Dietary Treatment for Overweight and Obesity

We rarely repent of having eaten too little.

—Thomas Jefferson

Americans have long been consumed with losing weight, seemingly willing to suffer deprivation and to embrace each new diet that debuts—even if the ''new diet'' is simply a twist on a previous weight-loss plan. The fixation with weight loss is so long-standing that even the word diet has assumed a new meaning. As a verb, diet means to eat and drink a prescribed selection of foods; however, since the latter part of the twentieth century dieting became synonymous with an effort to lose weight.

During the nineteenth century, fashionable body shapes and sizes varied from decade to decade, but most periods celebrated plumpness as a sign of health and prosperity and considered being thin a sign of poverty and ill health. At the turn of the twentieth century, rising interest in dieting seemingly coincided with some of the social and cultural changes that would make it necessary: food became increasingly plentiful, and sedentary work and public transportation reduced Americans' level of physical activity. In Fat History: Bodies and Beauty in the Modern West (2002), Peter N. Stearns explains how fat became ''a turn-of-the-century target'' with anti-fat sentiments intensifying from the 1920s to the present.

Stearns asserts that the contemporary obsession with fat arose in tandem with the dramatic growth in consumer culture, women's increasing equality, and changes in women's sexual and maternal roles. Dieting, with its emphasis on deprivation, self-control, and moral discipline, seemed the perfect antidote to the indulgence of consumer culture, and Stearns contends that ''weight morality bore disproportionately on women precisely because of their growing independence, or seeming independence, from other standards.''

Fashion trends fueled anti-fat sentiments as women shed the corsets that had created the illusion of narrow waists and aspired to duplicate the wasp-waisted silhou-ettes by becoming slimmer. The shorter, close-fitting ''flapper'' dresses of the 1920s revealed women's legs and rekindled their desires to be slender. The emergence of the first actuarial tables (data compiled to assess insurance risk and formulate life insurance premiums), which showed the relationship between overweight and premature mortality (death), reinforced the growing sentiment that thinness was the key to health and longevity. Capitalizing on the increasing interest in monitoring and reducing body weight, the new Detecto and Health-o-Meter bathroom scales enabled people to weigh themselves regularly in the privacy of their own homes, as opposed to relying on periodic visits to the physician's office or pharmacy to use the balance scale.

SELECTED MILESTONES IN THE HISTORY OF DIETING

Not unlike fashion trends, the history of dieting reveals the emergence and popularity of specific diets, which over time are cast aside in favor of different approaches but then are recycled and resurface as ''new and miraculous.'' The first low-carbohydrate diet to earn popular acclaim was described by William Banting (1797-1878) in the 1860s. In Letter on Corpulence, Addressed to the Public (1863), Banting, then sixty-six years old, claimed that by adhering to his low-carbohydrate regimen he was never hungry and had lost 46 of his initial 202 pounds in one year.

The early 1900s marked the beginning of diets that restricted calories. Diet and Health, with Key to the Calories (1918) by Lulu Hunt Peters (1873-1930) advised readers to think in terms of consuming calories rather than food items and remained in print for twenty years. Peters wrote, ''You should know and use the word calorie as frequently, or more frequently, than you use the foot, yard, quart, gallon and so forth... hereafter you are going to eat calories of food. Instead of saying one slice of bread, or a piece of pie, you will say 100 calories of bread, 350 calories of pie.'' The 1920s also saw the rise of very-low-calorie diets to promote weight loss. For example, the Hollywood eighteen-day diet advised just 585 calories per day, which required the dieter to eat mostly citrus fruit.

Throughout the 1920s and 1930s the low-calorie diet remained a popular weight-loss strategy; however, other approaches, such as food-limiting plans that restricted dieters to just one or two foods (e.g., lamb chops, pineapples, grapefruits, or cabbage), were introduced, as were diets that prescribed combinations of certain foods and forbid others. For example, some diets prohibited eating protein and carbohydrates together; others were more specific, advising which vegetables could be served together. The 1930s also saw the first condemnations of carbohydrates as causes of overweight. A high-fat, lowfiber diet consisting primarily of milk and meat was thought to be protective against disease. The Italian poet Filippo Tommaso Marinetti (1876-1944) exhorted Italians to forgo their pasta because he claimed it made them sluggish, pessimistic, and fat.

In 1943 the U.S. Department of Agriculture (USDA) released the ''Basic Seven'' food guide in the National Wartime Nutrition Guide. It emphasized a patriotic wartime austerity diet that included between two to four servings of protein-rich meat and milk products, three servings of fruits or vegetables, and the rather vague recommendations of ''bread, flour, and cereals every day and butter, fortified margarine—some daily.''

In 1948 Esther Manz (1908-1996), a 5-foot, 2-inch, 208-pound homemaker established Take Off Pounds Sensibly (TOPS; http://www.tops.org/), the first support-group program for weight loss. Manz was inspired to start the program after she attended childbirth preparation classes, where women benefited from mutual support and encouragement. As of 2007, the annual membership of $24 supported the international nonprofit organization, which was based in Milwaukee. Along with weekly meetings and private weigh-ins, TOPS participants are encouraged to adhere toacalorie countingmealplanbased onaprogram developed by the American Dietetics Association. In 2007 TOPS boasted about two hundred thousand members in ten thousand chapters worldwide. Members who achieve their weight goals become KOPS (Keep Off Pounds Sensibly), and often keep attending meetings to maintain their weight and serve as role models for others.

