Ephedra should not be used by anyone with a history of diabetes, heart disease, or thyroid problems. In fact, an article that appeared in the Journal of the American Medical Association in early 2003 advised against the use of ephedra.

Diuretic herbs, which increase urine production, can cause short-term weight loss but cannot help patients achieve lasting weight control. The body responds to heightened urine output by increasing thirst to replace lost fluids, and patients who use diuretics for an extended period of time eventually start retaining water again anyway. In moderate doses, psyllium, a mucilaginous herb available in bulk-forming laxatives like Metamucil, absorbs fluid and makes patients feel as if they have eaten enough. Red peppers and mustard help patients lose weight more quickly by accelerating the metabolic rate. They also make people more thirsty, so they crave water instead of food. Walnuts contain serotonin, the brain chemical that tells the body it has eaten enough. Dandelion (Taraxacum officinale ) can raise metabolism and counter a desire for sugary foods.

Acupressure and acupuncture can also suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that enhances the patient's determination to lose weight. By improving physical strength, mental concentration, and emotional serenity, yoga can provide the same benefits. Also, patients who play soft, slow music during meals often find that they eat less food but enjoy it more.

Getting the correct ratios of protein, carbohydrates, and good-quality fats can help in weight loss via enhancement of the metabolism. Support groups that are informed about healthy, nutritious, and balanced diets can offer an individual the support he or she needs to maintain this type of eating regimen.

Prognosis

As many as 85% of dieters who do not exercise on a regular basis regain their lost weight within two years. In five years, the figure rises to 90%. Repeatedly losing and regaining weight (yo yo dieting) encourages the body to store fat and may increase a patient's risk of developing heart disease. The primary factor in achieving and maintaining weight loss is a life-long commitment to regular exercise and sensible eating habits.

Prevention

Obesity experts suggest that a key to preventing excess weight gain is monitoring fat consumption rather than counting calories, and the National Cholesterol Education Program maintains that only 30% of calories should be derived from fat. Only one-third of those calories should be contained in saturated fats (the kind of fat found in high concentrations in meat, poultry, and dairy products). Because most people eat more than they think they do, keeping a detailed food diary is a useful way to assess eating habits. Eating three balanced, moderate-portion meals a day—with the main meal at mid-day—is a more effective way to prevent obesity than fasting or crash diets. Exercise increases the metabolic rate by creating muscle, which burns more calories than fat. When regular exercise is combined with regular, healthful meals, calories continue to burn at an accelerated rate for several hours. Finally, encouraging healthful habits in children is a key to preventing childhood obesity and the health problems that follow in adulthood.

New directions in obesity treatment

The rapid rise in the incidence of obesity in the United States since 1990 has prompted researchers to look for new treatments. One approach involves the application of antidiabetes drugs to the treatment of obesity. Metformin (Glucophage), a drug that was approved by the Food and Dug Administration (FDA) in 1994 for the treatment of type 2 diabetes, shows promise in treating obesity associated with insulin resistance.

Another field of obesity research is the study of hormones, particularly leptin, which is produced by fat cells in the body, and ghrelin, which is secreted by cells in the lining of the stomach. Both hormones are known to affect appetite and the body's energy balance. Leptin is also related to reproductive function, while ghrelin stimulates the pituitary gland to release growth hormone. Further studies of these two hormones may lead to the development of new medications to control appetite and food intake.

KEY TERMS

Adipose tissue— Fat tissue.

Appetite suppressant— Drug that decreases feelings of hunger. Most work by increasing levels of serotonin or catecholamine, chemicals in the brain that control appetite.

Bariatrics— The branch of medicine that deals with the prevention and treatment of obesity and related disorders.

Ghrelin— A recently discovered peptide hormone secreted by cells in the lining of the stomach. Ghrelin is important in appetite regulation and maintaining the body's energy balance.

Hyperlipidemia— Abnormally high levels of lipids in blood plasma.

Hyperplastic obesity— Excessive weight gain in childhood, characterized by the creation of new fat cells.

Hypertension— High blood pressure.

Hypertrophic obesity— Excessive weight gain in adulthood, characterized by expansion of already existing fat cells.

Ideal weight— Weight corresponding to the lowest death rate for individuals of a specific height, gender, and age.

Leptin— A protein hormone that affects feeding behavior and hunger in humans. At present it is thought that obesity in humans may result in part from insensitivity to leptin.

A third approach to obesity treatment involves research into the social factors that encourage or reinforce weight gain in humans. Researchers are looking at such issues as the advertising and marketing of food products; media stereotypes of obesity; the development of eating disorders in adolescents and adults; and similar questions.

Resources

BOOKS

Beers, Mark H., MD, and Robert Berkow, MD, editors. "Nutritional Disorders: Obesity." Section 1, Chapter 5. In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.

Flancbaum, Louis, MD, with Erica Manfred and Deborah Biskin. The Doctor's Guide to Weight Loss Surgery. West Hurley, NY: Fredonia Communications, 2001.

Pi-Sunyer, F. Xavier. "Obesity." In Cecil Textbook of Medicine, edited by Russel L. Cecil, et al. Philadelphia, PA: W. B. Saunders Company, 2000.

PERIODICALS

Aronne, L. J., and K. R. Segal. "Weight Gain in the Treatment of Mood Disorders." Journal of Clinical Psychiatry 64, Supplement 8 (2003): 22-29.

Bell, S. J., and G. K. Goodrick. "A Functional Food Product for the Management of Weight." Critical Reviews in Food Science and Nutrition 42 (March 2002): 163-178.

Brudnak, M. A. "Weight-Loss Drugs and Supplements: Are There Safer Alternatives?" Medical Hypotheses 58 (January 2002): 28-33.

Colquitt, J., A. Clegg, M. Sidhu, and P. Royle. "Surgery for Morbid Obesity." Cochrane Database Systems Review 2003: CD003641.

Espelund, U., T. K. Hansen, H. Orskov, and J. Frystyk. "Assessment of Ghrelin." APMIS Supplementum 109 (2003): 140-145.

Hundal, R. S., and S. E. Inzucchi. "Metformin: New Understandings, New Uses." Drugs 63 (2003): 1879-1894.

Pirozzo, S., C. Summerbell, C. Cameron, and P. Glasziou. "Advice on Low-Fat Diets for Obesity (Cochrane Review)." Cochrane Database Systems Review 2002: CD003640.

Schurgin, S., and R. D. Siegel. "Pharmacotherapy of Obesity: An Update." Nutrition in Clinical Care 6 (January-April 2003): 27-37.

Shekelle, P. G., M. L. Hardy, S. C. Morton, et al. "Efficacy and Safety of Ephedra and Ephedrine for Weight Loss and Athletic Performance: A Meta-Analysis." Journal of the American Medical Association 289 (March 26, 2003): 1537-1545.

Tataranni, P. A. "Treatment of Obesity: Should We Target the Individual or Society?" Current Pharmaceutical Design 9 (2003): 1151-1163.

Veniant, M. M., and C. P. LeBel. "Leptin: From Animals to Humans." Current Pharmaceutical Design 9 (2003): 811-818.

ORGANIZATIONS

American Dietetic Association. (800) 877-1600. 〈www.eatright.org.〉.

American Obesity Association (AOA). 1250 24th Street NW, Suite 300, Washington, DC 20037. (202) 776-7711 or (800) 98-OBESE. 〈www.obesity.org〉.

American Society for Bariatric Surgery. 7328 West University Avenue, Suite F, Gainesville, FL 32607. (352) 331-4900. 〈www.asbs.org〉.

American Society of Bariatric Physicians. 5453 East Evans Place, Denver, CO 80222-5234. (303) 770-2526. 〈www.asbp.org〉.

HCF Nutrition Research Foundation, Inc. P.O. Box 22124, Lexington, KY 40522. (606) 276-3119.

National Institute of Diabetes and Digestive and Kidney Diseases. 31 Center Drive, USC2560, Building 31, Room 9A-04, Bethesda, MD 20892-2560. (301) 496-3583. 〈www.niddk.nih/gov〉.

National Obesity Research Foundation. Temple University, Weiss Hall 867, Philadelphia, PA 19122.

Weight-Control Information Network. 1 Win Way, Bethesda, MD 20896-3665. (301) 951-1120. 〈www.navigator.tufts.edu/special/win.html〉.

Obesity

Measurements

Widespread weight problem

Genetic, environmental, and societal factors

Health effects

Diets and treatments

Healthy lifestyles

Resources

Obesity is a condition where the body of mammals, such as humans, have stored so much natural energy reserves that the fatty tissues they are stored in have expanded to a point where it is medically considered a significant health risk, with a possible increased rate of mortality to that body. Obesity is also considered generally as any weight that is at least 20% above a person’s ideal weight. This statistic is further broken down by percentage and degree of obesity: 20 to 40% over ideal weight is considered mildly obese, 40 to 100% over ideal weight is considered moderately obese, and more than 100% over ideal weight is severely (morbidly) obese.

In order to fit the definition of obesity, the excess weight must be due to adipose, or fat, tissue. Muscle mass does not account for the weight attributed to obesity. Therefore, a body-builder with tremendous muscle mass for example is not, by definition, obese. A deleterious condition, obesity is harmful because of the many other health problems associated with it. In fact, even moderate obesity can contribute to additional health problems. The condition has been linked to common but very serious diseases such as high bloodpressure, non-insulin dependent diabetes mellitus, cardiovascular (heart) disease, and arthritis.

A proposed link between obesity and certain kinds of cancer has also been put forth in recent years, making the health risks of weight-gain more evident. According to experts, obesity has reached epidemic proportions within the United States, affecting millions of American citizens. This increase in obesity, and associated illness, is believed to be the result of a modern trend toward elevated daily caloric intake combined with a decrease in physical activity. As many as two-thirds of the American adult population report trying to lose weight or keep weight off. Yet, recent information shows that many Americans do not follow well-established lifestyle guidelines that can accomplish both.

