Physical activity in the prevention and treatment of obesity and its comorbidities: evidence report of independent panel to assess the role of physical activity in the treatment of obesity and its comorbidities

On February 4–6, 1999,the American College of Sports Medicine sponsored a scientific roundtable on the role of physical activity in the prevention and treatment of obesity and its comorbidities. The purpose of the conference was to provide an evidence-based review of the current state of knowledge on physical activity as a modality for coping with the "epidemic" of obesity occurring in the United States and other nations (1,5). Participants of the conference were requested to review existing literature and to classify available data according to accepted evidence-based categories. The categories employed are those outlined in the recent Clinical Guidelines on the Identification, Evaluation, and Treatment of Obesity in Adults reported by a task force of the Obesity Education Initiative (OEI) of the National Heart Lung and Blood Institute (NHLBI) (2) (Table 1). Table 1: Categories of evidence.A particular goal of this roundtable was to review randomized clinical trials (RCT) that provide evidence in Categories A and B. Unfortunately, there are a limited number of RCT of physical activity in obese populations. On the other hand, the field is rich in observational data and studies in human physiology and behavior (Category C). A sizable portion of the Category C evidence derives from large and replicated studies and provides a considerable base upon which recommendations can be made. Such recommendations indeed are set forth in the OEI report (2), the NIH Consensus Conference Statement on Physical Activity and Cardiovascular Health (December 18–20, 1995) (3), and the Report of the Surgeon General on Physical Activity and Health (4). The current roundtable aimed to extend these previous reports by examining prior and new publications in more depth and by categorizing evidence more precisely as to type and strength. The manuscripts upon which presentations and the current panel report are based are being published concurrently in Medicine and Science in Sports and Exercise. The glossary of key terms used in the current report are those derived from the Surgeon General's report on physical activity and health (4) (Table 2). Table 2: Glossary of terms.BACKGROUND Prevalence and trends in overweight and obesity. The most recent National Health and Nutritional Examination Survey (1988–1994) (NHANES III) (1) revealed that 54.9% of American adults are overweight or obese (see Table 3 for OEI classification of overweight and obesity). Since 1960, overweight and obesity have increased across all ages, genders, and racial/ethnic groups. Prevalence in the obese category has increased by about 10%. Not only has the overall distribution of BMI shifted to higher levels, but the distribution has become even more skewed toward the high end. In the recent survey (1), the highest prevalence of obesity was found among non-Hispanic black women, Mexican-American women, Mexican-American men, and among less well-educated and low income people. Table 3: Classification of overweight and obesity by BMI.The recent OEI report (2) emphasized that waist circumference is a good indicator of abdominal obesity, which at BMI levels ≤ 35 kg·m−2 is correlated more closely with the comorbidities of overweight than is BMI (see Table 4 for OEI classification of disease risk according to waist circumference). Cross-sectional epidemiological data are not available to define the prevalence of abdominal obesity in the population; neither are data available to correlate waist circumference with comorbidities in the whole population. Such data would add significantly to our understanding of the metabolic consequences of overweight. Table 4: Disease riska relative to normal weight and waist circumference.Prevalence and trends in physical activity. The 1996 Behavioral Risk Factor Survey (BRFSS) reveals a high prevalence of physical inactivity among American adults and high school students (see Table 5 for the classification of physical activity used in the Surgeon General's report on physical activity). Adolescents are more active than adults; 64% of high school students report participating in vigorous hard or very hard) activity for at least 20 min on 3 or more days per week. Boys engage in physical activity more than girls, and whites in general more than in blacks or Hispanics. Physical activity declines at higher grades in school, especially among girls. Among adults, only 28% of men and women achieve moderate or vigorous levels of physical activity. Further, 27% of men and 31% of women report no regular physical activity outside of work. Educational level is a factor in exercise pattern. Less than 20% of college graduates report being inactive, whereas nearly half the population with a high school education are inactive. Black and Hispanic men and women are less active than white men and women. In spite of long-term societal trends in activity patterns, these have not been assessed quantitatively; moreover, leisure-time activity apparently has not changed much over the recent decades. Future surveys might well examine the impact of changes in activity patterns at work and at home, and in active and passive leisure time activities (i.e., less active recreation during and after school and more television viewing, computer work, and playing video games). Table 5: Classification of physical activity intensity, based on physical activity lasting up to 60 min.The economic