In 1950 the American physician and biophysicist John Gofman (1918-2007) of the University of California at Berkeley hypothesized that blood cholesterol was involved in the rise in coronary heart disease. Gofman found not only that heart attacks correlated with elevated levels of cholesterol but also that the cholesterol was contained in one lipoprotein particle: low-density lipoprotein (LDL). Early reports of the connection between overweight and elevated blood cholesterol intensified interest in weight loss, which was now promoted as a strategy for preventing heart disease. During the late 1950s, injections of human chorionic gonadotropin, which was derived from the urine of pregnant women or animals, enjoyed fleeting popularity as a weight-loss agent; however, it was quickly proven entirely ineffective. Fad diets, such as a diet advocating the consumption of several bananas to satisfy sugar cravings, and another that involved ingesting a blend of oils to boost metabolism, continued to lure Americans seeking quick weight loss. In 1959 the American Medical Association called dieting a ''national neurosis.''

In 1960 Metrecal, the first high-protein beverage, was widely advertised by the Mead Johnson Company as a weight-reducing aid. It was originally sold as a powder, which when mixed with a quart of water yielded four eight-ounce glasses intended to serve as four meals per day, totaling nine hundred calories. The powder was made from milk, soy flour, starch, corn oil, yeast, vitamins, coconut oil, and vanilla, chocolate, or butterscotch flavoring. The low-calorie regimen enabled a dieter to lose ten pounds in a few weeks, without the trouble of meal preparation or counting calories. Later, Metrecal was sold in a premixed, liquid form that could be consumed right from the can. Mead Johnson made over $10 million selling Metrecal in the first two years. It was the forerunner of liquid diet products such as Slim-Fast.

The 1960s also witnessed the birth of Overeaters Anonymous (OA) and Weight Watchers. OA began as a support group modeled on the twelvestep physical, emotional, and spiritual recovery program used by Alcoholics Anonymous. In ''About Overeaters Anonymous'' (2008, http:// www.oa.org/about_oa.html), the OA notes that about sixtyfive hundred OA groups meet each week in sixty-five countries. In 1961 Jean Nidetch (1923-), an overweight house-wife in New York City, invited a few friends to her home to gain support for her efforts to diet and overcome an ''obses-sion for cookies.'' From this first meeting, the friends gathered weekly, offering one another encouragement and sharing advice and ideas. The weekly support meetings proved successful, providing motivation and encouragement for long-term weight loss. In 1963 Nidetch incorporated Weight Watchers, and hundreds of people turned out for its first meeting. Weight Watchers grew in both size and popularity, developing nutritious and convenient eating plans, promoting exercise, cookbooks, healthy prepared food, and a magazine. The company became so successful that in 1978 it was acquired by the Heinz company. Weight Watchers states in ''About Us: History and Philosophy'' (2008, http://www.weightwatchers.com/about/his/hello.aspx) that about fifty thousand Weight Watcher groups meet weekly.

Two best-selling diet books also debuted during the 1960s. The first was Herman Taller's Calories Don'tCount (1961), which told dieters to avoid carbohydrates and refined sugars and to eat a high-protein diet that included large quantities of unsaturated fat. The second was Irwin Maxwell Stillman with Samm Sinclair Baker's The Doctor's Quick Weight Loss Diet (1967), which instructed dieters to avoid carbohydrates altogether and to consume just meat, poultry, fish, cheese, eggs, and water. Even though Taller and Stillman and Baker were not the first to tout low-carbohydrate diets, they introduced the first modern high-protein weight-loss diets. Taller's career as a diet guru ended abruptly in 1967, when he was convicted of mail fraud for the sale of safflower capsules as weight-loss aids. Stillman and Baker, however, followed up their wildly successful first book with several other additional weight-loss titles, including The Doctor's Quick Teenage Diet (1971), one of the first diet books to address the needs of overweight adolescents. High-protein, low-carbohydrate diets washed down by liberal amounts of alcohol were also advocated by other books from the 1960s, including Gardener Jameson's The Drinking Man's Diet (1965) and Sidney Petrie's Martinis and Whipped Cream: The New Carbo-Cal Way to Lose Weight and Stay Slim (1966) and The Lazy Lady's Easy Diet: A Fast-Action Plan to Lose Weight Quickly for Sustained Slenderness and Youthful Attractiveness(1969).

During this same decade, chemically processed, non-nutritive sweeteners were marketed as calorie-and guilt-free substitutes that enabled dieters to enjoy many of their favorite sweet treats. Saccharin, which is three hundred times sweeter than sugar, was the first artificial sweetener to be widely used in diet foods and beverages. Other chemically processed, artificial, and nonnutritive sweeteners followed, including cyclamate, which was withdrawn from the U.S. market in 1969 because research findings in animals suggested that it might increase the risk of bladder cancer in humans. According to the National Cancer Institute, more recent animal studies fail to demonstrate that cyclamate is a carcinogen (a substance known to cause cancer) or a cocarcinogen (a substance that enhances the effect of a cancer-causing substance); regardless, cyclamate is not approved for commercial use as a food additive in the United States. Aspartame and acesulfame K were approved by the U.S. Food and Drug Administration (FDA) in 1981 and 1988, respectively. Sucralose, a noncaloric sweetener, was approved by the FDA for general use in 1999. Sucralose has gained popularity because it is derived from and tastes like sugar, has no aftertaste, does not promote tooth decay, and is deemed safe for use by pregnant women and diabetics, as well as by those in the general population who are trying to cut down on their sugar intake. In 2002 the FDA approved neotame, another nonnutritive sweetener, for use as a general-purpose sweetener. Neotame is approximately seven thousand to thirteen thousand times sweeter than sugar and has been approved for use in food products including baked goods, nonalcoholic beverages (including soft drinks), chewing gum, confections and frostings, frozen desserts, gelatins and puddings, jams and jellies, processed fruits and fruit juices, toppings, and syrups.