According to the American Heart Association, as of 2004, among U.S. citizens age 20 years and older, 136.5 million are overweight or obese. Of that number, 69.6 million are men and 66.9 million are women. Of the total numbers for overweight and obese people, 64.0 million are considered obese, with 27.9 million being men and 36.1 million being women.

Measurements

Body mass index (BMI) has been the medical standard for obesity measurement since the early 1980s, when government researchers developed it to take height into account in weight measurement. BMI equals a person’s weight in kilograms (kg) divided by that person’s height in meters (m) squared (kg/m²). In June 1998, the U.S. federal government changed its guidelines for BMI, making a BMI of 18.5 to 24.9 a healthy weight/height ratio. (A person with a BMI of less than 18.5 is considered underweight.) In BMI terms, the overweight range is 25.0 to 29.9 for both men and women.

A person is considered obese if their BMI is within 30.0 to 40.0, and considered extremely obese if their BMI is over 40.0. Depending on where a person is positioned within this BMI range—and depending on whether the person’s waist size (waist circumference) is below or above 40 inches (102 centimeters) for men, or below or above 35 inches (89 centimeters) for women—then that person can be at: increased, high, or extremely high risk for health-related problems.

According to these guidelines, a person who is 5 feet (1.52 meters) in height and weighs 155 pounds (70.3 kilograms) has a BMI of 30.3, and is considered obese. Someone who is 5 feet/4 inches (1.62 meters) in height and weighs 155 pounds (70.3 kilograms) has a BMI of 26.7, and is considered overweight, but not obese. A person who is 5 feet/11 inches (1.80 meters) and weighs 155 pounds (70.3 kilograms) is in the healthy BMI range, with a BMI of 21.7.

An accurate, but inconvenient method of estimating body fat uses a blood test. Here, a water-soluble compound that is detectable and measurable in solution is injected into the person. Because the substance

is water soluble, it does not mix well with fat, nor highly fatty tissues such as adipose tissue. After allowing some time for the substance to distribute throughout the body, blood samples are taken. The concentration of the substance in blood then indicates how much it has been diluted in the body. This concentration, then, gives an estimate of lean body tissue. Using this, the amount of fatty tissue can be calculated. Another method is skinfold measurement.

A simpler and less invasive way to determine percent of body fat, this technique uses skinfold calipers. A caliper is an instrument consisting of a pair of movable curved arms that measures the thickness of skin folds at certain body regions. Thicker skinfolds have more fat content, and the amount of fat under skin is thus, correlated with total body fat. A more technologically oriented way of estimating percent body fat uses bioelectrical impedance. By transmitting a small electrical pulse through the body, the amount of body fat can be estimated. Because water conducts electricity more readily than fat, and as lean tissue contains more water than fat, the electrical surge can detect the amount of lean tissue, and thus fat tissue, present.

Widespread weight problem

Excessive weight can result in many serious and potentially deadly health problems, including high blood pressure, diabetes, infertility and increased risk for heart disease and heart attack. In common terms, obese means very overweight and often carries negative connotations. But in weight-control medicine, obese is a non-judgmental term that simply means a certain body mass index.

Obesity is a chronic, metabolic disease caused by multiple and complex inherited and acquired factors. It is a condition that affects millions of Americans and is an increasing worldwide problem. Obesity is also prevalent in Europe, Caribbean nations, China, Japan, Malaysia, Samoa, the Middle East, and other countries. However, estimating the number of obese individuals is difficult because experts cannot agree on an exact definition. The World Health Organization (WHO) recognizes three grades of excess body weight: grade 1 meaning the individual is overweight, while grades 2 and 3 signify obesity. Being overweight is not the same as being obese. A person who is overweight simply weighs more than a statistically calculated target weight given their gender, height, and age.

Recent surveys have determined that approximately 54% of adults, about 11% of adolescents of ages twelve to seventeen years, and more than 14% of children of ages six to eleven years in the United States are over-weight. These staggering figures, while not specifically measuring obesity, point to increases in obesity overall. The problem of obesity has gained much attention because it results in roughly 300,000 preventable deaths in the United States each year, which is surpassed only by the negative health outcomes of tobacco use. Obesity costs are estimated to exceed $100 billion annually and continue to grow with the rate of increase in obese individuals. In the 1990s, the average number of obese individuals (defined as those with body weights 30% or more above their ideal body weight) increased over 6% in adult Americans of ages 18 to 29 years. The greatest change is seen in the southern United States, where a 67% increase in the number of obese individuals was measured between 1991 and 1998. Overall, the proportion of the society that is obese has risen from 25% to over 32%. As of 2005, eight out of ten Americans over 25 years of age are overweight and 78% of Americans do not meet basic activity levels that are recommended by federal health agencies; and, of that percentage, 25% are completely sedentary. It is predicted that by the year 2025, over 40% of the adult U.S. population will be obese.

Genetic, environmental, and societal factors

The physical explanation for weight gain is simple: more calories are consumed than burned by a body. As a result, the body stores the excess calories as fat. However, the exact reasons why some people become obese while others do not is not clear.

Genetic factors influence how the body regulates appetite and the rate at which it turns food into energy (metabolic rate), but a genetic tendency to gain weight does not automatically mean that a person will be obese. Eating habits and patterns of physical activity also are important. While there is a genetic component to weight, no one is destined to be obese. If weight has been a major problem in a family, the obese person may not be able to become as thin as he or she would like, but losing weight is possible.

Recent studies have shown that the amount of fat in a person’s diet may be more important than the number of calories. Carbohydrates like cereals, breads, fruits, and vegetables and protein (fish, lean meat, turkey breast, skim milk) are converted to fuel almost as soon as they are consumed. Most fat calories, however, are immediately stored in fat cells, which add to the body’s weight and girth as they expand and multiply.

Obesity can also be a side-effect of certain disorders and conditions, including an underactive thyroid gland or damage to the part of the brain that helps regulate appetite. Certain medicines, such as steroids and antidepressants, also may cause weight gain.

Obesity is recognized by the National Institutes of Health as a disease in itself, and the medical problems caused by obesity are serious and often life-threatening. In fact, obesity is not just a cosmetic problem—it is a health hazard. Someone who is 40% overweight is twice as likely to die prematurely as an average-weight person after 10 to 30 years of being obese. Obesity has been linked to diabetes, heart disease, high blood pressure, stroke, infertility, snoring, menstrual irregularities, higher rates of certain types of cancer, gallbladder disease and gallstones, osteoarthritis, gout, and breathing problems (including sleep apnea).

The location of fat on a person’s body is one clue to the risk of developing certain obesity-related conditions. Apple-shaped people who store most of their weight around the waist and abdomen are at greater risk for cancer, heart disease, stroke, and diabetes than pear-shaped people whose extra pounds settle primarily in their hips and thighs.

Almost all of these problems are relieved by permanent significant weight loss. But for many obese people, health concerns are less important than the emotional suffering they face at the hands of thinner people. U.S. society and many other industrial societies in the world place great emphasis on physical appearance, and those societies equate attractiveness with slimness, especially in women. Many Americans assume that obese people are gluttonous, lazy, stupid and self-indulgent, and because of these attitudes, obese people face daily prejudice and discrimination at work, at school, while job-hunting, and in social situations. Feelings of rejection, shame, and depression are common.

While it is unacceptable to discriminate against people on the basis of race, religion, gender, sexual persuasion, or ethnic group, many Americans still discriminate against the obese. Overweight people find it more difficult to get and keep a job; almost half those who are 100 pounds (45 kilograms) or more overweight are unemployed. For those who do have jobs, obese workers are often overlooked because they do not present a corporate or professional image. Heavy people are often discriminated against by their insurance carriers when the insurer refuses to provide therapy that will help relieve obesity, ignoring current scientific literature on how surgery can prevent, diminish, and often cure diseases and conditions associated with obesity. Frequently, heavy patients are discriminated against by their doctors, who tell them that their medical problems will disappear if they just stop eating.

The types of disabilities experienced by obese people are not widely acknowledged by society. It is common for heavy people to be discriminated against in social situations, where they are often treated as non-persons. Most people think that obesity is the result of slothful living, poor personal eating and exercise habits, and lack of intelligence and self-control.

Physiological causes

Obesity is a condition that is influenced by genetic and environmental factors (such as energy intake and expenditure, fetal nutrition, culture). There are four major physiological causes of obesity: endocrine disorders (growth hormone deficiency, Cushing syndrome), genetic syndromes (Prader-Willi syndrome or Alstrom syndrome), disorders of the central nervous system (tumor, trauma) or the most common cause, multifactorial or primary obesity (caused by an interaction of multiple genes).

A number of metabolic functions can be affected by genetic background and result in a variable production, storage, and distribution of body fat among different people. Therefore, some people are more susceptible to obesity than others. Although obesity appears to run in families, the twin studies have indicated that only 50% of the tendency for obesity is inherited, the rest is contributed by the environment.

Although at present, environmental factors responsible for the weight imbalance are obscure, an imbalance between energy intake (diet) and energy output (exercise and energy demands of the body) appears as a main problem resulting in surplus body fat. Energy output is related to the level of physical activity undertaken by a person. People engaging in regular exercise are likely to loose or not gain weight over time, while a reduction in physical activity brought about by an increase in inactive lifestyle (television watching, computer games, etc.) leads to weight gain. The changes in lifestyle affect energy intake. An increase in consumption of fat and sugar-containing foods results in overeating, as those foods have poor satiating capacity. It is clear that the combination of bad dietary habits and low exercise levels increases the risk of obesity and related diseases. This risk is increased in people with lower metabolic rates. Metabolism, defined as the sum total of all the chemical reactions occurring within the cells of the body, can be affected by thyroid hormone levels, growth hormone levels, and insulin levels. Some researchers suspect that imbalances in these hormones can cause obesity. An important cause can also be a malfunction in the hypothalamus region of the brain that regulates appetite and satiety. Satiety is a feeling of satisfaction after eating. If the hypothalamus malfunctions, an individual may not experience feelings of fullness after eating, and overeat as a result of feeling constantly hungry. Moreover, it appears that fetal development and nutrition can have an influence on development of obesity later in life. It has been suggested that maternal malnutrition leads not only to low birth weight, but also to an increased risk of developing obesity postnatally.

