Obesity in adults: Role of physical activity and exercise

INTRODUCTION — A large body of observational data show an association between higher levels of physical activity and lower rates of many chronic diseases [1-5]. Conversely, physical inactivity is a component of reduced life expectancy [4,6]. The energy expended by physical activity is a component of energy balance that is particularly important in the pathogenesis of obesity and in its treatment. The components of energy expenditure are resting metabolic rate (RMR), the thermic effect of feeding (TEF), and physical activity (figure 1) [7].

The management of overweight and obesity includes a combination of dietary changes, increased physical activity, and behavior modification [8]. Some patients may eventually require pharmacologic therapy or bariatric surgery to augment weight loss and weight loss maintenance. Physical exercise and activity are also important for maintaining long-term weight loss and are key in preserving lean body mass during and after weight loss. In overweight adult females, a dose-response relationship has been demonstrated between the amount of exercise and total weight lost as well as long-term weight loss maintenance [9].

The role of physical activity in the prevention and treatment of obesity will be reviewed here. Additional discussion of basal metabolic activities and thermogenesis, as well as other interventions in the management of obesity in adults, are reviewed separately:

●(See "Obesity: Genetic contribution and pathophysiology".)

●(See "Obesity in adults: Etiologies and risk factors".)

●(See "Obesity in adults: Overview of management".)

●(See "Obesity in adults: Dietary therapy".)

●(See "Obesity in adults: Behavioral therapy".)

In addition, obesity in children and adolescents is reviewed separately:

●(See "Definition, epidemiology, and etiology of obesity in children and adolescents".)

●(See "Prevention and management of childhood obesity in the primary care setting".)

●(See "Clinical evaluation of the child or adolescent with obesity".)

OVERALL HEALTH — Physical activity improves physical and mental health in a wide range of domains [5,10]. Conversely, a sedentary lifestyle in adults has been associated with increased mortality [4,11]. In a prospective study of 17,013 Canadian adults, there was a progressively higher risk of all-cause and cardiovascular mortality across higher levels of sitting time [12,13]. The benefits and risks of exercise, independent of its effects on weight, are reviewed in more detail elsewhere. (See "The benefits and risks of aerobic exercise".)

EXERCISE AS PREVENTION OF OVERWEIGHT/OBESITY — Exercise is important for the primary prevention of obesity [14]. Low levels of physical activity and recreation are related to weight gain [15]. Maintaining adequate physical activity reduces the risk of weight gain [16-18] and the risk of cardiovascular disease [12,13]. As an example, in young adults transitioning to middle age, higher compared with lower levels of physical activity over 20 years were associated with smaller gains in weight [16]. In this young (mean age 25 years), normal-weight population, 150 minutes of moderate activity per week was adequate to prevent weight gain.

In older or obese adults, however, higher activity levels may be necessary for prevention of weight gain. In a cohort of over 34,000 females (mean age 54.2 years) who were consuming a usual diet and were followed for a mean of 13 years, there was a mean weight gain of 2.6 kg [19]. Compared with females who engaged in >420 min/week of exercise, females who engaged in <150 and 150 to <420 min/week gained significantly more weight (0.12 and 0.11 kg, respectively). Physical activity was inversely related to weight gain only among normal-weight (body mass index [BMI] <25 kg/m²) females. Thus, in order to maintain normal body weight in the midlife, higher levels of physical activity (approximately 60 minutes/day) were necessary. Once overweight, physical activity in the absence of controlling caloric intake did not prevent weight gain. (See 'Exercise is modestly beneficial for weight loss' below.)

In a 12-month, randomized trial, adults (mean age 55 years, mean BMI 29 kg/m²) who were randomly assigned to a moderate to vigorous exercise intervention (60-minute session six days/week) were better able to maintain their weight than controls (-1.4 versus +0.7 kg for females, -1.8 versus -0.1 kg for males) [20]. Exercisers also had significant decreases in waist and hip circumferences, fat mass, and percentage body fat. After 12 months, those in the intervention group were exercising a mean of 298 min/week compared with 68 min/week in the control group. These results suggest that in older individuals (particularly females), more than 68 min per week and perhaps at least 300 min of exercise/week may be necessary to prevent long-term weight gain.