However, some researchers think sugar substitutes may sabotage dieters by interfering with the body's own innate ability to monitor calorie consumption based on a food's flavor—sweet or savory. Susan E. Swithers, Alicia Doerflinger, and Terry L. Davidson indicate in ''Consistent Relationships between Sensory Properties of Savory Snack Foods and Calories Influence Food Intake in Rats'' (International Journal of Obesity, vol. 30, 2006) that absent sensory clues about the relative caloric value of a food, both animals and humans may overeat and as a result become overweight.

In 1972 the cardiologist Robert C. Atkins (1930-2003) published Dr. Atkins' Diet Revolution, which provided a new explanation about how an extremely lowcarbohydrate diet targets insulin to promote weight loss. Atkins called insulin, the hormone that regulates blood sugar levels, a ''fat-producing hormone.'' He asserted that most overeaters are continually in a state of hyperinsulinism primed and ever-ready to convert excess carbohydrates to fat. As a result, they have excess circulating insulin, which primes the body to store fat. Atkins contended that when people with hyperinsulinism dieted to lose weight—especially when they reduced their fat intake and increased carbohydrate consumption—their efforts were doomed to fail. He claimed that dieters could alter their metabolisms and burn fat by inducing a state of ketosis (the accumulation of ketones from partly digested fats due to inadequate carbohydrate intake) that they monitored by testing their urine for the presence of ketones. Dieters who were tired of limiting portion size, weighing and measuring their foods, counting calories, and assiduously avoiding fatty foods such as steak, bacon, butter, cheese, and heavy cream embraced the low-carbohydrate diet with religious fervor.

The high-protein, low-carbohydrate diet not only was satisfying but also produced the immediate benefit of weight loss through water loss because the body flushes the waste products of protein digestion in the form of urine. Especially during the early weeks of dieting this additional weight loss delivered a psychological boost to dieters and provided the motivation to continue. As of 2008 many researchers and health professionals agreed with Atkins's premise that sharply limiting carbohydrate intake can help curb the appetite by maintaining even levels of insulin and preventing the insulin surges and blood sugar drops that may trigger hunger.

Even though Atkins and his devotees were celebrating weight loss, good health, and improved mood as a result of the low-carbohydrate diet, nutritionists and health professionals were countering by trumpeting the benefits of low-fat diets that were high in complex carbohydrates and fiber. Fat was demonized, and nutritionists pointed dieters to the USDA Food Guide Pyramid (http://www.mypyramid.gov/), which advised using fats sparingly. (The updated 2005 USDA Food Guide Pyramid continued to promote a low-fat diet and minimal use of fats and oils.) Critics of the low-carbohydrate regimen were concerned about the long-term health consequences of the high-fat diet and wondered if it might elevate cholesterol and triglyceride levels in people who by virtue of being overweight were already at increased risk for heart disease. There were also concerns that highprotein diets might cause kidney damage or bone loss over time. Rigorous research to compare the effectiveness and assess the health outcomes of low-carbohydrate and low-fat diets was not conducted until the late 1990s. Even though Atkins enjoyed tremendous celebrity, published a series of weight-loss books, and oversaw the sale of food products bearing his name, his significant contributions to the scientific understanding of nutrition and weight loss were not fully appreciated until the year preceding his death in 2003.

The 1970s also had its share of fad diets. Robert Linn's The Last Chance Diet—When Everything Else Has Failed (1976) advised a protein-sparing fast, which was so dangerously deficient in essential nutrients that several deaths were attributed to it. In The Complete Scarsdale Medical Diet Plus Dr. Tarnower's Lifetime Keep-Slim Program (1978), Herman Tarnower (1910-1980) advocated a fat-free, highprotein diet that allowed seven hundred calories per day.

At the close of the 1970s, Nathan Pritikin's (1915-1985) The Pritikin Program for Diet and Exercise (1979) championed a nearly fatfree diet that consisted of fresh and cooked fruits and vegetables, whole grains, breads and pasta, and small amounts of lean meat, fish, and poultry, in concert with daily aerobic exercise. Advocating heart health and fitness, in 1976 Pritikin opened the Pritikin Longevity Centers, where people could learn to modify not only their diets but also their lifestyles. Even though Pritikin's plan, which essentially eliminated fat from the diet, was considered by many health professionals too extreme to gain long-term adherents, Pritikin enjoyed as loyal a following as did Atkins.

During the 1980s Judy Mazel (1943-2007) resurrected the notion of specific food combinations as central to weight loss in The Beverly Hills Diet (1981). Mazel asserted that eating foods together, such as protein and carbohydrates, destroyed digestive enzymes and caused weight gain and poor digestion. Her diet featured an abundance of fruit, and some observers speculated that weight loss attributable to the diet resulted from the combined effects of caloric restriction and fluid loss resulting from diarrhea. Celebrity endorsements and the glamorous author's frequent media interviews stimulated interest in the diet.

In 1983 Jenny Craig (1932-) launched a weight-loss program that would become one of the world's two largest diet companies (the other being Weight Watchers). With 660 centers in North America, Australia, Guam, New Zealand, and Puerto Rico, the company (2007, http:// www.jennycraig.com/corporate/company/index.asp) that bears her name sells prepared foods, along with other weight-loss materials. The company offers telephone and online support and home delivery of food and support materials. In 2002 company founders Jenny Craig and Sid Craig sold their majority stake in the company to ACI Capital Co. and MidOcean Capital Partners, Inc., but retain 20% interest in the company.

