PHYSICAL ACTIVITY AND NUTRITION

PHYSICAL ACTIVITY AND NUTRITION. Regular physical activity and proper nutrition are critical for optimal health. Both have been linked to reducing the risk of a large number of common chronic diseases. In most cases, it is difficult to separate the roles these two factors play in decreasing disease risk. The importance of both of these factors is highlighted by the United States government in the 2000 Dietary Guidelines for Americans published by the U.S. Department of Health and Human Services and the U.S. Department of Agriculture. The guidelines' recommendations include aiming for a healthy weight; being physically active each day; following the food guide pyramid; eating a variety of grains, fruits, and vegetables each day; choosing a diet low in saturated fat and cholesterol and moderate in total fat; consuming less sugar and salt; drinking alcohol only in moderation, if at all; and keeping food safe to eat. These suggestions can greatly reduce disease risk. The role of physical activity in particular is a primary focus in the article that follows.

Benefits of Physical Activity

The 1996 Surgeon General's report, Physical Activity and Health, summarized many of the advantages obtained through participation in regular physical activity. It should be noted that these benefits can be acquired through a broad variety of activities; thus, the terms "exercise" and "physical activity" should not be limited solely to describing activities that are specifically designed to enhance fitness. Activities considered beneficial to health include structured exercise (e.g., walking, running, cycling, weight lifting, etc.), participation in sports, leisure-time and recreational pursuits, occupational duties, and other forms of movement.

Jeremy Morris and colleagues (1953) were among the earliest researchers to suggest that physical activity confers benefits to health. In their study, the rate of coronary events (i.e., angina pectoris, thrombosis, death) for double-decker bus and tram conductors in London was compared to that of their more sedentary driving counterparts. Conductors had an overall lower incidence of coronary events and mortality than drivers, and the authors suggested that the greater level of physical activity that results from conducting versus driving might be the explanation. Many other investigators have since confirmed the notion that being more active reduces risk of heart disease and premature death, as well as many other common health problems.

Many of the health benefits of exercise are probably indirect, through control of body weight; however, physical activity alone also appears to be helpful. A recent review of the literature by Stephen Blair and Suzanne Brodney (1999) concluded that the current understanding of the importance of exercise to health suggests that physical activity reduces health risks that are usually associated with overweight and obesity, even in those who remain obese. Furthermore, they concluded that inactivity and low cardiorespiratory fitness increase the risk of premature death so that the risk is equal to being overweight or obese. Thus, physical activity is essential for optimal health regardless of body weight.

The reasons for the apparent health benefits of physical activity with regard to multiple disease conditions have been addressed by many studies. Although all of the mechanisms are not yet completely understood, several physiological effects of exercise have been observed and may be responsible. It is likely that improved cardiac and musculoskeletal function account for many of the benefits. Additionally, physical activity alters metabolic and hormonal processes that may modify disease risk, and activity also appears to be involved in improving immune function.

Physical Activity Guidelines

Quantifying the optimal level of physical activity required to reduce the risk of disease has proven difficult. However, leading organizations have provided recommendations for minimal levels of activity. Exercise guidelines from the American College of Sports Medicine (1998) for cardiorespiratory fitness, muscular strength and endurance, flexibility, and body composition are provided in the sidebar "American College Sports Medicine Guidelines for Fitness." Additionally, the Surgeon General's report (1996) recommends that people of all ages include a minimum of thirty minutes of physical activity of moderate intensity (such as brisk walking) on most, if not all, days of the week. Furthermore, two objectives of Healthy People 2010 (2000), a set of health objectives developed by the United States Department of Health and Human Services, are, first, to increase the proportion of adolescents who engage in vigorous physical activity that promotes cardiorespiratory fitness three or more days per week for twenty or more minutes per occasion, and, second, to increase the proportion of adults who engage regularly, preferably daily, in moderate physical activity for at least thirty minutes per day.

Although numerous positive effects of physical activity exist, participation in strenuous exercise and work is not completely without risk in all circumstances. Primary risks include musculoskeletal injuries and cardiovascular events such as heart attacks. To avoid musculoskeletal injuries, it is most commonly recommended when beginning a physical activity program that the participant gradually increase the duration and intensity of the routine. Although physical exertion can result in a cardiovascular event, this is a rare occurrence in the healthy population. However, the Surgeon General's report (1996) suggests that adults with chronic diseases, such as heart disease, diabetes, or obesity, consult a physician before starting a program of physical activity, as should men over forty years of age and women over fifty years of age who plan to start a "vigorous" exercise program.

