Exercise in treating obesity in children and adolescents : Medicine & Science in Sports & Exercise (original) (raw)
Obesity is due to a positive energy imbalance in which energy intake exceeds energy expenditure. Treatments for obesity involve creating negative energy balance resulting in weight loss, and then keeping energy balance stable to maintain normal body weight. Exercise is generally considered one of the cornerstones of pediatric obesity treatment, along with dietary change and behavior modification.
There have been several reviews of the effects of exercise on changes in body weight and body fat (17,37) in adults, as well as exercise in the treatment of adult (17) and child and adolescent obesity (12). These reviews suggest that exercise is useful for weight control. The goal of this manuscript is the review of controlled clinical research using exercise programs in the treatment of pediatric obesity. This includes studies that use exercise alone as well as studies that use both diet and exercise. The studies will be put in the context of other research on exercise for obese children and adolescents, with potential factors mediating the effects of exercise in obese children and adolescents discussed. The review ends with a brief discussion of the possibilities for extending exercise research from treatment to prevention.
METHODS
Articles in which obese children and adolescents were placed on exercise programs for the purpose of weight loss were identified using computerized literature searches (Medline, Psychological Abstracts) and cross-reference of experimental and review articles. Studies included for review met two criteria: 1) children or adolescents were defined as obese using objective criteria for obesity, and 2) obese children or adolescents were provided either different types of exercise programs or an exercise program compared with a no-exercise control condition. Thirteen studies met these criteria and are presented in Table 1. The information presented in this table includes authors, age and number of subjects, study design, characteristics of the exercise and/or diet, length of treatment and follow-up, and significant between group differences for body composition and fitness measures.
Methodological Characteristics of the studies
Experimental design. Random assignment or stratified random assignment was used in 8 of the 13 studies(3,15,18-21,28,39). Three studies matched subjects to groups based on age(35), weight (6), and age, weight, height, and percent overweight (38). In two studies, the method of assignment to groups was unspecified(36,47).
Two studies compared an exercise group and a control group, without a diet(6,47). Five of the studies contrasted a diet and exercise group with a diet only group(21,28,36,38). One of these studies used a factorial design that contrasted fiber content of the diet in addition to exercise (35). Three studies contrasted diet, diet plus exercise, and no-treatment control groups(3,19,39). Finally, three studies investigated ways to structure exercise programs(15,18,20).
Sample characteristics. Studies used a broad range of subject ages, including “prepubertal” subjects (28), subjects 8-12 yr of age(3,6,15,18-21,38), adolescents (35,36,39), and preadolescent and adolescent children (47). Twelve studies included both males and females(3,15,18-20,28,35,36,38,47), with one study using only male subjects (6).
A variety of definitions of obesity were used. These included at least 20% above ideal weight for height(15,18-21,38); two standard deviations above weight for height standards (6); a body mass index (BMI = kg·m-2) greater than 25 and body weight that exceeded the 95th percentile for age (28); skinfold measures (47); and the combination of elevated weight for height and skinfold measures (3,39).
Characteristics of treatment. Eight studies required subjects to exercise at one prescribed level. These programs varied from exercise three to four times per week (3,21,28,39), daily exercise (36,38), exercise five times per week(35), and choice of activity to expend up to 2,800 kcal·wk-1(19). The school-based studies provided two (6) and three (47) extra physical education classes per week emphasizing intensive exercise. The remaining studies (15,18,20) investigated the effects of various types of exercise programs in obese children, including aerobic versus lifestyle programs (18,20) and targeting reductions in sedentary behaviors (15). Ten of the exercise intervention studies also included diet manipulations(3,15,18-21,35,36,38,39). Hills and Parker (28) provided unspecified nutrition education and Blomquist et al. (6) did not manipulate diet.
RESULTS
The results will be discussed in relation to the type of experimental design.
Exercise versus no exercise controls. The two studies that compared exercise versus no exercise controls were school-based. Neither of these studies showed significant effects of exercise on weight variables or fitness (6,47).