The 1990s served up so-called new and revised versions of high-protein, high-fat, and low-carbohydrate diets and the low-fat diet as well as an update of Mazel's Beverly Hills diet. The cardiologist Dean Ornish (1953-) rekindled enthusiasm for low-fat eating with Eat More, Weigh Less: Dr. Dean Ornish's Life Choice Program for Losing Weight Safely While Eating Abundantly (1993). Atkins's 1999 update of Dr. Atkins' New Diet Revolution, which offered advice about how to achieve total wellness and weight loss, spent more than four years on the New York Times best-seller list and won over a new generation of dieters. Ornish's approach was directly opposed to Atkins's—he espoused the health benefits of vegetarianism and limiting dietary fat to just 10% of the total daily calories. However, both physicians took a holistic approach to health and weight loss, encouraging readers to engage in moderate exercise, foster social support, and reconnect with themselves to support their physical and emotional well-being.

Still, the diet that generated the most fanfare during the late 1990s was by the biochemist Barry Sears (1947-), who published The Zone: A Dietary Road Map (1995). Sears's high-protein, low-carbohydrate plan promised that by eating the correct ratio of protein, fat, and carbohydrates, dieters would lose weight permanently, avoid disease, enhance mental productivity, achieve maximum physical performance, balance and control insulin levels, and enter ''that mysterious but very real state in which the body and mind work together at their ultimate best.''

Since the turn of the twenty-first century, the fiery debate about the merits of low-carbohydrate and low-fat diets have intensified, with both sides citing scientific evidence to support the supremacy of one diet as the healthier and more effective weight-loss strategy. The cardiologist Arthur Agatston (1947-) offered a kind of compromise between the two regimens in The South Beach Diet: The Delicious, Doctor-Designed, FoolproofPlan for Fast and Healthy Weight Loss (2003). Agatston condemned simple carbohydrates, such as white flour and white sugar, citing them as the source of the continuous cravings that sabotage dieters, but did not eliminate complex carbohydrates from the diet. (Carbohydrates are classified as simple or complex. The classification depends on the chemical structure of the particular food source and reflects how quickly the sugar is digested and absorbed. Simple carbohydrates have one or two sugars, whereas complex carbohydrates have three or more.) Agatston's diet program was a modified carbohydrate plan that recommended plenty of high-fiber foods, lean proteins, and healthy fats, while cutting back on, but not entirely banishing, bread, rice, pastas, and fruits.

Marian Burros notes in ''Make That Steak a Bit Smaller, Atkins Advises Today's Dieters'' (New York Times, January 18, 2004) that in 2004 the Atkins organization, which had previously advised dieters to satisfy their appetites with ample quantities of steak, bacon, eggs, heavy cream, and other saturated fats, modified its position. According to Burros, Colette Heimowitz, the director of research and education for Atkins Nutritionals, advised health professionals and dieters that just 20% of a dieter's calories should come from saturated fat. However, she and other Atkins representatives asserted that this did not represent a change in the diet itself, simply a revision in communicating how the diet should be followed. Diet industry observers maintained that the warning to reduce the consumption of saturated fat was in direct response to the debut of the South Beach Diet and other low-carbohydrate regimens that called for less saturated fat. Heimowitz asserted that the change was made because ''we want physicians to feel comfortable with this diet, and we want people who are going to their physicians with this diet to feel comfortable.''

Americans' enthusiasm for low-carbohydrate diets cooled during 2004, and Atkins Nutritionals Inc., the company that catapulted low-carbohydrate diets into a national obsession, filed for bankruptcy court protection in August 2005. Many dieters abandoned low-carbohydrate diets in favor of regimens focused on the glycemic index (GI)—a ranking system for carbohydrates according to their immediate effect on blood glucose levels, in which a numerical value is assigned to a carbohydrate-rich food based on its average increase in blood glucose. The GI measures how fast and how much a food raises blood glucose levels. Weightloss diets based on the GI emphasize sharply restricting highindex foods and consuming primarily low-index foods.

Examples of foods with GI scores of seventy or above are cake, cookies, doughnuts, honey, French fries, rice, baked potato, and white bread. In contrast, lentils have a GI of twenty-nine, whereas broccoli, peanuts, and spinach have GIs of less than fifteen. Carbohydrates that break down slowly, such as whole-grain breads and cereals, beans, leafy greens, or cruciferous vegetables, generate slower glucose release into the blood stream and lower GI scores—fifty or less. Eating low GI foods supports weight loss by enhancing satiety (the feeling of fullness or satisfaction after eating) and thereby decreasing total food consumption.

In 2004 diet books that extolled the virtues of the low GI diet—including Michel Montignac's Eat Yourself Slim (1999), Rick Gallop's The G.I. Diet: The Easy, Healthy Way to Permanent Weight Loss (2003), and H. Leighton Steward et al.'s The New Sugar Busters (2003)—became quite popular. Proponents of low GI diets observed that the regimen not only produced weight loss but also improved overall health by reducing the risk for both Type 2 diabetes and cardiovascular disease.

Even though diet industry observers cannot predict the next craze, they are certain that a replacement for the low-carbohydrate diet will emerge. Contenders among the diets and diet books that debuted since 2004 include:

• French Women Don't Get Fat (2004) by Mireille Guiliano contends that the French are able to eat croissants and chocolate without becoming overweight because they take time to savor flavors and eat thoughtfully
• The Fat Resistance Diet (2005) by Leo Galland advises a diet rich in fish and other low-fat protein, vegetables, fruit, nuts, and green tea to help relieve inflammation and restore sensitivity to leptin, a hormone involved in fat metabolism that sends satiety signals to the brain
• The Perricone Weight Loss Diet: A Simple 3-Part Plan to Lose the Fat, the Wrinkles, and the Years (2005) by Nicholas Perricone recommends a diet composed of high-as opposed to low-GI foods and healthy (Omega-3-rich) versus unhealthy fats
• The 3-Hour Diet: How Low Carb Makes You Fat and Timing Will Sculpt You Slim (2005) by Jorge Cruise recommends eating frequently and timing meals and snacks to ''stoke the metabolism''
• The Diet Code: Revolutionary Weight-Loss Secrets from Da Vinci and the Golden Ratio (2006) by Stephen Lanzalotta promotes Mediterranean-style eating and emphasizes bread, fish, cheese, vegetables, meat, nuts, and wine
• The Total Wellbeing Diet (2006) by Manny Noakes details a low-carbohydrate, high-protein diet developed by scientists at the Commonwealth Scientific and Industrial Research Organization to help Australians lose weight
• The Rice Diet Cookbook: 150 Easy, Everyday Recipes and Inspirational Success Stories from the Rice Diet Community (2007) by Kitty Gurkin Rosati counters the low-carbohydrate diet trend with a low-salt diet featuring rice, vegetables, and fruit; this diet was developed in 1939 by Walter Kempner (1903-1997) at Duke University.