Health effects

Two leading causes of death and disability among adults are heart disease and stroke. People who are over-weight are more likely to have elevated blood pressure, or hypertension, which is a major risk factor for both stroke and chronic congestive heart failure. Also, high blood levels of cholesterol and triglycerides (fats) can lead to heart disease. Often, raised levels of cholesterol and triglycerides are linked to being overweight. Obesity can also lead to angina (chest pain) from decreased oxygen to the heart. Fortunately, the loss of a relatively small amount of weight can make a dramatic difference. A reduction of 10% of body weight can decrease the chances of heart disease in obese individuals.

Another major disease, affecting millions of people, that is linked to obesity is diabetes. Diabetes mellitus is a disease caused by an inability of the body to metabolise carbohydrates and control blood sugar levels. Some people, having type I diabetes mellitus, are born with the disease. Type II, or non-insulin dependent diabetes mellitus, is acquired over time, but can be serious nonetheless. Both kinds of diabetes are a major cause of heart disease, stroke, kidney disease, blindness, and early death. People who are obese are much more likely to develop type II diabetes.

Several kinds of cancer have been linked to obesity and excess body fat. Obese males are at greater risk of developing colon cancer, rectal cancer, and prostate cancer. Women who are obese are at greater risk of developing cervical cancer, ovarian cancer, and breast cancer. Exact mechanisms are, by and large, unknown. For some types of cancer, it is not known whether the increase in risk is due to obesity itself or a high fat, high calorie diet.

Other serious diseases, like sleep apnea, gout, and osteoarthritis are also linked to obesity. Sleep apnea is characterized by short periods of time where breathing stops during sleep. The risk for sleep apnea increases with increasing body weight. Osteoarthritis is a painful degenerative joint disorder that has been called wear-and-tear arthritis since it is caused by physical stress on joints. It most often affects knees, hips, and lower back vertebrae. Extra weight can place pressure on these joints, accelerating the wearing away of the cartilage that normally protects them. Gout is a joint disease, but it is caused by high levels of uric acid. Uric acid can form crystal deposits in the joints, causing pain and inflammation. Gout is more common in obese people.

All of the diseases listed above become exaggerated in people who display morbid obesity. Morbid obesity is defined as a body weight that is twice the ideal value. Morbidly obese individuals are at greater risk of developing serious health problems. Fortunately, obesity can be managed and a reduction in weight can produce reductions in associated disease. Long-term changes in eating habits and physical activity are listed as the best ways to lose weight and keep it off over time.

Diets and treatments

Most weight-loss diets do not work because they are poorly designed and they do not help people keep the weight off. In fact, any diet that emphasizes limiting calories for a set period of time, or that focuses on crash dieting, will fail. The person may lose weight temporarily but as soon as the diet stops, the pounds return. To lose weight and keep it off, an obese person must change eating habits permanently and get more exercise.

An obese person who wants to lose weight should not focus on dieting, because dieting means deprivation, and no one chooses to remain deprived for long. Losing weight by dieting alone will weaken muscles, lower energy levels, and increase fatigue. Dropping weight too quickly can lessen muscle mass, which can be harmful. The best plan is to try to lose about one pound (about one-half kilogram) a week so that the loss will not harm the body. This loss should be linked to a realistic exercise program to burn fat, build muscle and increase cardiovascular fitness.

The success rate for dieting is approximately 3 to 5%. There are a wide variety of weight-loss programs available. Do-it-yourself programs include individual efforts and groups of like-minded people such as Overeaters Anonymous and TOPS (Take Off Pounds Sensibly).

Non-clinical programs are commercial franchises that offer program materials that may or may not be produced with guidance from health care providers. These programs rely heavily on counselors (who are typically not health care providers) to provide services to clients.

Clinical programs are provided by a licensed professional who may or may not have had the specialized training to treat obese patients. Clinical programs include such services as nutrition, medical care, behavior therapy, exercise and psychological counseling, and may use very-low-calorie diets, medications, and surgery. The medication and surgery clinical programs offer help to overweight individuals who have not been able to lose weight with other approaches.

For people who are severely obese, diet and lifestyle changes may be accompanied by surgery to reduce or bypass portions of the stomach or small intestine. Because such surgery can be risky, it is done only after other weight-loss strategies have failed, and only on patients whose obesity seriously threatens their health. Patients who have had some variety of stomach bypass or stapling maintain a weight loss of at least 60% at the end of five years.

However, weight loss after surgery is not guaranteed and depends on how effectively the patient follows the recommended program.

Other surgical procedures, such as liposuction and jaw wiring, are not recommended for obese patients.

Appetite-suppressant drugs are sometimes prescribed to help people lose weight. These drugs work by increasing levels of brain chemicals that control feelings of fullness and satisfaction. However, most of the weight lost while taking appetite suppressants is usually regained after stopping them. Also, suppressants containing amphetamines can be abused by patients. Two weight-loss drugs, dexfenfluramine hydrochloride (Redux^®) and fenfluramine (Pondimin^®) as well as a combination fenfluramine-phentermine (Fen/Phen^®) drug, were taken off the market when they were shown to cause potentially fatal heart defects. In November 1997, the U.S. Food and Drug Administration (FDA) approved a new weight-loss drug, sibutramine, (Meridia^®). Available only with a doctor’s prescription, Meridia^® can significantly elevate blood pressure and cause dry mouth, headache, constipation, and insomnia. This medication should not be used by patients with a history of congestive heart failure, heart disease, stroke, or uncontrolled high blood pressure.

The Chinese herb ephedra (Ephedra sinica ), combined with caffeine, exercise, and a low-fat diet in doctor-supervised weight-loss programs, is an alternative approach that can cause at least a temporary weight loss. However, the large doses of ephedra required to achieve the desired result can also cause serious medical problems including high blood pressure, heart attack, seizures, stroke, and death. Ephedra should not be used by anyone with a history of diabetes, heart disease, or thyroid problems. Diuretic herbs, which increase urine production, can cause short-term weight loss but cannot help patients achieve lasting weight control.

Acupressure and acupuncture can also suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that enhances the patient’s determination to lose weight. By improving physical strength, mental concentration, and emotional serenity, yoga can provide the same benefits.

Healthy lifestyles

The best approach to achieving and maintaining weight loss is a life-long commitment to regular exercise and sensible eating habits. Up to 85% of dieters who do not exercise on a regular basis will regain their lost weight within two years. In five years, the figure rises to 90%. Exercise increases the metabolic rate by

KEY TERMS

Adipose tissue —Fatty tissue.

Hydrostatic weighing —A technique to estimate percent body fat based on the density of an individual. Density is measured by immersing the person in a tank of water.

Metabolism —The sum total of all chemical reactions occurring in the body.

Obesity —A chronic, metabolic condition of excess body weight attributable to fat.

Skinfold caliper —A curved, hinged claw-shaped tool used to measure the thickness of skinfolds containing subcutaneous fat deposits. Skinfold thickness is correlated to percent body fat, thus skinfold calipers are used to estimate percent body fat.

creating muscle, which burns more calories than fat. When regular exercise is combined with regular, healthful meals, calories continue to burn at an accelerated rate for several hours. Obese people need to aim for permanent lifestyle changes of healthier eating, regular physical activity, and a better outlook toward food, because without a long-term commitment, body weight will slowly increase.

See also Genetics.

Resources

BOOKS

Cantor Goldberg, Merie. Weight-loss Surgery: Is It Right For You?. Garden City Park, NY: Square One Publishers, 2006.

Fairburn, Christopher G. and Kelly D. Brownell, eds. Eating Disorders and Obesity: A Comprehensive Handbook. New York: Guilford Press, 2005.

Kopelman, Peter G., Ian D. Caterson, and William H. Dietz, eds. Clinical Obesity in Adults and Children. Malden, MA: Blackwell Pub., 2005.

Lopez, Gail Woodward, ed. Obesity: Dietary and Developmental Influences. Boca Raton, FL: CRC/ Taylor & Francis, 2006.

Mela, David J. ed. Food, Diet, and Obesity. Boca Raton, FL: CRC Press, 2005.

PERIODICALS

Kiess, W., Galler, A., Reich, A., Muller, G., Deutscher, J., Raile, K., and J. Kratzsch. “Clinical Aspects of Obesity in Childhood and Adolescence.” Obesity Reviews (February 2001):29–36.

Terry Watkins

Obesity

Definition

Obesity is an abnormal accumulation of body fat, usually 20% or more over an individual's ideal body weight. Obesity is associated with increased risk of illness, disability, and death.

The branch of medicine that deals with the study and treatment of obesity is known as bariatrics. As obesity has become a major health problem in the United States, bariatrics has become a separate medical and surgical specialty.

Description

Obesity traditionally has been defined as body weight at least 20% above the weight corresponding to the lowest death rate for individuals of a specific height, sex, and age (designated as the ideal weight). Twenty to forty percent over ideal weight is considered mildly obese; 40–100% over ideal weight is considered moderately obese; and 100% over ideal weight is considered severely, or morbidly, obese. According to some estimates, approximately 25% of the United States population can be considered obese, 4 million of whom are morbidly obese. Other studies state that over 50% of American adults are obese, based on body mass index (BMI) measurements. Excessive weight can result in many serious, and potentially deadly, health problems, including hypertension , Type II diabetes mellitus (non-insulin dependent diabetes), increased risk for coronary disease, increased unexplained heart attack , hyperlipidemia, infertility , and a higher prevalence of colon, prostate, endometrial, and possibly, breast cancer . Approximately 300,000 deaths a year are attributed to obesity, prompting leaders in public health, such as former Surgeon General C. Everett Koop to label obesity "the second leading cause of preventable deaths in the United States."