Diet versus diet and exercise. The five studies that contrasted diet versus diet and exercise varied with respect to diet and exercise methods, but all demonstrated better changes in weight and fitness for diet plus exercise groups than diet alone. Reybrouck et al.(38) found that after 4 months a group expending 250 kcal in one session of exercise per day, in addition to a low-calorie diet, showed a greater decrease in percent overweight than the diet alone group. In another 4-month study, Hills and Parker (28) found that children who received nutritional information and aerobic exercise three to four times per week had lower summed skinfold measures than the group that only received nutritional information. In a much shorter treatment period of 15 d, Pena et al. (36) demonstrated greater changes in percent body fat for diet plus exercise than diet alone. Epstein et al.(21) provided a 2-month aerobic exercise intervention three times per week in addition to diet. At the 12-month follow-up, greater differences in percent overweight and physical work capacity were observed for children in the diet plus exercise group versus diet alone group. Finally, Pena et al. (35) provided a 1-month treatment, which crossed an isocaloric high- and low-fiber diet with a no-exercise group and exercise group that jogged and cycled twice daily, five times per week. The treatment had different effects. Girls in the high-fiber/exercise group or low-fiber exercise group showed greater decreases in weight than the low-fiber/no-exercise group. In addition, girls in the high-fiber/exercise group showed greater decreases in weight as compared with the high-fiber/no-exercise group. In boys, the high-fiber/exercise group had greater decreases in weight when compared with the low-fiber/no-exercise group.
Diet versus diet and exercise versus no intervention. Three studies added a no-treatment control group to the diet versus diet and exercise design, providing a control for nonspecific effects of intervention. In contrast to the previous studies, none of these found differences between the diet and diet plus exercise groups. Rocchibi et al.(39) found that after 5 months engaging in 15-40 min of aerobic exercise three times per week both the diet alone and diet plus exercise groups showed equivalent and greater decreases in weight and percent body fat than the control group. Becque et al. (3) found no changes in obesity measures when comparing among adolescents in a control group, a dietary intervention group, and a diet group with 50 min of aerobic exercise three times per week. However, they did demonstrate a reduction in high-density lipoprotein cholesterol, diastolic blood pressure, and overall coronary heart disease risk factors in adolescents who engaged in the aerobic exercise as compared with adolescents that in the diet or no intervention groups. Finally, Epstein et al. (19) found that children in the diet alone, and diet and lifestyle exercise groups showed similar changes in percent overweight in contrast to the no treatment control at 2- and 6-month intervals. These significant decreases were observed for both treatment groups at 10 yr (16).
Structure of the exercise programs. Two studies manipulated the structure and intensity of the exercise component of treatment by contrasting a lifestyle with an aerobic (programmed) exercise regime. In both studies the lifestyle and aerobic exercise regimes were isocaloric; however, lifestyle exercise differed from aerobic exercise in many respects. First, it provided the opportunity to include many activities that were not normally considered exercise, such as walking or bicycling to school. Second, it was possible for subjects to break up the caloric expenditure into several small bouts each day, rather than requiring the exercise be done in one bout as in the aerobic exercise program. Finally, the lifestyle exercise program did not require that exercise meet a specific intensity, as was required in the aerobic exercise program. Epstein et al. (18) contrasted aerobic(programmed) and lifestyle activity programs, with or without the Traffic Light Diet. During treatment, all groups showed equivalent decreases in percent overweight and BMI; however, at the 6-month assessment, only the diet/lifestyle exercise and lifestyle exercise-alone groups maintained these decreases. At the 17-month follow-up, both groups incorporating lifestyle exercise continued to have lower percent overweight and BMI than both the diet/aerobic exercise and aerobic exercise alone groups. In addition, while all groups had lower than baseline recovery heart rates at the end of the treatment period, only the diet/lifestyle exercise and lifestyle exercise-alone groups had maintained lower than baseline recovery heart rates at the 6-month assessment. Epstein et al. (20) added a calisthenic exercise group to the design described above and all exercise groups received a diet. The calisthenic group had very low caloric expenditure compared with both the aerobic and lifestyle exercise groups and was included to assess the effects of exposure to a “placebo” exercise program. At the 6- and 12-month assessments, all groups showed equivalent decreases in percent overweight and weight. However, at the 2-yr assessment, the lifestyle exercise group maintained reduction in percent overweight and weight, while the aerobic and calisthenic exercise groups increased in percent overweight and weight. At 5 yr the lifestyle exercise group had lower percent overweight and weight than the calisthenic exercise group, while at 10 yr both lifestyle and aerobic exercise groups had lower percent overweight and weight than the calishtenic exercise group (16).