AMERICANS' DIETS

H. A. B. Hiza and L. Bente of the Center for Nutrition Policy and Promotion offer in Nutrient Content of the U.S. Food Supply, 1909-2004: A Summary Report (February 2007, http://www.cnpp.usda.gov/publications/foodsupply/FoodSupply1909-2004Report.pdf) historical data about the nutrients in the U.S. food supply and trends in Americans' diets. Table 5.1 shows the consumption of macronutrients (nutrients that the body uses in relatively large amounts: carbohydrates, fats, and proteins) in selected years from 1909 to 2004. Trends include:

• An increase of eight hundred calories per day from 1960-69 to 2004
• An increase of twenty grams of protein per day from 1960-69 to 2004
• An increase of thirty-six grams of fat consumption from 1960-69 to 2004

Table 5.2 shows Americans' decreased consumption of whole milk in favor of low-fat milk; increased consumption of cheese, legumes, nuts, and soy; and decreased use of grain products. It also documents the shift from butter to margarine use, a decline in total consumption of vegetables, and a dramatic increase in consumption of salad, cooking, and other edible oils.

Dietary Guidelines for Americans, 2005

Every five years the Dietary Guidelines for Americans are updated and revised to translate the most current scientific knowledge about individual nutrients and food components into dietary recommendations that may be adopted by the public. The recommendations are based on the preponderance of scientific evidence for reducing the risk of chronic disease and promoting health. Even though the recommendations focus on nutritional content, they recognize that a combination of poor diet and physical inactivity can lead to chronic diseases that include cardiovascular disease, Type 2 diabetes, hypertension (high blood pressure), osteoporosis, and certain cancers.

The U.S. Department of Health and Human Services and USDA's Dietary Guidelines for Americans, 2005 (January 2005, http://www.health.gov/dietaryguidelines/dga2005/document/pdf/DGA2005.pdf) characterizes a healthy diet as one that includes plenty of fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products, as well as lean meats, poultry, fish, beans, eggs, and nuts. A healthy diet is also low in saturated fats, trans fats (artificial fats created through the hydrogenation of oils, which solidifies the oil and limits the body's ability to regulate cholesterol), cholesterol, salt, and added sugars. Specific recommendations stipulate that fewer than 10% of calories should come from saturated fatty acids, and trans fatty acids, which are considered to be the most harmful to health, should be avoided. Cholesterol intake should be less than three hundred milligrams per day. Total fat intake should not exceed 20% to 35% of calories. Preferred fat sources are fish, nuts, and vegetable oils containing polyunsaturated and monounsaturated fatty acids. Lean, low-fat, or fat-free meats, poultry, dry beans, and milk or milk products are preferable to full-fat foods.

In general, the guidelines encourage most Americans to eat fewer calories, increase their physical activity, and choose nutrient-dense foods. They advocate increased consumption of fruits, vegetables, whole grains, and fat-free or low-fat milk and milk products. For example, two cups of fruit and two and a half cups of vegetables per day are recommended for a two-thousand-calorie diet, along with three or more servings of whole-grain products per day and three cups per day of fat-free or low-fat milk or equivalent milk products.

Two examples—the USDA Food Guide and the Dietary Approaches to Stop Hypertension (DASH) Eating Plan—offer instruction about how to allocate calories to various food groups. Table 5.3 shows the amounts of various food groups that are recommended each day or each week in the USDA Food Guide and in the DASH Eating Plan at the two-thousand-calorie level as well as the equivalent amounts for different food choices in each group. Acknowledging Americans' tendencies to eat out and eat while commuting, running errands, or working, the guidelines also offer tips for making healthy choices away from home. (See Table 5.4.)

The guidelines specifically address weight management, advising Americans ''to maintain body weight in a healthy range, balance calories from foods and beverages with calories expanded,'' and ''to prevent gradual weight gain over time, make small decreases in food and beverage calories and increase physical activity.'' For people who are overweight, the guidelines advise gradual, steady weight loss achieved by decreasing caloric consumption while maintaining sufficient nutrients and increasing physical activity. Parents of overweight children are counseled to reduce the rate of weight gain while children grow and develop and to consult a health-care provider before placing children on weight-reduction diets. Pregnant women are advised to gain weight as instructed by their health-care providers, and breastfeeding mothers are reassured that modest weight loss is safe and will not harm the development of nursing infants.

HOW WEIGHT-LOSS DIETS WORK

Research demonstrates that weight loss is associated with the length of the diet, pre-diet weight (people who are more overweight tend to lose more weight, more quickly than those who are only mildly overweight), and the number of calories consumed. Any diet that restricts caloric intake such that calories consumed are less than those expended will promote short-term weight loss. The key to weight loss through diet is adherence—if people do not stick to their diets, then they will not lose weight. More than a century ago, Banting, in describing the benefits of his low-carbohydrate diet, wrote that ''the great charms and comfort of this system are that its effects are palpable within a week of trial and creates a natural stimulus to persevere for a few weeks more.''