Causes & symptoms

The mechanism for excessive weight gain is clear—more calories are consumed than the body burns, and the excess calories are stored as fat (adipose) tissue. However, the exact cause is not as clear and likely arises from a complex combination of factors. Genetic factors significantly influence how the body regulates appetite and the rate at which it turns food into energy (metabolic rate). Studies of adoptees confirm this relationship. The majority of adoptees followed a pattern of weight gain that more closely resembled that of their birth parents than their adoptive parents. A genetic predisposition to weight gain, however, does not automatically mean that a person will be obese. Eating habits and patterns of physical activity also play a significant role in the amount of weight a person gains.

Some recent studies have indicated that the amount of fat in a person's diet may have a greater impact on weight than the number of calories the food contains. Carbohydrates like cereals, breads, fruits and vegetables, and protein (fish, lean meat, turkey breast, skim milk) are converted to fuel almost as soon as they are consumed. Most fat calories are immediately stored in fat cells, which add to the body's weight and girth as they expand and multiply. There is continuing research on the theory that fat is metabolized as fuel and energy and that only excess carbohydrates are converted to stored fat. Current evidence shows that weight gain comes mostly from total calories consumed, rather than from the amount of carbohydrates. A study published in 2002 found that low-fat diets are no more effective in weight reduction programs than low-calorie diets. At any rate, a sedentary life-style, particularly prevalent in affluent societies like the United States, can contribute to weight gain. Psychological factors, such as depression and low self-esteem may, in some cases, also play a role in weight gain.

At what stage of life a person becomes obese can effect his or her ability to lose weight. In childhood, excess calories are converted into new fat cells (hyperplastic obesity), while excess calories consumed in adulthood only serve to expand existing fat cells (hypertrophic obesity). Since dieting and exercise can only reduce the size of fat cells, not eliminate them, persons who were obese as children can have great difficulty losing weight, since they may have up to five times as many fat cells as someone who became overweight as an adult.

Obesity can also be a side effect of certain disorders and conditions, including:

• Cushing's syndrome, a disorder involving the excessive release of the hormone cortisol

• hypothyroidism, a condition caused by an underactive thyroid gland
• neurologic disturbances, such as damage to the hypothalamus, a structure located deep within the brain that helps regulate appetite
• consumption of certain drugs, such as steroids, antipsychotic medications, or antidepressants

The major symptoms of obesity are excessive weight gain and the presence of large amounts of fatty tissue. Obesity can also give rise to several secondary conditions, including:

• arthritis and other orthopedic problems, such as lower back pain
• heartburn
• high cholesterol levels
• high blood pressure
• menstrual irregularities or cessation of menstruation (amenorhhea)
• shortness of breath that can be incapacitating
• skin disorders, arising from the bacterial breakdown of sweat and cellular material in thick folds of skin or from increased friction between folds

Diagnosis

Dignosis of obesity is made by observation and by comparing the patient's weight to ideal weight charts. Many doctors and obesity researchers refer to the body mass index (BMI), which uses a height-weight relationship to calculate an individual's ideal weight and personal risk of developing obesity-related health problems. Physicians may also obtain direct measurements of an individual's body fat content by using calipers to measure skin-fold thickness at the back of the upper arm and other sites. The most accurate means of measuring body fat content involves immersing a person in water and measuring relative displacement; however, this method is very impractical and is usually only used in scientific studies requiring very specific assessments. Women whose body fat exceeds 30% and men whose body fat exceeds 25% are generally considered obese.

Doctors may also note how a person carries excess weight on his or her body. Studies have shown that this factor may indicate whether or not an individual has a predisposition to develop certain diseases or conditions that may accompany obesity. "Apple-shaped" individuals who store most of their weight around the waist and abdomen are at greater risk for cancer, heart disease, stroke , and diabetes than "pear-shaped" people whose extra pounds settle primarily in their hips and thighs.

Treatment

Treatment of obesity depends primarily on the degree of a person's overweight and his or her overall health. However, to be successful, any treatment must affect life-long behavioral changes rather than short-term weight loss. "Yo-yo" dieting, in which weight is repeatedly lost and regained, has been shown to increase a person's likelihood of developing fatal health problems than if the weight had been lost gradually or not lost at all. Behavior-focused treatment should concentrate on:

• What a person eats and how much. This aspect may involve keeping a food diary and developing a better understanding of the nutritional value and fat content of foods. It may also involve changing grocery shopping habits (e.g. buying only what is on a prepared list and going only on a certain day), timing of meals (to prevent feelings of hunger, a person may plan frequent small meals), and actually slowing down the rate at which a person eats.
• How a person responds to food. This may involve understanding what psychological issues underlie a person's eating habits. For example, one person may binge eat when under stress , while another may always use food as a reward. In recognizing these psychological triggers, an individual can develop alternate coping mechanisms that do not focus on food.
• How people spend their time. Making activity and exercise an integral part of everyday life is a key to achieving and maintaining weight loss. Starting slowly and building endurance keeps individuals from becoming discouraged. Varying routines and trying new activities also keeps interest high.

For most who are mildly obese, these behavior modifications entail lifestyle changes they can make independently while being supervised by a family physician. Other mildly obese persons may seek the help of a commercial weight loss program (e.g. Weight Watchers). The effectiveness of these programs is difficult to assess, since programs vary widely, dropout rates are high, and few employ members of the medical community. However, programs that emphasize realistic goals, gradual progress, sensible eating, and exercise can be very helpful and are recommended by many doctors. Programs that promise instant weight loss or feature severely restricted diets are not effective and, in some cases, can be dangerous.

For individuals who are moderately obese, medically supervised behavior modification and weight loss are required. While doctors will put most moderately obese patients on a balanced low-calorie diet (1200–1500 calories a day), they may recommend that certain individuals follow a very low-calorie liquid protein diet (400–700 calories) for as long as three months. This therapy, however, should not be confused with commercial liquid-protein diets or commercial weight-loss shakes and drinks. Doctors tailor these diets to specific patients, monitor patients carefully, and use them for only a short period of time. In addition to reducing the amount and type of calories consumed by the patient, doctors will recommend professional therapists or psychiatrists who can help the individual effectively change his or her behavior in regard to eating.

The Chinese herb ephedra (Ephedra sinica, or ma huang), combined with exercise and a low-fat diet in physician-supervised weight-loss programs, can cause at least a temporary increase in weight loss. However, the large doses of ephedra required to achieve the desired result can also cause:

• anxiety
• heart arrhythmias
• heart attack
• high blood pressure
• insomnia
• irritability
• nervousness
• seizures
• strokes
• death

Ephedra should not be used by anyone with a history of diabetes, heart disease, or thyroid problems. It is not recommended for long-term use, and can cause serious medical or psychiatric problems if used too long. An article that appeared in the Journal of the American Medical Association in early 2003 advised against the use of ephedra.

Diuretic herbs, which increase urine production, can cause short-term weight loss but cannot help patients achieve lasting weight control. The body responds to heightened urine output by increasing thirst to replace lost fluids, and patients who use diuretics for an extended period of time eventually start retaining water again anyway. In moderate doses, psyllium , a mucilaginous herb available in bulk-forming laxatives like Metamucil, absorbs fluid and makes patients feel as if they have eaten enough. Red peppers and mustard help patients lose weight more quickly by accelerating the metabolic rate. They also make people more thirsty, so they crave water instead of food. Walnuts contain serotonin, the brain chemical that tells the body it has eaten enough. Dandelion (Taraxacum officinale ) can raise metabolism and counter a desire for sugary foods.

The amino acid 5-hydroxytryptophan, or 5-HTP , which is extracted from the seeds of the Griffonia simplicifolia plant, is thought to increase serotonin levels in the brain. Serotonin is a neurotransmitter, or brain chemical, that regulates mood and thus can be linked to mood-related eating behaviors. When physical and mental stress reduces serotonin levels in the body, 5-HTP may be helpful in regulating mood by boosting serotonin levels. Individuals should consult with their healthcare professional before taking 5-HTP, as the amino acid may interact with other medications and can have potentially serious side effects.

Acupressure and acupuncture can also suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that enhances the patient's determination to lose weight. By improving physical strength, mental concentration, and emotional serenity, yoga can provide the same benefits. Also, patients who play soft, slow music during meals often find that they eat less food but enjoy it more.

Eating the correct ratio of protein, carbohydrates, and good-quality fats can help in weight loss via enhancement of metabolism. Support groups and self-help groups such as Overeaters Anonymous and TOPS (Taking Off Pounds Sensibly) that are informed about healthy, nutritious, and balanced diets can offer an individual the support he or she needs to maintain this type of eating regimen.

Allopathic treatment

For individuals who are severely obese, dietary changes and behavior modification may be accompanied by surgery to reduce or bypass portions of the stomach or small intestine. The risks of obesity surgery have declined in recent years, but it is still only performed on patients for whom other strategies have failed and whose obesity seriously threatens their health. Other surgical procedures are not recommended, including liposuction, a purely cosmetic procedure in which a suction device is used to remove fat from beneath the skin, and jaw wiring, which can damage gums and teeth and cause painful muscle spasms.

A newer approach to weight loss is the development of functional foods, which are food products that incorporate natural compounds shown to help in weight loss programs. These compounds include carbohydrates with a low glycemic index, which help to suppress appetite; green tea extract, which increases the body's energy expenditure; and chromium , which encourages the body to burn stored fat rather than lean muscle tissue. Functional food products are currently undergoing clinical testing.