costs of obesity and inactivity. The medical costs of obesity and physical inactivity can be estimated from the strengths of their associations with various diseases—coronary heart disease, diabetes, gallstone disease—and comorbid risk factors. The direct costs of a lack of physical activity, defined conservatively as absence of leisure-time physical activity, are approximately 24 billion dollars, or 2.4% of the United States health care expenditures. Direct costs for obesity defined as a body mass index (BMI) greater than 30 kg·m−2, in 1995 dollars, totals 70 billion dollars. The costs of inactivity are independent of obesity and the costs of obesity are independent of those due to a lack of physical activity. Overall, the direct costs of inactivity and obesity are estimated to consume some 9.4% of national health care expenditures in the United States. Determinants of overweight and obesity. The high and increasing prevalence of overweight and obesity must be due in large part to environmental factors. Development of obesity requires that energy intake exceed energy expenditure; maintenance of obesity demands a higher energy input, or a lower energy expenditure or both, than needed for a healthier weight. Factors affecting both intake and expenditure of energy probably play a role in the causation and maintenance of obesity. Societal trends go against reducing energy intake as well as against increasing energy expenditure. A relatively high intake of energy is driven by a food supply that contains readily available, energy-dense foods, served in large portions. Energy expenditure is lowered by progressively lesser amounts of physical activity required at work and at leisure. Most energy expenditure is obligatory, determined by resting metabolic rate and the thermic response to food intake, but physical activity must not be discounted in the equation for total energy expenditure. Even in the absence of occupations or recreations that consume large amounts of energy, regular physical activity offers a means to lessen the severity of overweight and obesity in the population. A sustained increment in energy expenditure of 200 kcal·d−1 through increased physical activity would reduce body weight by about 5 kg over a period of 6 months to 1 yr, assuming no increase in food consumption. Unfortunately, any weight loss achieved by moderate physical activity can be easily reversed by small compensatory increases in food intake. Measurements of body habitus and energy parameters. If the role of physical activity in the causation or treatment of obesity is to be placed on a quantitative basis, accurate measurements must be made of body composition, energy intake and expenditure, and levels of physical activity. Methods for measurements in each of these areas are improving but still have significant limitations. Significant strides have been made in measurements of body composition—total body fat, body fat distribution, lean body mass, and muscle mass. Several of these techniques are increasingly being used in epidemiological studies, but the most sophisticated measurements can be costly. Despite the advantage of being safe enough for use in children and pregnancy, the latter are too laborious and costly for use in large populations. Methods for measurement of nutrient and energy intake leave much to be desired. Questionnaires and diaries of food intake are plagued by underreporting. Precise methods for estimating energy intake, as would be required to define differences in intake responsible for weight gain, are not available. The most objective and accurate method for assessing the level of physical activity and energy expenditure of activity is average-daily metabolic rate, determined by the doubly labeled water, minus the basal metabolic rate. This method, however, is limited to studies in small numbers of subjects. More applicable to population studies are motion sensors, specifically, accelerometers. These instruments reliably assess patterns of physical activity. Accelerometers offer the advantage of measuring motion from nonexercise (i.e., lifestyle) activity as well as exercise activity. Another way to estimate "integrated" physical activity is to measure cardiorespiratory fitness. This measure is represented by maximal oxygen consumption determined under exercise conditions. This measurement carries the advantage of being quantitative and available for epidemiological studies. It is not, however, a direct measure of physical activity but only a reflection of it. Moreover, cardiorespiratory fitness is largely an indication of recent intensive exercise; it may not be a useful tool to assess the effects of moderate exercise, and it is also influenced by inherited characteristics. PHYSICAL ACTIVITY IN THE ETIOLOGY AND TREATMENT OF OBESITY Sedentary life habits and inactivity in the etiology of overweight and obesity. No RCT are available that address whether sedentary life habits and inactivity contribute to the development of obesity in populations. Available data therefore are restricted to observational studies (Evidence Category C). Studies of ecological trends in populations provide suggestive evidence that declining amounts of physical activity have contributed importantly to a rising prevalence of overweight and obesity. Some studies have reported secular decreases in energy intake concurrently with increases in body weight, both in children and adults; these decreases infer a corresponding even greater decrease in energy expenditure, which would be a requirement for weight gain. Two cross-sectional studies, each on about 700 