Evidence for Success of Exercise in Weight Loss and Control

One can evaluate the relation of exercise to body weight control from several perspectives. Physiologists and endocrinologists may be interested in the effect of exercise on basal metabolic rate, fat cell size and distribution, and dietary-induced thermogenesis, whereas psychologists may be concerned about the possible effect of exercise on body image and self-concept, feelings of well-being, and adherence to an exercise plan. Clinicians may focus their attention on the role of exercise in ameliorating disease risk. The perspective taken here is that of epidemiology and public health, with an emphasis on the relation of exercise to weight control and on morbidity and mortality in overweight or obese persons. The topics presented here include brief discussions of the role of exercise in the prevention of weight gain, the effect of exercise on weight loss and maintenance, and exercise and health risks in overweight persons. Articles selected for this brief review included recent, large, population-based, prospective studies of weight gain in active and sedentary persons; comprehensive review articles of exercise and weight loss; recent large, well-controlled, randomized clinical trials on exercise and weight loss and maintenance; recent representative studies on exercise and body fat distribution; and the most recent population-based, prospective studies on the relation of activity or fitness on morbidity and mortality in overweight men and women. The studies were selected because they contained clear definitions of activity and fitness assessment, relatively complete follow-up, and sound methods (random assignment in the clinical trials and prospective design in the population-based studies). Exercise and the Prevention of Overweight Prevention of overweight or obesity depends on long-term maintenance of an isocaloric state. The two principal components of caloric balance are energy intake and energy expenditure. Cross-sectional surveys show that obese persons probably eat fewer calories, or perhaps the same amount of calories, as do persons of normal weight [1, 2]. No convincing evidence exists to suggest that obesity is caused by an excessively high absolute caloric intake. Cross-sectional studies show that caloric expenditure in the obese is less than, or perhaps equal to, expenditure in persons of normal weight [1, 2]. Male and female runners report caloric intakes (that are 500 to 600 kcal/d) higher than those of sedentary community controls, yet the runners remain far leaner than their sedentary counterparts [3]. Interpretation of these cross-sectional data is difficult and is complicated by variation in measurement techniques (caloric intake and expenditure are sometimes reported as total calories and sometimes as calories per kilogram of body weight). The role of exercise in the prevention of overweight is clarified somewhat by new data from prospective population studies. Rissanen and colleagues [4] described the determinants of weight gain in a representative cohort of 6165 women and 6504 men 25 to 64 years old in Finland. These persons were examined in mobile health clinics from 1966 to 1972 and again from 1973 to 1976 (average duration of follow-up, 5.7 years). Significant weight gain ( 5 kg in 5 years) occurred in 15.1% of the women and in 17.5% of the men. Adjusted relative risks with 95% CIs for significant weight gain across leisure-time physical activity categories (frequent, occasional, rare) were 1.0, 1.5 (95% CI, 1.1 to 2.0), and 1.6 (CI, 1.2 to 2.2) in women and 1.0, 1.5 (CI, 1.2 to 2.0), and 1.9 (CI, 1.5 to 2.3) in men for the three activity categories, respectively. These relative risks were adjusted for smoking behavior, alcohol and coffee intake, health status, and sociodemographic factors. These investigators also reported results from a later survey (1978 to 1980) of a representative sample of 5673 Finnish men and women 30 to 64 years old. The prevalence of distinct overweight (body mass index [BMI] 30 kg/m2) was 15.8% for women and 11.3% for men. Adjusted relative risks for distinct overweight were greater than 2.0 for both men and women when rare and frequent leisure-time physical activity categories were compared. Williamson and colleagues [5] reported on 10-year weight gain in 3515 men and 5810 women in the National Health and Nutrition Survey-I Epidemiologic Follow-up Study. Recreational physical activity was assessed at baseline and at follow-up by questionnaire, and weight was measured at both examinations. Persons classified as having low levels of physical activity at both assessments were more likely to have a weight gain of more than 13 kg than were persons classified as having high levels of physical activity at both examinations. The relative risks for weight gain for low compared with high activity were 2.3 (CI, 0.9 to 5.8) in men and 7.1 (CI, 2.2 to 23.3) in women. This study provides the strongest evidence currently available that