Appetite suppressant drugs are sometimes prescribed to aid in weight loss. These drugs work by increasing levels of serotonin or catecholamine, which are brain chemicals that control moods and feelings of fullness. Appetite suppressants, though, are not considered truly effective, since most of the weight lost while taking them is usually regained after stopping. Also, suppressants containing amphetamines can be potentially abused by patients. While most of the immediate side effects of these drugs are harmless, the long-term effects in many cases, are unknown. Two drugs, dexfenfluramine hydrochloride (Redux) and fenfluramine (Pondimin) as well as a combination fenfluramine-phentermine (Fen/Phen) drug, were taken off the market when they were shown to cause potentially fatal heart defects. In 1999, the United States Food and Drug Administration (FDA) approved a new prescription weight loss drug, Orlistat. Unlike other anti-obesity drugs that act as appetite suppressants, Orlistat encourages weight loss by inhibiting the body's ability to absorb dietary fat. The drug can cause side effects of abdominal cramping, gas , and diarrhea .

Other weight-loss medications available with a doctor's prescription include:

• Sibutramine (Meridia)
• Diethylpropion (Tenuate, Tenuate Dospan)
• Mazindol (Mazanor, Sanorex)
• Phendimetrazine (Bontril, Prelu-2)
• Phentermine (Adipex-P, Fastin, Ionamin, Oby-Cap)

Phenylpropanolamine (Acutrim, Dextarim) is the only nonprescription weight-loss drug approved by the FDA. These over-the-counter diet aids can boost weight loss by 5%. Combined with diet and exercise and used only with a doctor's approval, prescription anti-obesity medications enable some patients to lose 10% more weight than they otherwise would. Most patients regain lost weight after discontinuing use of either prescription medications or nonprescription weight-loss products.

Prescription medications or over-the-counter weight loss products can cause:

• constipation
• dry mouth
• headache
• irritability
• nausea
• nervousness
• sweating

None of the weight loss drugs should be used by patients taking monoamine oxidate inhibitors (MAO inhibitors).

Doctors sometimes prescribe fluoxetine (Prozac), an antidepressant that can increase weight loss by about 10%. Weight loss may be temporary and side effects of this medication include diarrhea, fatigue , insomnia, nausea, and thirst. Weight loss drugs currently being developed or tested include ones that can prevent fat absorption or digestion, reduce the desire for food and prompt the body to burn calories more quickly, and regulate the activity of substances that control eating habits and stimulate overeating.

Expected results

As many as 85% of dieters who do not exercise on a regular basis regain their lost weight within two years. In five years, the figure rises to 90%. Repeatedly losing and regaining weight (yo-yo dieting) encourages the body to store fat and may increase a patient's risk of developing heart disease. The primary factor in achieving and maintaining weight loss is a lifelong commitment to regular exercise and sensible eating habits.

Prevention

Obesity experts suggest that a key to preventing excess weight gain is monitoring fat consumption rather than counting calories, and the National Cholesterol Education Program maintains that only 30% of calories should be derived from fat. Only one-third of those calories should be contained in saturated fats (the kind of fat found in high concentrations in meat, poultry, and dairy products). Because most people eat more than they think they do, keeping a detailed food diary is a useful way to assess eating habits. Eating three balanced, moderate-portion meals a day—with the main meal at mid-day—is a more effective way to prevent obesity than fasting or crash diets. Exercise increases the metabolic rate by creating muscle, which burns more calories than fat. When regular exercise is combined with regular, healthful meals, calories continue to burn at an accelerated rate for several hours. Finally, encouraging healthful habits in children is a key to preventing childhood obesity and the health problems that follow in adulthood.

New directions in obesity treatment

The rapid rise in the incidence of obesity in the United States since 1990 has prompted researchers to look for new treatments. One approach involves the application of antidiabetes drugs to the treatment of obesity. Metformin (Glucophage), a drug that was approved by the Food and Dug Administration (FDA) in 1994 for the treatment of type 2 diabetes, shows promise in treating obesity associated with insulin resistance .

Another field of obesity research is the study of hormones, particularly leptin, which is produced by fat cells in the body, and ghrelin, which is secreted by cells in the lining of the stomach. Both hormones are known to affect appetite and the body's energy balance. Leptin is also related to reproductive function, while ghrelin stimulates the pituitary gland to release growth hormone. Further studies of these two hormones may lead to the development of new medications to control appetite and food intake.

A third approach to obesity treatment involves research into the social factors that encourage or reinforce weight gain in humans. Researchers are looking at such issues as the advertising and marketing of food products; media stereotypes of obesity; the development of eating disorders in adolescents and adults; and similar questions.

Resources

BOOKS

Ackerman, Norman. 5-HTP: The Natural Way to Overcome Depression, Obesity, and Insomnia. New York: Bantam Books, 1999.

Flancbaum, Louis, MD, with Erica Manfred and Deborah Biskin. The Doctor's Guide to Weight Loss Surgery. West Hurley, NY: Fredonia Communications, 2001.

Harris, Dan R., ed. Diet and Nutrition Sourcebook. Detroit, MI: Omnigraphics, 1996.

"Nutritional Disorders: Obesity." Section 1, Chapter 5 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.

PERIODICALS

Aronne, L. J., and K. R. Segal. "Weight Gain in the Treatment of Mood Disorders." Journal of Clinical Psychiatry 64 (2003 Supplement 8): 22–29.

Bell, S. J., and G. K. Goodrick. "A Functional Food Product for the Management of Weight." Critical Reviews in Food Science and Nutrition 42 (March 2002): 163–178.

Brudnak, M. A. "Weight-Loss Drugs and Supplements: Are There Safer Alternatives?" Medical Hypotheses 58 (January 2002): 28–33.

Colquitt, J., A. Clegg, M. Sidhu, and P. Royle. "Surgery for Morbid Obesity." Cochrane Database Systems Review 2003: CD003641.

Espelund, U., T. K. Hansen, H. Orskov, and J. Frystyk. "Assessment of Ghrelin." APMIS Supplementum 109 (2003): 140–145.

Hundal, R. S., and S. E. Inzucchi. "Metformin: New Understandings, New Uses." Drugs 63 (2003): 1879–1894.

Pirozzo, S., C. Summerbell, C. Cameron, and P. Glasziou. "Advice on Low-Fat Diets for Obesity (Cochrane Review)." Cochrane Database Systems Review 2002: CD003640.

Schurgin, S., and R. D. Siegel. "Pharmacotherapy of Obesity: An Update." Nutrition in Clinical Care 6 (January-April 2003): 27–37.

Shekelle, P. G., M. L. Hardy, S. C. Morton, et al. "Efficacy and Safety of Ephedra and Ephedrine for Weight Loss and Athletic Performance: A Meta-Analysis." Journal of the American Medical Association 289 (March 26, 2003): 1537–1545.

Tataranni, P. A. "Treatment of Obesity: Should We Target the Individual or Society?" Current Pharmaceutical Design 9 (2003): 1151–1163.

Veniant, M. M., and C. P. LeBel. "Leptin: From Animals to Humans." Current Pharmaceutical Design 9 (2003): 811–818.

ORGANIZATIONS

American Dietetic Association. (800) 877-1600. <www.eatright.org.>.

American Obesity Association (AOA). 1250 24th Street NW, Suite 300, Washington, DC 20037. (202) 776-7711 or (800) 98-OBESE. <www.obesity.org>.

American Society of Bariatric Physicians. 5453 East Evans Place, Denver, CO 80222-5234. (303) 770-2526. <www.asbp.org>.

American Society for Bariatric Surgery. 7328 West University Avenue, Suite F, Gainesville, FL 32607. (352) 331-4900. <www.asbs.org>.

North American Association for the Study of Obesity. 8630 Fenton St., Suite 412, Silver Spring, MD, 20910. (301) 563-6526. <www.naaso.org.>.

Overeaters Anonymous. P.O. Box 44020, Rio Rancho, New Mexico, 87174-4020. (505) 891-2664. <www.overeatersanonymous.org.>.

Weight-control Information Network (WIN). 1 WIN Way, Bethesda, MD 20892-3665. (202) 828-1025 or (877) 946-4627.

Paula Ford-Martin

Rebecca J. Frey, PhD

Obesity

Definition

Obesity is the condition of having an excessive accumulation of fat in the body, resulting in a body weight more than 20% above the average for height, age, sex, and body type, and in elevated risk of disability, illness, and death.

Description

The human body is composed of bone, muscle, specialized organ tissues, and fat. Together, all of these tissues comprise the total body mass, which is measured in pounds. Fat, or adipose tissue, is a combination of essential fat (an energy source for the normal physiologic function of cells and organs) and storage fat (a reserve supply of energy for future needs). When the amount of energy consumed as food exceeds the amount of energy expended in the normal maintenance of life processes and in physical activity, storage fat accumulates in excessive amounts. Essential fat is tucked in and around internal organs, and is an important building block of all cells in the body. Storage fat accumulates in the chest and abdomen, and, in much greater volume, under the skin.

Causes and symptoms

The human body was designed for life forty thousand years ago, when the ability to store energy in times of plenty meant the difference between life and death during famine. This protective mechanism is a source of trouble when food, in unlimited quantities, is readily available,. This is evident in the increasing prevalence of obesity in modern times, particularly in Western cultures. While obesity is just an exaggeration of a normal body, the storage of energy for future is properly classified as a health problem. This is because excessive amounts of storage fat may interfere with the normal physiology of the body. Obesity is directly related to the increasing prevalence of Type II diabetes in American society and for the appearance of Type II diabetes in children, previously a rarity. Because obesity promotes degenerative disease of joints and heart and blood vessels, it increases the need for some surgical procedures. At the same time, surgical complication rates are higher in obese patients. Obesity contributes to fatigue , high blood pressure, menstrual disorders, infertility, digestive complaints, low levels of physical fitness, and to the development of some cancers. The social costs of obesity that include decreased productivity, discrimination, depression, and low self-esteem, are less easily described and measured. Worldwide, obesity has reached epidemic proportions in the last thirty years, affecting both sexes and all ethnic, age, and socioeconomic groups. More than 50% of adults in the United States currently fall into overweight or obese classifications, and 22% of preschool children are classified as overweight. The increasing prevalence of obesity and diabetes in children and young adults heralds spiraling health care costs in the near future.