The successes achieved using regimens that restrict dieters to a single food or food group such as grapefruit, pineapple, or cabbage are probably in part attributable to the human hankering for variety. When limited to just one food, most dieters experience boredom—there is just no appeal to eating the same food at every meal, for days on end, so naturally less food is consumed. In addition, these diets generally rely on low-calorie foods, so that even if dieters were inspired to consume fifteen grapefruits per day, their total daily caloric consumption would be about twelve hundred calories, which is sufficient to produce weight loss for most people who are overweight.

Similarly, diets that involve stringent portion control effectively reduce calories to produce weight loss.

TABLE 5.4

Smart choices for eating out and on the go

It's important to make smart food choices and watch portion sizes wherever you are—at the grocery store, at work, in your favorite restaurant, or running errands. Try these tips:

• At the store, plan ahead by buying a variety of nutrient-rich foods for meals and snacks throughout the week.
• When grabbing lunch, have a sandwich on whole-grain bread and choose low-fat/ fat-free milk, water, or other drinks without added sugars.
• In a restaurant, opt for steamed, grilled, or broiled dishes instead of those that are fried or sautéed.
• On a long commute or shopping trip, pack some fresh fruit, cut-up vegetables, string cheese sticks, or a handful of unsalted nuts—to help you avoid impulsive, less healthful snack choices.

SOURCE: "Don't Give in When You Eat Out and Are on the Go," in Dietary Guidelines for Americans, 2005, 6th ed., U.S. Department of Health and Human Services and U.S. Department of Agriculture, January 2005, http://www.health.gov/dietaryguidelines/dga2005/document/media/OnTheGo.pdf (accessed October 22, 2007)

Low-Calorie Diets

Traditional dietary therapy for weight loss generally seeks to create a deficit of five hundred to one thousand calories per day with the intent of promoting weight loss of between one to two pounds per week. Low-calorie diets for men usually range from twelve hundred to sixteen hundred calories per day; for women low-calorie diets contain between one thousand and twelve hundred calories per day. Table 5.5 is an example of the recommended percentages of nutrients in a low-calorie diet that aims to decrease risk factors for hypertension and high cholesterol as well as cause weight loss.

The most successful low-calorie diets take individual food preferences into account to custom-tailor the diet. Table 5.6 and Table 5.7 show examples of how traditional American cuisine may be used to create a lowcalorie diet containing twelve hundred and sixteen hundred calories per day, respectively. Table 5.8 incorporates regional southern cuisine into a reduced-calorie diet. Table 5.9 illustrates how Asian-American cuisine may be adapted to twelve-hundred-and sixteen-hundred-calorieper-day diets, and Table 5.10 shows how Mexican-American cuisine may be adapted for low-calorie diets. Table 5.11 is a sample of a reduced-calorie diet that vegetarians who eat milk and eggs but no meat or fish can use to lose weight. Food exchanges, such as those shown in Table 5.12, enable dieters to enjoy a variety of foods in their reduced-calorie meals, which can prevent boredom and the tendency to abandon the diet.

Research reveals that reducing fat in the diet is an effective way to reduce calories and that when lowcalorie diets are combined with low-fat diets, better weight loss is achieved than through calorie reduction alone. Furthermore, even though very-low-calorie diets

that provide about five hundred calories per day have been demonstrated to produce greater initial weight loss than the low-calorie diets, the long-term weight loss is not different between the two regimens.

Low-Carbohydrate Diets

During 2004 and 2005 several rigorous research studies reported that low-carbohydrate diets were as effective, or even more effective, in producing short-term weight loss than low-fat diets. The low-carbohydrate diets owed much of their success to adherence—dieters were better able to stick with their diets, and as a result achieved better results. Another hypothesis about the success of low-carbohydrate regimens is that dieters do not feel as hungry as they do on other diets because protein is the most satisfying of the three macronutrients: carbohydrates, fats, and proteins.

The scientific premise of low-carbohydrate diets is that consuming certain carbohydrates can cause surges in blood sugar and insulin that not only stimulate appetite and weight gain but also may the increase risk for diabetes and heart disease. At first, low-carbohydrate diets viewed all carbohydrates as equally harmful. Increasingly, however, low-carbohydrate diets distinguished between simple and complex carbohydrates, which contain simple or complex sugars.

Examples of single sugars from foods include fructose, which is found in fruits, and galactose, which is found in milk products. Double sugars include lactose in dairy products; maltose, which is found in certain vegetables and in beer; and sucrose (table sugar). Examples of complex carbohydrates, which are often referred to as starches, include breads, cereals, legumes, brown rice, and pastas. Simple carbohydrates occur naturally in fruits, milk products, and vegetables; at the same time, these foods also contain vitamins and minerals. The simple carbohydrates most nutritionists call ''empty calories'' are the processed and refined sugars found in candy, table sugar, and sodas, as well as foods such as white flour, sugar, and polished white rice.

Besides distinguishing between simple and complex carbohydrates, low-carbohydrate regimens rely on a measure known as the glycemic index (GI), which ranks foods based on how rapidly their consumption raises blood glucose levels. The GI measures how much blood sugar increases over a period of two or three hours after a meal. Carbohydrate foods that break down quickly during digestion have the highest GI. The GI may be used to determine if a particular food will trigger the problematical ''carbohydrate-blood sugar-insulin cascade.'' High-GI foods are those that are rapidly digested and absorbed or transformed metabolically into glucose. These include refined starchy foods such as bread, cereal, pasta, and table sugar. In general, fiber-rich foods are low glycemic. Most vegetables, legumes, and fruits are low-GI foods.