children, noted lower levels of activity being correlated with higher levels of body fatness. In these studies, confounding variables could not be fully excluded. Children of parents with less formal education and lesser incomes had greater body fatness that was associated with more watching of television and other sedentary activities. In another cross-sectional study, Minnesota researchers used questionnaires to obtain information about food intake and exercise frequency on large samples of women and men. Body weight correlated inversely with high-intensity exercise in men and with both high-intensity exercise and walking in women. At the same time, high consumption of certain foods and drinks—alcohol, dairy products, and meat—were positively associated with body weight. This study supported a dual etiology for increased body weight. A review of eight prospective studies revealed some link between low levels of physical activity and risk of developing obesity. In one study in United States male health professionals, those reporting vigorous exercise had lower body weights at follow-up. There was a direct association between television viewing habits and body weight. Relationships were more pronounced in middle-aged men than elderly men. In the Women's Gothenburg Study, low levels of leisure-time physical activity appeared to be a risk factor for weight gain in women consuming high-fat diets. Taken together, the various observational studies support an inverse relationship between the level of physical activity and body fatness. This support resides in Evidence Category C, and it can be called only moderately strong—the data suffer from a lack of precision in measurements of energy intake and total physical activity. Prevention of weight gain through physical activity. RCT are not available to address whether physical activity can prevent weight gain in the general population. Data are restricted to observational studies (Evidence Category C). The age-related pattern of body weight demonstrates an increasing prevalence of weight gain through the sixth decade. Several large-scale longitudinal studies have assessed the role of habitual physical activity in preventing the progression of weight gain from acceptable weight through overweight to obesity, along with its attendant comorbidities. These studies suggest that physical activity and fitness attenuate weight gain but do not necessarily prevent weight gain or promote weight loss. Fitness (and maintaining fitness) further appears to protect against sizable weight gain. Although body weight increases with advancing age, even among the most fit and highly active, this increase may be attenuated through physical activity. Avoiding a sizable weight gain with aging through physical activity nevertheless may mitigate comorbidities of obesity. A considerable body of data exists that physical activity can attenuate weight gain with aging with attendant benefits in reduction of comorbidities (Evidence Category C). Treatment of overweight and obesity in adults. Ten RCT have addressed whether exercise interventions alone will produce weight loss. The majority of these studies show that physical activity alone in the form of aerobic exercise produces some weight loss. The effect of exercise alone on weight loss nonetheless appears to be modest—generally about 1–2 kg over the duration of study. Evidence from this group of RCT was not considered robust enough for Evidence Category A. Several studies were relatively small, and on the whole, observed weight changes were modest, although consistent. The panel therefore assigned the summed results to Evidence Category B. Another 13 RCT examined whether the combination of reduced-energy diets and increased physical activity produce a greater weight loss than does a low-energy diet alone. Most studies favored diet + exercise regimens over diet alone, but the difference was statistically significant in only a minority of studies. In one of the latter, diet + exercise proved better in men but not in women. The panel concluded that the overall lack of statistical significance was probably due to the short time-frame of the exercise programs, small sample sizes with inadequate statistical power, and difficulty with to These in placed the summed results of this group of RCT in Evidence Category B. A of the prior RCT were to examine whether a of diet + exercise produces better maintenance of weight loss than does diet alone. data from RCT in adults are limited by small sample sizes and by long-term to the exercise and diets. RCT that on the significant long-term effects diet + exercise over diet the were The relatively trends of the studies the panel to that diet + exercise provides over diet alone in maintaining weight loss (Evidence Category This is by as well as studies of weight which show that physical activity is associated with better long-term maintenance of weight loss (Evidence Category C). Treatment of obesity in children and Obesity in appears to be of prevention of obesity in and is RCT have whether low energy diets + exercise produce better weight loss than diet alone in The RCT were relatively small and were not to provide a Taken together, the RCT that exercise to low-energy diets for changes in overweight or body fat (Evidence Category The evidence further to the panel that whereas exercise in overweight children and has limited effects on overweight it still body The fitness risk (Evidence Category Physical activity for prevention and treatment of weight gain in RCT were not that whether increased physical activity or weight gain during