The contribution of physical activity interacts with genetic factors in the prevention of obesity. A meta-analysis of 45 studies in adults evaluating the interaction between physical activity and genetic risk for obesity showed that the risk of obesity in patients with FTO variants (associated with higher BMI and waist circumference) was attenuated by physical activity [21]. These findings suggest that physical activity is likely to protect against obesity regardless of an individual's genetic predisposition to it.

TREATMENT FOR OBESITY — Exercise has been evaluated as a single treatment for obesity, in combination with diet, and for maintaining weight loss after successful completion of a weight-loss program. In most studies, exercise only modestly improves weight loss [22-24]. The reasons for this finding are uncertain but may be due, in part, to difficulty in adhering to sufficiently vigorous exercise regimens. In addition, for patients who are adherent with exercise training, increases in muscle mass, plasma volume, and glycogen stores may offset loss of adipose tissue, resulting in less net weight loss.

Exercise is modestly beneficial for weight loss — Several studies have evaluated the effect of exercise alone in inducing weight loss [22]. In meta-analyses of trials (duration 12 weeks to 12 months) examining the effects of exercise on weight loss, exercise resulted in modest reductions in weight compared with no treatment (weighted mean difference -1.6 kg) across all studies, which was comparable when comparing high- versus low-intensity exercise (mean difference -1.5 kg) [23,24]. In addition, exercise modestly decreased waist circumference and blood pressure.

While it may be difficult to lose weight with exercise alone, exercise appears to have a beneficial effect on reducing body fat. In a 12-week study on change in body composition and insulin resistance in 52 males who lost an average of 7.5 kg with either diet- or exercise-induced weight loss, the main findings were as follows [25]:

●A greater reduction in total body fat in the exercise-induced weight loss group

●Similar reductions in abdominal obesity, visceral fat, and insulin resistance in the two treatment groups

●In a third treatment group assigned to exercise without weight loss (increased caloric intake to match energy expenditure), abdominal and visceral fat was decreased but to a lesser degree than in the other treatment groups

Exercise also has beneficial effects on body composition in premenopausal and postmenopausal females [26,27]. In a randomized, 12-month trial in postmenopausal females evaluating moderate-intensity exercise (most commonly brisk walking for an average of three hours per week) versus a control group with only a stretching program, the exercise group lost more weight (mean difference -1.4 kg) and had greater decreases in body fat, intraabdominal fat, and subcutaneous fat [26].

Adding exercise to diet is only minimally beneficial for weight loss — Exercise programs added to diets with moderate to severe caloric restriction have little additional effect upon weight loss. As an example, a systematic review of 17 randomized trials including overweight people and those with obesity (body mass index [BMI] 25 to 37 kg/m²) showed that, compared with weight loss by diet alone, adding exercise to diet produced slightly greater weight loss than diet alone (mean increase in weight loss approximately 1.5 kg) [28]. However, the results achieved statistical significance in only two of the trials. The exercise interventions ranged from 60 to 240 min/week. Similar findings were subsequently reported in older adults with obesity (mean age 70 years) who were randomly assigned to diet or exercise alone, diet plus exercise, or control [29]. Body weight decreased similarly in the diet alone and the diet plus exercise groups (10 and 9 percent, respectively) but did not decrease in the exercise alone or control groups. However, physical functioning improved significantly in all treatment groups compared with controls, and the improvement was greatest in the combined diet plus exercise group (increase from baseline of 21 versus 12 and 15 percent for diet and exercise alone, respectively).

The frequency and intensity of exercise may explain why exercise does not improve weight loss above that achieved with calorie restriction. If a patient utilizes 100 calories during exercise each day (700 calories per week), it would take roughly five weeks to utilize the energy (3500 calories) in one pound of fat. Thus, it takes a considerable amount of time and effort to expend calories via physical activity that results in noticeable weight loss. In trials that were designed to assess higher intensity or longer duration of exercise (up to 300 min/week), the following findings were reported:

●In a 12-month trial of 184 overweight, sedentary females (mean BMI 32.6 kg/m²) who were randomly assigned to one of four exercise programs (ie, low intensity/low duration, high intensity/low duration, low intensity/high duration, high intensity/high duration), in addition to caloric restriction, weight loss was the same in all groups, regardless of exercise intensity or duration [30]. The mean achieved duration of exercise in the highest-duration groups was approximately 200 min/week.