The measurement of GI is a relatively recent practice. It began during the 1990s, following the discovery that specific carbohydrates such as potatoes and cornflakes raised blood sugar faster than others such as brown rice and oatmeal. Harvard University School of Public Health researchers used GI to calculate glycemic load—a measure that considers the food's GI and the amount of carbohydrate contained in a single serving. For example, many whole fruits, vegetables, and grains have low glycemic loads, which when consumed prompt a moderate rise in blood glucose and insulin. When the same fruits, vegetables, and grains are squeezed or pulverized into juice or flour, their glycemic load increases—effectively rendering them with the same high glycemic load of sugar water.

After consuming a meal with a high glycemic load, blood sugar rises higher and faster than it does after eating a meal with a low glycemic load. In an effort to recover from the resulting peaks and plummets, the brain transmits a hunger signal long before the next meal is due. Wildly fluctuating blood sugar and insulin may result in overeating, which in turn causes overweight. For people who are overweight or physically inactive, another potential danger of consuming foods with high glycemic loads is that they may already be insulin resistant, and overexertion of insulin-producing cells in the pancreas required to metabolize the high glycemic loads may ultimately exhaust their insulin-producing cells, leading to diabetes.

The proponents of low-carbohydrate diets observe that consuming foods with low glycemic loads stabilizes blood sugar and insulin to prevent the fluctuations that can cause overeating and may increase the risk for diabetes. They also assert that reliance on low-fat diets inadvertently led to diets that were high in simple carbohydrates and indirectly promoted the observed increase in overweight and diabetes in the United States.

Low-Fat Diets

Low-fat diets reduce caloric intake by reducing fat consumption. Fat has nine calories per gram, whereas protein and carbohydrates have four calories per gram. These diets rely on the high-fiber content of complex carbohydrates to satisfy dieters. High-fiber foods also slow the absorption of carbohydrates, so they do not provoke a rapid rise in blood sugar and insulin.

Table 5.13 shows some of the food substitutions that may be made to reduce the dietary fat content. Besides making substitutions, many fat-free or low-fat food products are available—from fat-free frozen desserts to reduced-fat peanut butter. However, dieters are often cautioned that fat-free or reduced-fat foods are not calorie-free and that their consumption will not result in weight loss when more of the reduced-fat foods are consumed than would be eaten of the full-fat versions. For example, eating twice as many baked tortilla chips would actually result in higher caloric intake than a single serving of regular tortilla chips. (See Table 5.14.)

Low-Fat versus Low-Carbohydrate Diets

In the absence of rigorous scientific research and studies demonstrating the long-term safety and effectiveness of low-carbohydrate and low-fat diets, many investigators and health professionals hesitate to proclaim one diet's superiority over all others. There is consensus that even though some diets may produce greater initial weight loss, most perform similarly over time.

In ''Efficacy and Safety of Low-Carbohydrate Diets: A Systematic Review'' (Journal of the American Medical Association, vol. 289, no. 14, April 9, 2003), Dena M. Bravata et al. report the results of their analysis of data about diet-induced changes in weight, serum lipids, fasting serum glucose and fasting serum insulin levels, and blood pressure among adults using low-carbohydrate diets. The investigators undertook the research in response to concerns about low carbohydrates expressed by the American Dietetic Association and the American Heart Association. Both organizations had warned that lowcarbohydrate diets may lead to abnormal metabolic functioning that in turn may prompt serious medical consequences, particularly for participants with cardiovascular disease, Type 2 diabetes mellitus, hyperlipidemia (an excess of fats called lipids, chiefly cholesterol and triglycerides, in the blood), or hypertension. Specifically, it has been cautioned that low-carbohydrate diets cause the accumulation of ketones, which may result in abnormal metabolism of insulin, impaired liver and kidney function, and salt and water depletion that may cause postural hypotension (sudden drop in blood pressure when rising from sitting) as well as fatigue, constipation, and kidney stones. It has also been posited that excessive consumption of animal proteins and fats may promote hyperlipidemia and that higher dietary protein loads may impair kidney function.

Bravata et al. find that diets that restricted calorie intake and were longer in duration were associated with weight loss. They also observe that when lowercarbohydrate diets resulted in weight loss, it was likely because of the restriction of caloric intake and longer duration rather than changes in carbohydrate intake. The investigators note that at least in the short term, lowcarbohydrate diets were not associated with the anticipated adverse effects on lipid levels, glucose levels, or blood pressure. Furthermore, their findings suggest that people without diabetes tolerated a lower-carbohydrate diet better than higher-carbohydrate alternatives and that this diet may be an effective means of achieving short-term weight loss without significant adverse effects on serum lipid levels, glycemic control, or blood pressure. They caution, however, that there is still inadequate evidence to recommend or condemn the use of low-carbohydrate diets among people with diabetes or for long-term use.

According to Peggy Peck, in ''Four Popular Diets Equally Effective for Weight Loss'' (Medscape Today, November 10, 2003, http://www.medscape.com/viewarticle/464193), Michael L. Dansinger et al. compared the effectiveness of four popular diets: Atkins (low carbohydrates), the Zone (moderate carbohydrates), Ornish (low-fat vegetarian), and Weight Watchers (moderate fat). Study participants were asked to follow the diets they were given as best they could for two months, and they were given official diet cookbooks and assigned to small group classes for diet education. For the remaining ten months, the participants were told to follow their assigned diets ''to whatever extent they wanted.'' Dansinger et al. report that nearly one-quarter (22%) of the participants had dropped out of each diet after just two months, and by twelve months half of the participants assigned to low-carbohydrate or low-fat vegetarian diets had dropped out, as had 35% of participants assigned to the moderate carbohydrates and moderate fat diets. For those participants who adhered, weight loss and reduction in cardiac risk scores as measured by reductions in LDL cholesterol and insulin levels were comparable for participants on the low-carbohydrate, moderate-carbohydrate, and moderate-fat plans. According to the study, the Ornish diet ''does not increase HDL, while the other diets do achieve significant increases in HDL.''