remaining physically active may help to prevent age-related weight gain. We evaluated possible determinants of weight gain in 10 221 men at high risk for coronary heart disease who were participants in the Multiple Risk Factor Intervention Trial (MRFIT) (Unpublished data). Weight gain was defined as an increase in body weight (> 5% of baseline weight) over the course of the study (6 or 7 years). Multiple regression models showed that weight gain was positively associated with initial weight, smoking cessation, relapse after smoking cessation, attempts to quit smoking, and initiation of diuretic medication during the first year of the trial. Baseline physical activity, an increase in activity level during the trial, and age were inversely associated with weight gain. Men who were sedentary at baseline or who did not increase their activity during the trial also were more likely to have greater amounts of weight fluctuation during the course of the study. Effectiveness of Exercise in Weight Loss Weight-loss results when a person maintains a negative energy balance for a period of time. The usefulness of increased physical activity in attempts to lose weight is controversial. Most controlled exercise training studies show modest weight loss (usually 2 to 3 kg) in the treated group compared with controls [2]. Nonetheless, some reviewers conclude that exercise alone appears largely ineffective regarding weight loss [6], and others suggest that exercise alone may be useful [2]. There are factors that may contribute to the confusion surrounding this issue. First, the degree of obesity is probably important. A moderately overweight person (90 kg, for example) who loses 5 kg in a walking program might be considered a treatment success. On the other hand, a 5-kg loss due to an exercise program for a person who weighs 120 kg could be considered inconsequential. A second issue is the length of the study period [2]. Many overweight or obese persons are so unfit that they cannot sustain caloric expenditure sufficient to achieve or maintain a negative energy balance. A sedentary, obese person may require several months to become fit enough to exercise at a level that burns a significant number of calories [7]. Finally, a serious methodologic limitation results from the fact that some of the exercise studies did not evaluate diet, just as many diet studies did not assess exercise habits. King and Tribble [2] recently reviewed studies on exercise and weight loss. Eleven of these studies included an intervention of exercise plus diet. The average weight loss for patients in these studies after the acute intervention phase was 8.5 kg. All these studies also had a diet only group in which the average weight loss was 6.7 kg. The modest additional weight loss of slightly less than 2 kg is consistent with the findings of an earlier extensive review of exercise alone on weight loss by Wilmore [8]. He concluded that exercise training results in modest decreases in total and fat weight as well as in a small increase in lean body weight. The average reduction in the percentage of body fat in the 55 studies reviewed by Wilmore was 1.6%. Wood and colleagues [9] reported a recent study (not included in King's review) in which diet alone and diet plus exercise were evaluated in a large (119 men and 112 women), well-controlled, 1-year randomized trial. The results of this trial are shown in Table 1. The groups combining diet with exercise lost more weight and more fat and had a greater improvement in the abdomen-to-hip ratio than did the groups using diet alone, although the differences were not statistically significant in women. Patients combining diet with exercise achieved this greater success despite having a slightly smaller energy intake deficit. Wood and colleagues also found that the participants using diet plus exercise had greater improvements in their lipoprotein profiles. Table 1. Body Composition, Fitness, and Energy Intake Changes after 1 Year in Men and Women* Weight alone may not be as important as the distribution of body fat in the prediction of disease risk. Several recent, population-based studies have shown that physically active men and women have lower (more favorable) waist-to-hip ratios than do their sedentary counterparts [1013]. This finding is supported by the data from Wood and colleagues [9] shown in Table 1. In summary, available studies suggest that exercise alone promotes weight loss, but the amount of weight that can be lost quickly is probably less than that achieved through dieting alone. The addition of exercise to caloric restriction appears to increase the amount of weight loss over either treatment used separately. Effectiveness of Exercise in Weight Maintenance Long-term maintenance of weight loss is an important factor. King [2] also reviewed long-term weight loss after exercise alone, diet alone, or diet plus exercise. Although differences in study designs, samples, duration of intervention, and duration of follow-up exist, avera