●In a 12-month trial of 130 adults with severe obesity (mean BMI 43.6 kg/m²) who were randomly assigned to immediate or delayed physical activity in addition to caloric restriction, the initial activity group lost significantly more weight in the first six months than the delayed-activity group (10.9 versus 8.2 kg) [31]. After 12 months, at which time both groups were participating in an exercise program, the magnitude of weight loss did not significantly differ between the two groups (12.1 versus 9.9 kg). However, the addition of physical activity resulted in greater reductions in waist circumference and hepatic fat content. This trial was limited by high attrition rates (20 to 25 percent) and difficulty in achieving the desired exercise duration (300 min/week). Rather, the mean achieved duration of vigorous physical activity was only 71 min/week.

Adding exercise to a calorie-restricted diet may have important physiologic benefits independent of weight loss, however. As a result of any weight loss, approximately 20 percent is due to loss of lean body mass (eg, muscle mass), with the remaining 80 percent due to loss of fat. Increased physical activity attenuates the diet-induced loss of muscle mass [32], which in turn increases physical functioning and insulin sensitivity.

Combined aerobic and resistance exercise is best for weight loss in older adults — Obesity is a particular problem in older adults as it worsens the age-associated decline in function and frailty. While weight loss may improve some health risks, it can also worsen frailty by accelerating the age-related decline in bone and muscle mass [33]. It appears that the addition of exercise to weight-loss programs can help prevent the reduction in muscle and bone mass induced by weight loss, but the type of exercise is important. In one clinical trial of 160 adults with obesity in a six-month weight-loss program, combined aerobic and resistance training improved functional status more than either type of exercise alone [34]. (See "Physical activity and exercise in older adults", section on 'Benefits of physical activity in older adults'.)

No increased weight loss with use of "activity trackers" — Wearable devices that monitor and provide feedback on physical activity and diet do not appear to provide additional benefit over standard behavioral weight loss interventions. In a trial of 470 overweight or obese adults, subjects were randomized to a standard intervention (self-monitoring of diet and exercise) or an enhanced intervention (use of a wearable device with a web interface to monitor diet and physical activity). After 24 months, both groups had similar improvements in body composition, fitness, physical activity, and diet, but the addition of a wearable device resulted in less weight loss than the standard behavioral weight loss program (3.5 versus 5.9 kg) [35].

In a second trial of 800 subjects ages 21 to 65 years, the use of activity trackers for six months (either alone or with incentives [cash or charitable donations]) did not improve health outcomes (weight and blood pressure) when compared with a control group (no tracker or incentives) [36].

Exercise importance in maintenance of weight loss — In observational studies, exercise consistently stands out as an important factor in maintaining weight loss after any weight reduction [9,14,37-40].

●In a meta-analysis of 493 studies (observational studies and randomized trials) involving aerobic exercise for short durations (average 15.6 weeks), diet, or a combination of both in moderately overweight subjects (average BMI 33.4 kg/m² with an average weight of 92.7 kg), the diet-and-exercise group maintained 8.6 kg of weight loss after one year compared with 6.6 kg in the diet-only group [41].

●In a subsequent prospective study including over 4500 premenopausal females, individuals who maintained ≥30 min/day of activity were less likely to regain weight than those who remained sedentary (odds ratio [OR] 0.7, 95% CI 0.5-0.9) [39].

By contrast, results from randomized trials are mixed, with many showing no significant difference in weight regain for diet only versus diet plus exercise [28]. The reason for this is unclear since observational studies repeatedly suggest an essential role for physical activity in weight loss maintenance [42]. In many trials, participants had difficulty adhering to the exercise regimens, a limitation that may explain, in part, the difference in the findings. Other limitations include variability in the amount and duration of exercise prescribed. In one systematic review of observational and randomized trial data, weight regain was reduced by participation in high levels of physical activity (eg, at least 60 min/day brisk walking), a level not achieved by most patients [14]. Post hoc analysis of a randomized trial shows a clear dose-response relationship between physical activity and weight-loss maintenance [30].