Epstein et al. (15) evaluated the influence of sedentary behaviors on activity patterns in obese children by contrasting groups that were differentially reinforced for increased physical activity and/or reduction in sedentary behaviors. At the end of the 4-month treatment period, the group that was reinforced for reducing sedentary behaviors had greater changes in percent overweight and percent fat, and showed more of a preference for high intensity activities than the group that was reinforced for increasing physical activity. In addition, the group reinforced for increasing physical activity had greater estimated energy intake than either the group reinforced for reducing sedentary behavior or the group reinforced for both increasing physical activity and reducing sedentary behavior. At the 1-yr assessment, the group reinforced for reduction in sedentary behaviors showed greater changes in percent overweight than either the group reinforced for increasing physical activity or the group reinforced for both increasing physical activity and reducing sedentary behaviors, and they showed greater reductions in percent fat than the group reinforced for increasing physical activity.
DISCUSSION
This review points out the shortage of controlled studies examining the influence of exercise in the treatment of child and adolescent obesity. This situation is not unique to children and adolescents. Pronk and Wing(37) only identified 12 randomized controlled studies evaluating the additive effects of exercise to a diet regimen. Given the small number of controlled studies in children and adolescents, and the mixed outcomes of the studies, there are very limited conclusions that can be made. The two studies that did not involve a diet intervention contrasted exercise and no exercise controls, and found no effects of the exercise intervention(6,47). However, there were consistent findings that exercise plus a diet can increase changes in obesity measures(21,28,35,36,38) and fitness(15,18,21,39), although three studies did not find improvement in weight control when exercise was added to diet(3,19,39). Finally, the three studies that contrasted different types of exercise programs demonstrated that the weight loss effects of activity programs can be enhanced up to 2 yr by using lifestyle versus more programmed aerobic exercise(18,20), but that the two exercise groups were both equally effective in maintenance of weight, and did not differ in contrast to the calisthenics control at 10 yr (16). In addition, reducing access to preferred sedentary behaviors was superior to reinforcing active behavior choices for weight control and fitness improvement at 1 yr(15).
Factors That Can Influence the Effects of Exercise Programs
Exercise adherence. The most important, and neglected, component of exercise intervention research is exercise adherence. A large body of research has focused on the difficulties of exercise adherence in children and adults (10,43). It is impossible to properly evaluate the influence of exercise unless subjects engage in the majority of the exercise sessions for the planned duration and intensity. Negative exercise results in the studies reviewed(3,6,39) may have been due to poor adherence in their exercise programs.
Failure to adhere to the exercise program also limits the long-term effectiveness of the intervention. The development of protocols that maximize short- and long-term adherence was the rationale behind the examination of lifestyle rather than structured aerobic exercise programs(18,20), as well as the examination of the influence of competing sedentary behaviors and active behaviors on pediatric obesity (15).
Attempts to improve adherence were also in part the rationale behind many of the school-based obesity intervention programs(7,8,41). Although the controlled research on school-based exercise programs has not shown unique effects of exercise without diet, Hayashi et al. (27) and Sasaki et al.(44) did show large effects of exercise without diet intervention using intensive school-based aerobic exercise programs consisting of 20 min of running near blood lactate threshold, 7 d·wk-1, for 2 yr. While these studies did not use obese controls, they show the potential of vigorous exercise programs for the treatment of obesity.