Conclusions

Many beneficial effects of diet and exercise are known; however, the interactive effects of the two are less understood. The relative importance of these lifestyle choices on various risk factors for chronic diseases is not clear. In some cases, physical activity and proper nutrition effects may be additive. In other cases, a synergistic effect of the two may exist. Additionally, it is also possible that for some risk factors, high levels of physical activity may even negate the adverse effects that a poor diet typically has on more sedentary individuals. For example, regular strenuous exercise appears to abolish the cholesterol-raising effects of a diet high in saturated fat. Clearly, the interaction between physical activity and nutrition relative to health benefits deserves considerable investigation now and in the future, so that we may optimally manage risk for chronic diseases.

See also Assessment of Nutritional Status ; Dietary Assessment ; Dietary Guidelines ; Dietary Systems ; Dietetics ; Fats ; Food Politics: U.S. ; Health and Disease ; Malnutrition ; Nutrients ; Nutrition ; Nutritionists ; Obesity .

BIBLIOGRAPHY

Blair, Steven N., and Suzanne Brodney. "Effects of Physical Activity and Obesity on Morbidity and Mortality: Current Evidence and Research Issues." Medicine and Science in Sports and Exercise 31 (1999): S646–S662.

Healthy People 2010. U.S. Department of Health and Human Services, Washington, D.C., 2000.

Morris, J. N., J. A. Heady, P. A. B. Raffle, C. G. Roberts, and J. W. Parks. "Coronary Heart Disease and Physical Activity of Work." The Lancet 2 (1953): 1053–1057, 1111–1120.

Physical Activity and Health: A Report of the Surgeon General. U.S. Department of Health and Human Services, Washington, D.C., 1996.

Pollock, Michael L., Glenn A. Gaesser, James D. Butcher, et al. "ACSM Position Stand on the Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Adults." Medicine and Science in Sports and Exercise 30 (1998): 975–991.

Mark Kern

Benefits of Regular Physical Activity

• Decreases the risk of premature death
• Decreases the risk of dying prematurely from coronary heart disease
• Decreases the risk of Type II diabetes mellitus
• Decreases the risk of hypertension
• Helps reduce blood pressure in people with hypertension
• Decreases the risk of colon cancer
• Decreases feelings of depression and anxiety
• Helps control body weight
• Helps build and maintain healthy bones, muscles, and joints
• Improves strength in older adults and decreases their risk of falling
• Promotes psychological well-being

American College of Sports Medicine Guidelines for Fitness

Cardiorespiratory Fitness and Body Composition

1. Frequency of training: 3–5 days per week.
2. Intensity of training: 55/65 percent–90 percent of maximum heart rate. The lower intensity values (55–65 percent) are most applicable to individuals who are quite unfit.
3. Duration of training: 20–60 minutes of continuous or intermittent (minimum of 10-minute bouts accumulated throughout the day) aerobic activity. Duration is dependent on the intensity of the activity; thus, lower-intensity activity should be conducted over a longer period of time (30 minutes or more), and, conversely, individuals training at higher levels of intensity should train at least 20 minutes or longer.
4. Mode of activity: Any activity that uses large muscle groups, that can be maintained continuously, and that is rhythmical and aerobic in nature, e.g., walking-hiking, running-jogging, cycling-bicycling, cross-country skiing, aerobic dance or group exercise, rope skipping, rowing, stair climbing, swimming, skating, and various endurance game activities or some combination thereof.

Muscular Strength and Endurance, Body Composition, and Flexibility

1. Resistance training: Resistance training should be an integral part of an adult fitness program and should be of a sufficient intensity to enhance strength and muscular endurance, and to maintain fat-free mass. Resistance training should be progressive in nature and individualized, and should provide a stimulus to all the major muscle groups. One set of 8–10 exercises that conditions the major muscle groups 2–3 days per week is recommended. Multiple-set regimens may provide greater benefits if time allows. Most persons should complete 8–12 repetitions of each exercise; however, for older and more frail persons (approximately 50 to 60 years of age and above), 10–15 repetitions may be more appropriate.
2. Flexibility training: Flexibility exercises should be incorporated into the overall fitness program sufficient to develop and maintain range of motion. These exercises should stretch the major muscle groups and be performed a minimum of 2–3 days per week.