The addition of exercise to pharmacotherapy may have additional efficacy for weight loss maintenance. In a randomized controlled trial including 195 individuals with obesity initially treated with an eight-week low-calorie diet, all participants were randomly assigned to one year of moderate to vigorous exercise, liraglutide (3 mg/day by subcutaneous injection), combination exercise-liraglutide therapy, or placebo [43]. After an average 13.1 kg initial weight loss, those in all treatment groups maintained weight loss compared with placebo: exercise alone (-4.1 kg), liraglutide alone (-6.8 kg), and combination exercise-liraglutide therapy (-9.5 kg). Compared with liraglutide alone, combination exercise-liraglutide resulted in greater weight loss, although the results did not achieve significance (-2.7 kg, 95% CI -6.3 to 0.8 kg).

PHYSICAL ACTIVITY PROGRAM

Determine the most appropriate exercise program — Any exercise program should be designed to fit into the health and physical conditions of the participant. Persons who are about to begin an exercise program, even those whose only exercise will be walking, should be advised of the possibility of musculoskeletal stresses and strains and joint injury. Existing medical conditions, age, and preferences for types of exercise should all be considered in the decisions. Medical evaluation prior to initiation of an exercise program is typically not necessary for asymptomatic patients at low risk for coronary heart disease. However, there may be certain groups in which evaluation is warranted. This topic is reviewed in detail elsewhere. (See "Exercise for adults: Terminology, patient assessment, and medical clearance", section on 'Medical assessment and clearance for exercise'.)

Goal exercise type, intensity, and duration — There are numerous health benefits of physical activity, and individuals performing the least physical activity benefit most by even modest increases in moderate to vigorous physical activity [5]. Additional benefits occur with more physical activity; both aerobic and muscle-strengthening physical activity are beneficial.

For weight loss, the goal is to increase energy expenditure by 1000 to 1200 calories per week, or slightly more than 150 calories per day. An objective measurement of energy expenditure should be used since people overestimate their energy expenditure from activity by more than 50 percent [44]. The amount of energy expended depends upon the duration and intensity of the exercise and the subject's initial weight. As an example, a 120-pound person walking three miles per hour expends slightly less than 2 calories per minute more than standing still. At 160 pounds, the difference is 2.4 calories per minute, and at 200 pounds, it is 3 calories per minute. Thus, a 30-minute walk at three miles per hour for a person weighing 200 pounds would dissipate an extra 90 calories as compared with 60 calories for a person weighing 120 pounds.

In the weight loss maintenance period, most people require >60 minutes per day of moderate-intensity activity to successfully maintain the loss [14].

The optimal combination of aerobic and resistance exercise is uncertain. In a meta-analysis of trials of progressive resistance strength training in adults, resistance strength training improved physical functioning in older adults [45]. In a subsequent trial, 136 people with obesity were randomly assigned to one of four groups (resistance, aerobic, combined, or sedentary control) [46]. After six months, body weight decreased by 0.64, 2.77, and 2.3 kg, respectively, and increased by 0.28 kg in the control group. Compared with the control group, cardiorespiratory fitness increased in the aerobic and combined-exercise groups. Abdominal and visceral fat decreased and endurance increased in the aerobic and combined groups, whereas skeletal mass and muscle strength increased in the resistance and combined-exercise groups. Insulin sensitivity improved in the aerobic and combined groups. Thus, combined aerobic and resistance training is optimal.

In another trial assessing intensity of exercise in 300 adults with central obesity, there were similar reductions in weight (5 to 6 percent decrease) and in waist circumference (-4.6 cm) with high- and low-intensity exercise, given fixed amounts of energy expenditure [47]. However, compared with control, only the high-intensity group showed significant reductions in two-hour oral glucose tolerance test (OGTT; 75 g glucose load).

For many people, walking may be the most appropriate form of exercise. In one study of females with obesity, the combination of diet plus advice to increase physical activity by incorporating short periods of activity into daily schedules (eg, walking instead of driving short distances, taking stairs instead of elevators) was as effective for inducing weight loss as diet plus structured aerobic activity (aerobics classes) [48].

Health benefits associated with exercise — Exercise and physical activity have several health benefits, even in the absence of significant weight loss (table 1) (see "The benefits and risks of aerobic exercise" and "Exercise and fitness in the prevention of atherosclerotic cardiovascular disease"):

●Exercise can improve glycemic control and insulin sensitivity and may prevent the development of type 2 diabetes. It appears, however, that both aerobic and resistance training must be part of the exercise regimen [49]. (See "Exercise guidance in adults with diabetes mellitus".)