Because obesity reflects an imbalance between the amount of energy taken into the body in the form of food and the amount of energy expended in metabolism and physical activity, and because eating is an activity that involves choice and volition, obesity is classified by the Health Care Financing Administration (HCFA) as a "behavior" rather than as a disease. In recent years, following a pattern established in other behavioral problems such as alcoholism, researchers have attempted to establish a biologic basis for the development of obesity. They have succeeded in identifying many markers of the biochemical mechanisms that appear to be involved in feedback loops that control energy balance. However, much of the information is extrapolated from experimental work in rodents. Leptin, a hormone produced in fat cells is an example of such a marker. Leptin excited a great deal of hope as a potential treatment of obesity, but, as with many other laboratory discoveries, the hormone has proved far more complex and less easily understood in humans. Research to date indicates that obesity is the end product of numerous contributing factors, including genetics, hormonal influences, behavioral tendencies, medication effects, and the surrounding society. But the rapid and widespread increase in obesity in the last thirty years reflects changes in activity patterns and in eating habits, not a change in the human genetic pool or in physiology.

Diagnosis

There are two methods of diagnosing obesity. The first method is inspection—whereby an excessive amount of storage fat is usually noticeable upon visual inspection. The second method is inference of body fat content, obtained from body measurements such as weight or skinfold thickness, and comparison with charts of similar measurements in broad populations. The determination of obesity is based on the amount of variance from "normal," a value that comes from statistics on death rates in people with similar measurements. Calculations such as the body mass index (BMI) use a height-weight relationship to calculate an individual's ideal weight and personal risk of developing obesityrelated health problems. An individual with a BMI of25.9–29, for example, is considered overweight; a person with a BMI over 30 is classified as obese.

The problem with using weight as a measure of obesity is the fact that weight does not accurately represent body composition. A heavily-muscled football player may weigh far more than a sedentary man of similar height, but have significantly less body fat. Chronic dieters, who have lost significant muscle mass during periods of caloric deprivation, may look slim and weigh little, but have elevated body fat percentages. The most accurate means of estimating body fat content involves weighing a person two ways: First, the person is weighed under water. The difference between dry and underwater weight is calculated to obtain the volume of water displaced by the mass of the body. While this method is impractical, it has the advantage of determining body composition most accurately, and is the truest reflection of the actual percentage of body mass that is fat. Women whose body fat exceeds 30% of total body mass and men whose body fat exceeds 25% are generally considered obese.

The pattern of fat distribution on the body may indicate whether an individual has a predisposition to develop certain diseases or conditions that may accompany obesity. "Apple-shaped" individuals who store most of their weight around the waist and abdomen are at greater risk for cancer, heart disease, stroke , and diabetes than "pear-shaped" people, whose extra pounds settle primarily on their hips and thighs.

Treatment

Since obesity develops when intake of the food required to produce energy exceeds the amount of energy used in metabolism and in physical activity, the treatment of obesity must alter one or both aspects of the energy stream. The options are to decrease energy intake or to increase energy output, or both. However, the problem does not yield rapidly to either method. Storage fat is meant to protect its bearer from starvation when food is unavailable, and before fat is tapped for energy. In the face of decreased intake of food, the body breaks down muscle to construct the sugar it needs to feed the brain . Much of the early weight loss on a very low calorie diet represents loss of muscle tissue rather than loss of fat. Similarly, fat is not easy to access as fuel for exercise. A person of normal weight (according to one of the charts as described above) has enough body fat to fuel the muscles for days of continuous running, but will collapse long before burning any significant amount fat stored by the body.

When obesity develops in childhood, the total number of fat cells increases (hyperplastic obesity), whereas in adulthood, it is the total amount of fat in each cell that increases (hypertrophic obesity). Decreasing the amount of energy (food) consumed or increasing the amount of energy expended cannot change the number of fat cells already present. These actions can only reduce the amount of fat in each cell, and only if the process is slow and steady—as it was in reverse, when the excess fat accumulated. Prevention, as in so many problems, is far superior to any available treatment of obesity.

The strategy for weight loss in obese patients is first to change behavior; then, it is to decrease the expectation of rapid change. Behavioral treatment is goal-directed, process-oriented, and relies heavily on self-monitoring. Emphasis is on:

• Food intake: The potential energy provided by food is measured in calories, and the capacity of a certain type and amount of food to provide energy is called its caloric content. Keeping a food diary and developing a better understanding of the nutritional value and fat content of foods, changing grocery-shopping habits, paying attention to timing and appearance of meals, and slowing the speed of eating all help to modify food intake.
• Response to food: The body is capable of matching energy intake and output perfectly, but, in obese individuals, food intake is often unrelated from physiologic cues. Eating occurs for many reasons other than hunger. What psychological issues underlie the eating habits? Does stress cause binge eating ? Is food seen as a reward? Recognition of psychological triggers is necessary for the development of alternate coping mechanisms that do not focus on food.
• Time usage: The body is suited for an ancient world in which physical activity was a necessity. In the modern world, physical activity must be a conscious choice. Making activity and exercise an integrated part of everyday life is a key to achieving and maintaining weight loss. Sedentary and overweight individuals have to reclaim slowly the endurance that is natural by managing their time to allow for gradual increases in both programmed and conscious lifestyle activity.

Behavior modification

For most individuals who are mildly obese, behavior modifications entail life-style changes they can make independently if they have access to accurate information and have reached the point of readiness to make a serious commitment to losing weight. A family physician's evaluation is helpful, particularly in regard to exercise capacity and nutritional requirements. Commercial weight-loss programs may be helpful for some mildly obese individuals, but they are of varying quality. A good program emphasizes realistic goals, gradual progress, sensible and balanced eating, and increased physical activity; it is often recommended by physicians. Programs that promise instant weight loss or feature severe restrictions in types and amounts of food are not effective, and, in some cases, can be dangerous.

For individuals who are moderately obese, medically supervised behavior modification and weight loss are more likely to be effective than an independent program. A realistic goal is loss of 10% of current weight over a six-month period. While doctors put most moderately obese patients on balanced, low-calorie diets (1,200–1,500 calories a day), occasionally they recommend a very low calorie liquid protein diet (400–700 calories), with supplementation of vitamins and minerals, for as long as three months. Professional help with behavior modification is of paramount importance in such cases; without changing eating habits and exercise patterns, weight lost will be regained quickly.

Surgery

For individuals who are morbidly obese, surgery to bypass portions of the stomach and small intestine may at times be the only effective means of producing sustained and significant weight loss. Such obesity surgery, however, can be risky, and it is performed only on patients for whom other strategies have failed and whose obesity seriously threatens health. Liposuction is a purely cosmetic procedure in which a suction device is used to remove fat from beneath the skin, and has no place in the treatment of obesity.

Medications

Most of the current research on obesity is aimed at identifying biochemical pathways that will be amenable to intervention with drug treatments. These medications would be specifically tailored to interfere with the energy cycles to facilitate weight loss. As of 2002, there are two major classes of drugs that are approved for the treatment of obesity by the U.S. Food and Drug Administration (FDA). History of the field is littered with drugs that have failed or that have caused serious side effects. Appetite suppressant drugs such as Dexatrim and Meridia (sibutramine) change the amounts of some neurotransmitters in the brain. These chemical changes result in decreased appetite, but only in the presence of the drug. Digestive inhibitors such as Orlistat (Xenical) are drugs that interfere with the breakdown and absorption of dietary fat in the intestines; they are, however, poorly tolerated by the person who is obese because the effects of fat malabsorption are unpleasant.

These drugs also interfere with the absorption of some necessary vitamins. Fat substitutes such as Olestra, while technically not drugs, attempt to recreate the pleasant taste that fat adds to food, but create the same negative side effects as digestive inhibitors. Unless an obese individual has also made necessary behavioral changes, excess weight returns quickly when appetite suppressants or malabsorptive agents are stopped.

The use of any drug is associated with unwanted side effects, so that the decision to take a drug must come after the potential side effects are weighed against the potential benefits. No drug, current or past, has had such dramatic effects on obesity that it warrants its casual use. While most of the immediate side effects that may occur are reversible, the long-term effects, in many cases, are unknown. Even after a new drug successfully negotiates the stringent FDA approval process, its widespread use over a longer time frame may lead to the side effects that were not initially observable in the test population. Two popular obesity drugs of the early 1990s have already been withdrawn from the market because of unanticipated and severe cardiac problems. Meridia, just released in 1997, is already under scrutiny by a consumer group for its relationship to several deaths. Nevertheless, studies show that when obesity drugs are combined with behavioral changes—and especially with a portion controlled diet—weight loss is significantly greater than in a control group treated with behavior modification alone, at least after six months. It remains to be proved whether drug-assisted weight loss is long lasting.

Alternative treatment

The Chinese herb, ephedra (Ephedra sinica ), combined with caffeine, exercise, and a low-fat diet, can cause a temporary increase in weight loss, at best. However, ephedra and caffeine are both central nervous system (CNS) stimulants, and the large doses of ephedra required to achieve the weight loss can also cause anxiety, irritability, and insomnia . Further, ephedra has been implicated in more serious conditions, such as seizure and stroke. Ephedra should not be used by anyone with a history of diabetes, heart disease, or thyroid problems.