Dansinger et al. conclude that their research ''demonstrated that all these diets work.'' They also reiterate the importance of tailoring the selection of a weight-loss diet to ensure adherence, asserting ''that means that physicians can work with patients to select the diet that is best suited to the patient. For example, if you have a patient who likes meat, it is unlikely that he or she will comply with the Ornish diet.''

In 2004 two published studies reaffirmed the safety and efficacy of low-carbohydrate diets. In the first study, ''A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet to Treat Obesity and Hyperlipidemia: A Randomized, Controlled Trial'' (Annals of Internal Medicine, vol. 140, no. 10, May 18, 2004), William Yancy Jr. et al. assigned 120 study participants to a low-carbohydrate, high-protein diet or a low-fat, low-cholesterol, lowcalorie diet. The low-carbohydrate group was allowed unlimited calories, animal foods (meat, fowl, fish, and shellfish), and eggs, as well as four ounces of hard cheese, two cups of salad vegetables (lettuce, spinach, or celery), and one cup of low-carbohydrate vegetables (broccoli, cauliflower, or squash). The low-fat, lowcholesterol, low-calorie group consumed less than 30% of daily caloric intake from fat, less than 10% of calories from saturated fat, and less than three hundred milligrams of cholesterol daily. After six months, weight loss was greater in the low-carbohydrate diet group than in the low-fat diet group. Compared to the low-fat diet group, the low-carbohydrate diet group had greater decreases in serum triglyceride levels and greater increases in HDL cholesterol levels.

In the second study, ''A Low-Carbohydrate, Ketogenic Diet versus a Low-Fat Diet to Treat Obesity and Hyperlipidemia: A Randomized, Controlled Trial'' (Annals of Internal Medicine, vol. 140, no. 10, May 18, 2004), William Yancy Jr. et al. assigned 132 obese adults to either restrict carbohydrate intake to less than thirty grams per day (low-carbohydrate diet) or to restrict caloric intake by five hundred calories per day with less than 30% of calories from fat (conventional diet). After one year, weight loss was greater in the low-carbohydrate diet group, and Yancy et al. found that the low-carbohydrate diet group fared better in terms of a greater decrease in triglyceride levels.

In another study, Y. Wady Aude et al. confirm in ''The National Cholesterol Education Program Diet vs. a Diet Lower in Carbohydrates and Higher in Protein and Monounsaturated Fat'' (Archives of Internal Medicine, vol. 164, no. 19, October 25, 2004) that modified lowcarbohydrate diets produced greater weight loss than the U.S. National Cholesterol Education Program diet, which replaces saturated fat with carbohydrates.

However, the article ''Study: Low-Fat Tops Low-Carb for Keeping Pounds Off'' (USA Today, November 16, 2004) notes that Suzanne Phelan of Brown Medical School asserted at a meeting of the North American Association for the Study of Obesity that low-fat diets produce better long-term weight loss than low-carbohydrate diets. She and her colleagues studied twenty-seven hundred people who entered the National Weight Control Registry, which records successful efforts to lose at least thirty pounds and maintain the loss for at least one year. All the subjects reported eating about fourteen hundred calories per day, but the portion derived from fat rose from 24% in 1995 to more than 29% in 2003, whereas the portion from carbohydrates fell, from 56% to 49%. The number who were on low-carbohydrate diets (less than ninety grams per day) rose from 6% to 17% during this same period.

Even though the type of diet—low fat or low carbohydrate—made no difference in how people lost weight initially, those who increased their fat intake over a year regained the most weight. The researchers noted that the subjects ate fewer carbohydrates, because the amount of protein in their diets remained the same. As a result, the researchers concluded that the minority of successful dieters use low-carbohydrate regimes.

Even though there is no single winner in the diet wars, research dispels some fears about the safety and effectiveness of the low-carbohydrate diet. Low-carbohydrate diets appear to be safe and effective in the short term, but longterm outcomes are still unclear. Some results suggest that higher protein and fat intakes lead to lower total caloric intake by producing earlier satiety, but these diets have not been shown to alter fundamental eating behaviors, nor have they demonstrated, as many of their proponents argue, the ability to modify caloric balance such that weight loss persists when more calories are consumed than expended.

Finally, in ''Comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets for Weight Loss and Heart Disease Risk Reduction'' (Journal of the American Medical Association, vol. 293, no. 1, January 5, 2005), Michael L. Dansinger et al. assert that adherence to a diet for one year, rather than the specific type of diet, is the single most important determinant of weight loss and reduction of risk of cardiovascular disease. The researchers find that the amount of weight lost was associated with the level of dietary adherence but not with diet type. Dansinger et al. conclude that ''one way to improve dietary adherence rates in clinical practice may be to use a broad spectrum of diet options, to better match individual patient food preferences, lifestyles, and cardiovascular risk profiles. . . . Our findings challenge the concept that one type of diet is best for everybody and that alternative diets can be disregarded. Likewise, our findings do not support the notion that very low carbohydrate diets are better than standard diets, despite recent evidence to the contrary.''

Gabrielle M. Turner-McGrievy, Neal D. Barnard, and Anthony R. Scialli indicate in ''A Two-Year Randomized Weight Loss Trial Comparing a Vegan Diet to a More Moderate Low-Fat Diet'' (Obesity, vol. 15, 2007), a weight-loss maintenance study that compared vegan diets to the National Cholesterol Education Program (NCEP) diet, a low-calorie, low-fat diet that is high in carbohydrates, that a vegan diet was associated with significantly greater weight loss than the NCEP diet after the one-and two-year follow-ups.