●Among people with obesity, those participating in both aerobic and resistance training demonstrated greater improvement on an evaluation of global functional status compared with those participating in either aerobic or resistance training alone (21 percent versus 14 percent) [34].

●Aerobic training has beneficial effects on serum lipoprotein concentrations, body composition, and aerobic capacity and improves hemostatic factors associated with thrombosis. (See "Effects of exercise on lipoproteins and hemostatic factors".)

●Long-term aerobic exercise regimens have, in most studies, had a beneficial effect upon the systemic blood pressure. (See "Exercise in the treatment and prevention of hypertension".)

●Long-term exercise programs cause a greater decrease in abdominal fat than lower body fat and help maintain it [50]. This is important because people with abdominal obesity are at increased cardiovascular risk. (See "Obesity in adults: Prevalence, screening, and evaluation".)

●Several studies have found a strong inverse relationship between habitual exercise and fitness and the risk of coronary disease and death [51-53] (see "Exercise and fitness in the prevention of atherosclerotic cardiovascular disease"). The value of exercise for reducing cardiovascular risk can be illustrated by the findings from a meta-analysis of 33 cohort studies evaluating the association between cardiorespiratory fitness and all-cause mortality or coronary heart disease [52]. Compared with patients with a high or an intermediate level of cardiorespiratory fitness, those with a low level had a higher risk for all-cause mortality (relative risk [RR] 1.7, 95% CI 1.5-1.9, low versus high) and for coronary heart disease events (RR 1.6, 95% CI 1.4-1.8, low versus high).

Similarly, in a systematic review of 36 studies, the risk for all-cause and cardiovascular mortality was higher in individuals with normal body mass index (BMI) and poor fitness than in those with high BMI and good aerobic fitness, even after adjustment for other cardiovascular risk factors [53].

Thus, adiposity and fitness level are both important prognostic factors in people with obesity. In the Lipid Research Clinics and the Nurses' Health Studies, both physical inactivity and adiposity were independent predictors of mortality; higher levels of fitness did not completely negate the association between adiposity and mortality [54-56].

Health risks associated with exercise — Exercise has been associated with an increased risk of musculoskeletal injuries, cardiac arrhythmia, acute myocardial infarction, and bronchospasm. (See "The benefits and risks of aerobic exercise".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Obesity in adults".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Exercise and movement (The Basics)")

●Beyond the Basics topics (see "Patient education: Losing weight (Beyond the Basics)" and "Patient education: Exercise (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●The management of overweight and obesity should include a combination of diet, exercise, and behavioral modification. (See 'Introduction' above.)

●Physical inactivity is related to weight gain and increased risk of cardiovascular disease. Increasing the level of physical activity would be beneficial to all ages and all groups, particularly for the prevention of obesity. (See 'Exercise as prevention of overweight/obesity' above.)

●In moderately overweight adults, exercise programs added to diets with moderate to severe caloric restriction have only a modest effect upon weight loss. However, adding exercise to caloric restriction may have other important benefits independent of weight loss. Physical activity attenuates the diet-induced loss of muscle mass, improves physical functioning, and may offset the decrease in total energy expenditure that occurs with weight loss, such that the calorie restriction required to match energy expenditure is more easily achieved. (See 'Adding exercise to diet is only minimally beneficial for weight loss' above.)

●In older adults with obesity, the combination of aerobic plus resistance exercise improves functional status more than either type of exercise alone. (See 'Combined aerobic and resistance exercise is best for weight loss in older adults' above.)

●Physical exercise and activity are important for preventing weight regain after successful weight loss. (See 'Exercise importance in maintenance of weight loss' above.)

●There appears to be a dose effect for physical activity and weight loss, and much greater amounts of exercise are necessary to produce significant weight loss in the absence of a calorically restricted diet. Therefore, when weight loss is the desired goal, a diet should be combined with physical activity and the activity gradually increased over time as tolerated by the patient. For many individuals, >60 minutes per day of activity may be required to prevent weight regain following a significant weight loss. (See 'Physical activity program' above.)

A multicomponent program that includes aerobic and resistance training is preferred. However, any exercise program should be designed to fit into the health and physical conditions of the individual. Existing medical conditions, age, and preferences for types of exercise should all be considered in the decisions. (See 'Physical activity program' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges George Bray, MD, who contributed to an earlier version of this topic review.