Ideas about promoting exercise adherence in obese children and adolescents may be derived from adherence research that does not focus on obesity(10). However, there may be some important differences in obese as compared with nonobese children or adolescents that make it more difficult for them to adhere to exercise programs. Obesity predicts poor adherence (10), and we have demonstrated that environmental contingencies must be stronger in comparison with nonobese children before obese children will choose active behaviors over sedentary ones (13,50). The source of these differences is not known and could include physiological as well as psychological variables.
Finally, adherence research must address the difficulty in measuring exercise behavior. There is a large literature demonstrating the problems of obtaining valid measures of activity, with suggestions on the types of measurements that can be used to enhance confidence in the validity of the assessment of activity in children or adolescents(11,30,42).
Diet. A decrease in caloric intake through manipulation of diet is the most powerful way to lose weight. Diet changes make a bigger impact on negative energy balance than calories expended due to exercise, but the combination of the two can increase negative energy balance and theoretically can improve weight loss over diet alone. The impact of diet as the major component of weight loss may make it difficult to demonstrate diet versus diet plus exercise effects. As caloric reduction increases, and weight loss due to diet is greater, a floor effect on the influence of further decreases in weight due to increasing activity may be observed. This may have been in part the reason for the equivalent decreases in percent overweight for children given diet or diet plus exercise in the Epstein et al.(19) study. To date, there has been no research evaluating differential doses of diet or exercise or the combination of different doses of diet or exercise.
Diet and exercise programs may interact to facilitate or compromise the effects of either. There is basic animal research suggesting that caloric reductions lead to spontaneous increases in activity, though these increases may only be limited to nonobese animals (46). Eating-disorder researchers have conceptualized the increases in activity in anorexia and bulimia patients as being caused in part by the reductions in caloric intake (4). It would be interesting to evaluate interventions that capitalized on any energizing effects on activity due to caloric reduction.
In addition to the degree of caloric reduction, the composition of the diet may be important in influencing effects of exercise intervention. Pena et al.(35) found that for girls, exercise improved the reduction in weight due to either high- or low-fiber diets in comparison to the diet alone, but this effect was not observed for boys. No effects of the high or low fiber diets were observed, and the effects of varying fiber content in the diet on activity patterns were not studied. Another way to study diet composition and its effects on activity would be to manipulate macronutrient content. Theoretically, the thermogenic effects of diets should vary as a function of fat versus carbohydrate content, with high-carbohydrate diets having greater diet-induced thermogenesis and thus producing larger weight loss than high-fat diets (45). This differential weight loss could variably affect activity patterns. In a recent test of this hypothesis, Bandini and colleagues (2) found that macronutrient composition of the diet did not influence diet-induced thermogenesis, but rather influenced total daily energy expenditure by affecting voluntary activity. Diets high in carbohydrates may result in enhanced weight loss relative to high-fat diets in part by energizing activity. It might be very important to assess whether these differences in voluntary activity due to differences in diet macronutrient content could be used to promote increases in activity in obese children or adolescents.
Age. The goal of the treatment for obesity in children or adolescents should be to modify energy balance in a way that best promotes the modification of body composition, while teaching children better eating and exercise habits. The goals for dietary restriction should be tailored to the age of the child. As a general rule, if the child is young, not very obese, and has not reached his/her peak height velocity, then very moderate dietary restriction and an activity program should be sufficient to facilitate the child growing into his/her weight, thus altering body composition. This approach may be most effective for younger children, particularly those between the ages of 2 through about 6. This is a period when child BMI naturally decreases (34,40). It must be kept in mind that obese children and adolescents are overnourished and are generally taller than nonobese children or adolescents of the same age. Therefore, adjustments to population growth curves are needed when estimating the effects of growth on obesity, since obese children may reach their peak height velocity faster than nonobese children (22).