Diuretic herbs, which increase urine production, can cause short-term weight loss, but cannot help patients achieve lasting weight control. The body responds to heightened urine output by increasing thirst to replace lost fluids, and patients who use diuretics for an extended period of time retain water even in the presence of the diuretic. In moderate doses, psyllium, a mucilaginous herb available in bulk-forming laxatives like Metamucil, absorbs fluid and makes patients feel as if they have eaten enough. Red peppers, mustard, and dandelion are said to generate weight loss by accelerating the metabolic rate. Dandelion also counteracts the desire for sweet foods. Walnuts contain serotonin, the brain chemical that signals satiety.

Acupressure and acupuncture can also suppress food cravings. Visualization and meditation can create and reinforce a positive self-image that enhances determination to lose weight. By improving physical strength, mental concentration and emotional serenity, yoga can provide the same benefits.

The correct balance of the basic food groups is also important, and believed by some experts to enhance the metabolic rate.

Prognosis

As many as 85% of dieters who do not exercise on a regular basis regain their lost weight within two years. In five years, the figure rises to 90%. Repeatedly losing and regaining weight (yo-yo dieting) encourages the body to store fat and may increase a patient's risk of developing heart disease. The primary factor in achieving and maintaining weight loss is a lifelong commitment to regular exercise and sensible eating habits.

Prevention

Obesity experts suggest that a key to preventing excess weight gain is monitoring fat consumption rather than counting calories; in fact, the National Cholesterol Education Program maintains that only 30% of calories should be derived from fat. Only one-third of those calories should come from saturated fats (the kind of fat found in high concentrations in meat, poultry, and dairy products). However, total caloric intake cannot be ignored, since it usually the slow accumulation of excess caloric intake, regardless of its source, that results in obesity. Erring on the side of 25 excess calories a day, a single cookie will result in a five-pound weight gain by the end of a year. Without recognition of the problem, weight balloons up another 45 pounds by the end of 10 years, and the return to normal weight is an arduous process. Because most people eat more than they think they do, keeping a detailed and honest food diary is a useful way to recognize eating habits. Eating three balanced, moderate-portion meals a day—with the main meal at mid-day—is a more effective way to prevent obesity than fasting or crash diets, which convince the body that there is an ongoing famine. After 12 hours without food, the body has depleted its stores of readily available energy, and hunkers down to begin protecting itself for the long term. Metabolic rate starts to slow, and breakdown of muscle tissue for the raw materials needed for energy maintenance begins. Until more food appears, famine mode persists and deepens; when the fast is lifted, the body is in a state of slowed metabolism, has a bit less muscle, and requires less food than before the fast. Exercise increases the metabolic rate by creating muscle, which burns more calories than fat. When regular exercise is combined with consistent, healthful meals, calories continue to burn at an accelerated rate for several hours.

Finally, encouraging healthful habits in children is a key to preventing childhood obesity and the health problems that follow in adulthood.

Resources

BOOKS

Aronne, Louis J. "Obesity and Weight Management." In Textbook of Primary Care Medicine. 3rd ed. Edited by John Noble, M.D. St. Louis, MO: Mosby, 2001.

The Editors of Time-Life Books. The Medical Advisor: The Complete Guide to Alternative & Conventional Treatments. Alexandria, VA: Time Life, Inc. 1996.

Harris, Dan R., ed. Diet and Nutrition Sourcebook. Detroit, MI: Omnigraphics, 1996.

Wilmore, Jack H. and David L. Costill. "Obesity, Diabetes, and Physical Activity." In Physiology of Sport and Health. 2nd ed. Champaign, IL: Human Kinetics, 1999.

PERIODICALS

Jensen, Michael D., ed. "Obesity." Medical Clinics of North America 84, no.2 (March 2000): 305–518.

Lustig, Robert H. "The Neuroendocrinology of Obesity." Endocrinology and Metabolism Clinics 30, no. 3 (September 2001): 765–785.

Patel, Manesh R. and Darren K. McGuire. "Pounds of Prevention." American Heart Journal 142, no.3 (September 2001): 388–90.

Rocchini, Albert P. "Childhood Obesity and A Diabetes Epidemic." New England Journal of Medicine 346, no. 11 (March 14, 2002): 854–855.

ORGANIZATIONS

American Dietetic Association. 216 West Jackson Blvd., Chicago, IL 60606-6995. <http://www.eatright.org>.

American Obesity Association. 1250 24th St. NW, Washington D.C. 20037. <http://www.obesity.org>.

Shape Up America. 6707 Democracy Blvd., Suite 306, Bethesda, MD 20817. <http://www.shapeup.org/general/index.html>.

Weight-Control Information Network. 1 Win Way, Bethesda, MD 20892-3665. <http://www.niddk.nih.gov/health/nutrit/win.html>.

Elizabeth Reid, M.D.

OBESITY

OBESITY. Obesity and overweight now affect more than 50 percent of adult Americans. Diabetes mellitus, hypertension, heart disease, gallbladder disease, and some forms of cancer result from obesity. Whether these diseases are yet present or not, the obese individual should be encouraged to lose weight by appropriate methods to reduce the future likelihood that they will develop. Methods of weight loss include diet, nutritional education, self-help groups, and behavioral change. Under some circumstances drugs or surgery may be considered.

Definition and Measurement of Obesity

Obesity and overweight are best defined using the body mass index (BMI). This index is determined by dividing body weight in kilograms by the square of the height in meters: BMI = W/H². The normal rate for BMI is 18.5 to 25. A BMI between 25 and 30 kg/m² is defined as over-weight and a BMI above 30 kg/m² is defined as obesity (Table 1). Visceral fat can be used as an index of central adiposity. An increase in visceral fat reflects central obesity and increases health risks. The waist circumference is used to assess the amount of visceral obesity. A waist circumference in men of 40 inches (102 cm) or more, and in women, of 35 inches (88 cm) or more, is the threshold for defining central obesity (Table 1).

Prevalence of Overweight

More females than males are overweight at any age. The frequency of overweight increases with age to reach a peak at forty-five to fifty-four years in men and at age fifty-five to sixty-four in women. The National Health and Nutrition Examination Survey (NHANES) conducted by the U.S. government (published in 1993) found a BMI of 25 or more in 59.4 percent of men age twenty years or older and in 50.7 percent of women over the age of twenty years. The prevalence of obesity (BMI 30 or more) was 19.5 percent in men and 25.0 percent in women. The incidence of obesity continues to increase dramatically in the United States and elsewhere. A number of factors including age, sex, and physical inactivity influence the amount of body fat.

At birth, the human infant contains about 12 percent body fat. During the first years of life, body fat rises rapidly to reach a peak of about 25 percent by six months of age and then declines to 18 percent over the next ten years. At puberty, there is a significant increase in the percentage of body fat in females and a decrease in males. By age eighteen, males have approximately 15 to 18 percent body fat, and females have 25 to 28 percent. Between

ages twenty and fifty, the fat content of males approximately doubles and that of females increases by about 50 percent. Total body weight, however, rises by only 10 to 15 percent: fat now accounts for a larger part of the body weight and lean body mass decreases.

Risks Related to Obesity

As the BMI increases, there is a curvilinear rise in excess mortality. This excess mortality rises more rapidly when the BMI is above 30 kg/m². A BMI over 40 kg/m² is associated with a further increase in overall risk and for the risk of sudden death. The principal causes of the excess mortality associated with overweight include hypertension, stroke, and other cardiovascular diseases, diabetes mellitus, certain cancers, reproductive disorders, gall-bladder disease, and sudden death.

The insulin-resistant state or metabolic syndrome is strongly associated with visceral fat. It may include consequences such as glucose intolerance or type 2 diabetes mellitus, hypertension, polycystic ovarian syndrome, dyslipidemia (the state of abnormal—either higher or lower—values for blood fats), and other disorders. These are often responsive to weight loss, especially when this is achieved early and the loss is maintained.

Development of Obesity

Several mechanisms lead to obesity, including neuroendocrine imbalances, particular drugs, diet, reduced energy expenditure, and genetic factors that lead to certain syndromes and predisposition to obesity. Obesity can follow damage to the hypothalamus in the brain, but this is rare. Cushing's disease is somewhat more common and can result in obesity. Treatment should be directed at the cause of the increased formation of adrenal corticosteroids.

Treatment of diabetics with insulin, sulfonylureas, or thiazolidinediones (but not metformin) can increase hunger and food intake, resulting in weight gain. Treatment with some antidepressants, anti-epileptics, and neuroleptics can also increase body weight, as can cyproheptadine (a serotonin antagonist that produces weight gain), probably through effects on the monoamines (including norepinephrine, epinephrine, dopamine, histamine, and serotonin) in the central nervous system.

Eating a high-fat diet and excessive consumption of sugar-sweetened beverages and the prevalence of abundant varieties of food in cafeterias or supermarkets are dietary factors in the development of obesity. Reduced energy expenditure relative to energy intake is another major component. Energy expenditure can be divided into four parts.

An inactive individual at rest burns between 800 and 900 kilocalories during a twenty-four hour period. This rate is lower in females than in males, and declines with age, and could account for much of the increase in fat stores if food intake does not decline similarly. The effect of physical exercise on metabolism is variable but on average is responsible for about one-third of the daily energy expenditure. From a therapeutic point of view this component of energy expenditure is most easily manipulated. Dietary thermogenesis is the energy expenditure that follows the ingestion of a meal. Heat produced by eating may dissipate up to 10 percent of the ingested calories. These thermic effects of food are one type of metabolic "inefficiency" in the body, that is, where dietary calories are not available for "useful" work. In the obese, the thermic effects of food are reduced particularly in individuals with impaired glucose tolerance or diabetes. Acute over-or underfeeding will produce corresponding shifts in overall metabolism, which can be as large as 15 to 20 percent.