observational studies of exercise in have examined weight gain as an prospective study women to active during their with women to their exercise the women of weight gain and significantly increases in fat by the of with women. according to an observational study, women had lower levels of leisure-time physical activity more of their weight gain than those These observational studies were considered to be suggestive of of exercise for weight both during and and were assigned an Evidence Category The panel concluded that the development of physical activity interventions in women a for the prevention of overweight and obesity in women (Evidence Category Physical activity and changes in body weight and fat distribution at gain during and after to overweight and obesity in women. RCT have an exercise to no and another RCT have diet + exercise to diet alone on body weight and fat distribution in women. The results of these RCT do not a as to whether physical activity will prevent or a gain in total body fat or abdominal fat after the or whether exercise provides over diet alone in an obesity treatment for women. The available RCT were to be to address this On the other hand, observational studies, both cross-sectional and suggest that women with high levels of physical activity have lower body fat and less abdominal fat during the than do those with low levels of physical are less to gain in total body fat and abdominal fat (Evidence Category C). populations. Several studies have examined whether exercise in the population can of muscle and of fat that with advancing The panel considered studies of at least duration and that exercise but not in from to and or aerobic in about of studies with aerobic and in about half with fat mass the of loss of fat mass on duration of the fat mass and increased mass, to the duration of the exercise The panel concluded that fat mass and increases muscle mass in over whereas aerobic fat mass but does not increase muscle mass (Evidence Category Physical activity and abdominal obesity. RCT examined whether increased physical activity alone, weight will reduce body weight and abdominal In of of exercise to reduce body weight, body fat, or abdominal obesity. In only one RCT exercise alone produce significant weight loss and decrease in abdominal In the same exercise alone or no in body weight, body fat, or abdominal these studies were not to whether there was a reduction in abdominal and abdominal fat are exercise has been in one randomized and trials to in in both The panel concluded that increased physical activity alone weight loss is not associated with in abdominal Physical activity with or weight loss is associated with in and abdominal (Evidence Category C). AND studies show the relationship between BMI and total to be with occurring in the BMI of along with and the increased at the in the 5 and by the to the studies a relationship with increasing progressively from to highest levels of and may the relationship between physical activity and in (Evidence Category C). This category of evidence is by a study in in which leisure-time activity correlated positively with lower after for and factors. These various studies still may not for life risk and all of which are correlated with BMI and of and life have changed over have been to environmental that further the of These confounding however, do not the relationship between BMI and which is and (Evidence Category C). comorbidities. epidemiological and metabolic data that obesity to a number of medical disease, and certain of This which to Category C but is has been in in the recent OEI report The of obesity to heart disease, heart and to be independent of the of obesity on risk factors. epidemiological and metabolic studies an of obesity on risk to and upon the development of This is the body fat is to the and (Evidence Category C). In spite of the associations between obesity and its much to be about and quantitative of these and and RCT show that increased physical activity and in obese (Evidence Category data suggest that exercise alone and exercise with weight reduction the from to (Evidence Category C). treatment of in with diabetes, studies on the of exercise are Although exercise with engage in high-intensity Further, in are the treatment of toward more to any benefits from exercise are short exercise is to be an in the long-term of it must be regular and studies that the obesity is increased small and low it in overweight appears to be more to high of and and than to overweight per observational studies, RCT of months duration and of large enough sample to significant changes in (and other have been These studies that in the absence of weight loss at least an increased physical activity or in overweight women or or men. physical activity is of a that results in at least weight will be and in men and women. Further, the of physical activity to a diet will the effect of the diet in overweight men and women. in men and women with the of physical activity to a weight diet significantly the effect of the The panel considered the RCT evidence for these to be (Evidence Category A review of study and revealed that aerobic by after for weight loss and and after for the number of in each Blood was significantly more in of than in study in were independent of weight loss and were not to body mass eight RCT that exercise alone is less for reducing than diet alone moreover, exercise to a low-energy diet does not reduce significantly more than does diet alone. The panel concluded that RCT provide evidence that physical activity can reduce in both lean and obese