Genetic factors can produce some types of obesity that are easily recognized. Among these types of obesity are: (1) the Bardet-Biel syndrome, characterized by retinal degeneration, mental retardation, obesity, polydactyly, and hypogonadism; (2) the Alstrom syndrome, characterized by pigmentary retinopathy, nerve deafness, obesity, and diabetes mellitus; (3) Carpenter syndrome, characterized by acrocephaly (abnormalities in the facial and head bones), mental retardation, hypogonadism, obesity, and preaxial syndactyly (extra fingers or toes on one hand or foot); (4) the Cohen syndrome, characterized by mental retardation, obesity, hypotonia (reduced tone of the muscles, resulting in a "floppy" muscle mass), and characteristic facies (an appearance of the face that is typical of specific genetic diseases); (5) the Prader-Willi syndrome, characterized by hypotonia, mental retardation, hypogonadism, and obesity; and (6) the pro-opiomelanocortin (POMC) syndrome, characterized by defective production of POMC that is recognized as a red-headed fat child with a low plasma cortisol (a value that is below the normal range).

If both parents are obese, about 80 percent of their offspring will be obese. If only one parent is obese, the likelihood of obesity in the offspring falls to less than 10 percent. Studies with identical twins suggest that inheritance accounts for about 70 percent and environmental factors (diet, physical inactivity, or both) account for 30 percent of the variation in body weight. Deficiency of the gene leptin and deficiency of the leptin receptor are rare, but are associated with massive human obesity. Absence of convertase I has also been associated with obesity in one family. The most common defects associated with massive obesity are abnormalities in the melanocortin receptor system—up to 4 percent of massively obese people may have this type of defect.

Evaluation of the Obese Patient

A medical evaluation should include the expected medical history, family history, personal and social history, and review of the systems of the body with a particular focus on the medications that can cause weight gain. A physical examination should include an assessment of the patient's height, weight, waist circumference, blood pressure, and level of health risk due to obesity. Laboratory tests should include a lipid panel, glucose level, chemistry panel for hepatic (liver) function and uric acid, thyroid function testing, and, if indicated a cortisol level.

Evaluating Risk Using the Body Mass Index (BMI)

Individuals with a normal BMI (20–25 kg/m²) have little or no risk from obesity. Any individual in this weight range who wishes to lose weight for cosmetic reasons should do so only with conservative methods. Individuals with a BMI of greater than 25 to 29.9 kg/m² are in the low-risk group for developing heart disease, hypertension, gallbladder disease, and diabetes mellitus associated with obesity. They too should be encouraged to use low-risk treatments, such as caloric restriction and exercise. Individuals with a BMI of 27 to 30 kg/m² or more who have diseases related to obesity may use adjunctive pharmacotherapy for weight loss.

Individuals with a BMI of 30 to 40 kg/m², have moderate risk for developing diseases associated with obesity. Diet, drugs, and exercise would all appear to be appropriate forms of treatment. Individuals with significant degrees of excess weight often find exercise difficult. However, exercise is very important in helping to maintain weight loss. The use of weight loss medications, as an adjunct to treatment, may also be useful in this group. Individuals who have a BMI above 40 kg/m² have a high risk of developing diseases associated with their obesity. Moderate to severe restriction of calories is the first line of treatment, but for some of these patients surgery may be advisable.

Treatment of Obesity

Any diet must reduce an individual's caloric intake below daily caloric expenditure if it is to be successful. This requires an assessment of caloric requirements, by estimating caloric expenditure from desirable weight tables; for men, multiply desirable weight by 30 to 35 kilocalories/kilogram, (14–16 kilocalories/lb.); for women, multiply desirable weight by 25 to 30 kilocalories/kilogram (12–14 kilocalories/lb.). After assessing caloric requirements, a reasonable calorie deficit can be prescribed. A caloric deficit of 500 kilocalories/day (3,500 kilocalories/week) will produce the loss of approximately one lb. (0.45 kilograms) of fat tissue each week. Table 2 gives a list of diets divided into different levels of energy.

The very low calorie diet (below 800 kilocalories) was developed to facilitate the rate of weight loss since lower energy intake should lead to greater energy deficit. In free living people, however, diets with 400 kilocalories/day have not produced greater weight loss than those with 800 kilocalories/day, suggesting either that they are harder to adhere to or that there is an adaptation in energy expenditure. In either case, these diets should only be used under appropriate medical supervision.

Types of diets. There are several types of diets with more than 800 kilocalories/day that usually have more than 1,200 kilocalories/day. They can be divided into several categories. These categories are based on the relative proportion of macronutrients included in the diet and whether they use special foods. For all diets it must be true that they reduce the calorie intake to produce a negative energy balance. Low-carbohydrate diets are touted because they produce ketosis (a state of increased ketones associated with diabetes and fasting) and allow you to eat all of the protein and fat you want. This ends up reducing total calorie intake to about 1,500 kilocalories/day. Since these diets generally have carbohydrate levels below 50 g./day they are ketogenic and can be monitored clinically by the appearance of ketones in the urine. They vary in the level of fiber that is employed. The Atkins diet has low fiber levels, the Sugar Busters diet higher fiber levels.

Low-fat diets recommend fat intake in the range of 10 to 20 percent of calories. The higher carbohydrate increases fiber intake. These diets were developed in a setting designed to reverse the atherosclerotic plaques associated with risks for heart disease, but because of the high fiber content they were often associated with weight loss. Moderate fat levels with higher carbohydrates are characteristic of many widely recommended "healthy diets." For weight loss, the New York Health Department recommends the Prudent Diet, which has stood the test of time.

The portion-controlled diet makes use of prepared foods that have a narrow range of calories. This includes liquid or powdered drinks as well as frozen or canned entrees that have about 300 kilocalories/meal. These can be combined conveniently and thus removes the problem of counting calories from the individual. A number of popular diets focus on a single food, and although nutritionally unbalanced, they are simple to follow and the monotony of single items tends to limit food intake.

Food Guide Pyramid. The Food Guide Pyramid provides an approach to evaluating the quality of your diet. At the bottom of the pyramid are the grains, beans, and starchy vegetables that provide vitamins, minerals, fiber, and energy; six or more servings are recommended. On the next level are the vegetables (3–5 servings) and the fruits (3–4 servings). On the third level are the meats, fish, poultry, and nuts (2–3 servings) along with the milk and yogurt (2–3 servings). At the top are the fats, sweets, and alcohol. Reducing the number of servings proportionally will provide you with a calorie-reduced diet. Most important for the dieter, however, is to sharply reduce the fats and sugar at the top of the pyramid and to reduce or eliminate alcoholic beverages. Not only do alcoholic beverages have calories, their consumption tends to reduce the individual's control in selecting the quality and quantity of foods to eat.

Changing behavioral patterns of eating. The basic principles of behavioral approaches for obesity can be summarized under the ABCs of eating.

• The A stands for antecedent. If one looks at eating as the response to events in the environment, then the antecedent events are those that trigger eating.
• The B stands for the behavior of eating. This includes among other things the place, the rate, and the frequency with which an individual eats. If the act of eating can be focused at one place with one plate and place setting it can help to provide control over eating.
• The C is the consequence of the eating. The feelings an individual has about eating can be altered, and rewards for changing eating patterns can be instituted.

Exercise and physical activity. The only part of energy expenditure that is amenable to significant manipulation is physical activity. During sleep, the lowest level of activity, approximately 0.8 kilocalories/minute is consumed. Thus, if an individual sleeps for an entire 24 hours, approximately 1,150 calories will be expended. Reclining increases this level to approximately 1.0-1.4 kilocalories/minute. Obese and diabetic patients should be encouraged to increase their physical activity for two reasons: First, it consumes calories, but second, and more important, exercise increases glucose utilization and may improve insulin sensitivity.

Drug treatment of obesity. Only a few drugs have been approved by the Food and Drug Administration for treatment of obesity. Studies following individuals who have used these drugs for two years have been published for sibutramine (Meridia) and orlistat (Xenical). Weight-loss drugs should be reserved for patients with moderate-or high-risk obesity (BMI >30 kg/m²) or a BMI above 27 if they have other significant diseases related to obesity. They should be considered for the patient who has failed to lose weight with other methods. Herbal products containing ephedra and an herbal source of caffeine can also produce weight loss when used in accordance with the package instructions.

Surgery. Gastric operations reduce the size of or bypass the stomach, but should be reserved for people with a BMI above 40 or when recommended by a physician.

The Obese Child

Estimates of the prevalence of obesity in children range from 3 to 15 percent. This figure has been rising more rapidly than in the rest of the population. The appearance of obesity in childhood and particularly adolescence is important because it most often persists into adult life. It may be a precursor to the appearance of type 2 diabetes in adolescents. The possibility of treatment should be considered for children who are above the seventy-fifth percentile of weight for height, and might be encouraged for those who are above the ninety-fifth percentile of weight for height. The treatment of prepubertal children should probably involve both parents and child since at this age the principal control of food availability is in the hands of the parents. For adolescents, however, it may be better to separate patient and parents, since the interaction between these groups may be part of the problem. Where growth has not reached its fullest extent, dietary restriction should attempt to reduce further weight gain. Severe caloric restriction and the use of appetite-suppressing drugs may slow height growth. For both children and adolescents, involvement in a regular exercise program is probably the first line of treatment.

See also Anorexia, Bulimia; Body; Body Composition; Caloric Intake; Eating: Anatomy and Physiology of Eating; Fasting and Abstinence; Fats; Fiber, Dietary; Hunger, Physiology of.

BIBLIOGRAPHY

Bessesen, D. H., and R. Kushner. Evaluation and Management of Obesity. Center for Obesity Research and Education. Philadelphia: Hanley and Belfus, 2002.

Bray, George A. Contemporary Diagnosis and Management of Obesity. Newtown, Pa.: Handbooks in Health Care, 1998.

National Heart, Lung, and Blood Institute (NHLBI). Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults. Bethesda, Md., 1998.

Yanovski, J., and S. Z. Yanovski. "Obesity." New England Journal of Medicine 346, no. 8 (21 February 2002): 591–602.

George Bray