subjects. reduction is independent of weight loss or changes in body composition, although the response does not go the reduction by diet alone (Evidence Category Cross-sectional surveys further suggest an inverse relationship between habitual physical activity or physical fitness and prospective studies that active have both lower and a of these effects appears to be independent of a number of confounding BMI or body In one study, not engage in vigorous play at in a greater risk for developing than those this difference was observed only in those were overweight at The panel that observational studies support the that physical activity the risk for developing independent on its effects on body or body (Evidence Category C). A state is one of the metabolic that has been reported to in obese The effects of physical activity on the are and not well Physical activity has an effect of and This effect might the that during data further suggest an effect of physical activity on over a cross-sectional studies suggest an inverse relationship between levels of physical activity and RCT and studies whether the is or other factors. Taken as a whole, observational studies are suggestive that regular physical activity is (Evidence Category C). RCT data further suggest that physical activity on a regular (Evidence Category observational studies have found an association between obesity and some of of the and the obesity a role in the development of these is studies also a inverse relationship between physical activity and The and of this association is that a (Evidence Category C). studies of physical activity and in overweight or obese Among over 700 to this were as data on the of physical activity to and in of overweight and obese addressed was whether higher levels of physical activity or fitness reduce and in overweight or obese The panel that active and fit to have lower of disease and than are not This was in various of body A was whether overweight and obese are active have a lower risk of and than normal weight are The data that being active and fit and decreases risk for and that active and fit are overweight or obese have lower and risk than normal weight are The evidence to these was considered to be moderately and was under Evidence Category The prevalence of overweight and obesity is high and is increasing in the United States and other nations These a of and as well as and obesity are due to a relatively high intake of energy that is not with energy expenditure. of energy expenditure from exercise and other of physical activity. most in our sedentary is to the and is a supported by observational studies. On the other hand, the to the of overweight and obesity from the of regimens of moderate exercise in the general population. in energy expenditure about by moderate exercise are to weight gain with advancing or to higher levels of overweight and obesity. Further, current are not to in energy expenditure through increased physical activity. of energy intake and to increase physical activity will both be to with the "epidemic" of overweight and obesity. a large body of evidence has been to support the to increased physical activity in a of weight Some of this evidence from although there have been too studies in the exercise observational studies, however, support to a for regular physical activity in weight suggest that a in physical activities in both and leisure-time to increasing overweight and obesity, and a of to and physical activity would to current Several RCT further that a physical activity with low-energy diets weight loss and maintenance of lower body increased physical activity appears to have an independent effect on comorbidities of obesity, a In an active and fit way of life appears to attenuate and risk in overweight and obese of patterns and trends in physical activity is needed for samples of the population. methods of measurement for observational studies are also evidence-based recommendations RCT to the results of observational studies. epidemiological and new and These can be by of human and in some and clinical of can be only through The of physical activity and exercise physiology are rich in observational studies and in human and On the other hand, it is in although in recent an number of RCT are being It nonetheless can be that one of the in the field of physical activity is for more and RCT of physical activity in overweight and obese groups. If results of RCT on the benefits of physical activity are to be to the medical must be based on must have a sample and statistical to a The of exercise in the of the study must be high enough to significantly and to the exercise must be The of the study be defined and be in quantitative Among effects of on of weight loss maintenance of weight loss be The both men and previous trials to have been in women subjects. RCT be to both and on to of the Development of is for might be to or of physical activity, than a of exercise sedentary groups. If RCT to the impact of physical activity on body weight are to be quantitative will be A is for the to measure physical activity. is although is The use of as a for physical activity more of physical fitness may be an independent to health The field of physical activity with the field the for accurate measurements of energy consumption. The doubly labeled is the for estimating energy (and intake in a but is for use in epidemiological studies. quantitative is RCT are to their in the for quantitative measurement is a in will a more accurate of the benefits of physical activity in the treatment of obesity and its comorbidities.