Older children, adolescents, and very obese young children will not benefit as much from growth as moderately obese younger children, and these children and adolescents require greater dietary restriction. The general rule should be to use a diet that provides recommended nutrients and promotes growth while reducing body fat. Research has shown a balanced diet meeting nutrient goals is possible in obese children treated from 8 to 12 yr of age(49), with no decrease in growth over 5- and 10-yr intervals, and no influence on height attained in young adulthood(14). Adolescents will not benefit as much, if at all, as younger children from changes in height in relation to weight.
There may be important developmental reasons for emphasizing one type of exercise over another. The epidemiology of activity suggests that spontaneous activity decreases with age (43). Intervention programs should consider normal changes in activity as children age, as well as take advantage of age-related differences in activity levels and in preferences for different activities. Likewise, the social support systems of children and adolescents are very different and require interventions based on differential social support networks for maximal weight loss results(43). Children of different ages may differ in the activities they can perform, and equally important, like to engage in. For example, resistance training has not been tested in a systematic way in obese children, but may be useful in producing increases in lean body mass and modify body composition (51). However, there are concerns about the safety of resistance training for prepubescent children, and it may be safer and better suited for adolescents (1).
Gender. Finally, only one study reported differential effects of exercise on loss of weight in male and female adolescents(35). Despite this limited database, there are several reasons to assume that gender effects may be important in child or adolescent treatment of obesity. First, gender differentially influences body composition during development, with the effects more marked as the child enters adolescence. One of the more interesting effects has been identified by Mueller (33). During adolescence, a redistribution of fat occurs from the periphery to the trunk in both boys and girls. However, in boys the extremity loss has been reported to be greater than in girls(33). As a result, males are likely to have a more central body fat distribution while females are likely to have a more peripheral fat distribution. In adults, the male-type body fat distribution has been associated with increases in a number of diseases including coronary heart disease (31), diabetes (25), and hypertension (52). This differential distribution of body fat in boys and girls should be considered when assessing the effects of a weight loss program on reduction in body fat.
In girls, the timing of menarche has been found to be associated with higher adiposity levels in early adulthood (24) and in women as old as 80 yr of age (24) with earlier maturation predicting higher adiposity at these ages. Likewise, heavier girls reach menarche earlier than thin girls (23). Based on these relationships one may speculate that there is some common mechanism that affects both the timing of maturation and fatness. Weight loss in girls associated with reduction in body fat may affect menarche onset and this change in hormone cycles could affect how girls respond to dietary restriction and changes in activity level.
In addition to these biological differences, there are different social pressures to be active and athletic in boys and girls(43). Boys and girls are socialized differently regarding exercise, have different exercise skills, and may prefer different types of activities (43). The type and structure of the exercise may need to take child gender into account in program design to obtain optimal results.
Type of exercise. The type of exercise and structure of the exercise program can influence adherence and weight control. The majority of programs focus on aerobic exercise, but lifestyle exercise may be useful in weight control, and other forms of exercise, such as resistance training may play a role. The design of exercise programs in children or adolescents may benefit from new ideas in adult exercise that suggests the importance of shifting people from sedentary to moderate activity, rather than focusing on high-intensity exercise programs (5,26). Lifestyle exercise programs attempt not only to increase caloric expenditure, but also to build activity into a child, adolescent or adult lifestyle. These programs maximize choice and perceived control over exercise behavior, and may increase adherence when compared to more structured aerobic exercise programs.
Interventions in children and adolescents should take advantage of the fact that habits taught at these ages can persist into adulthood. To successfully change activity habits in obese children research is needed on basic issues of activity planning, including the role of parental activity in child or adolescent activity, benefits of cross-training versus training on one activity, exercising alone compared with exercising in groups, and reducing access to sedentary behaviors that compete with being active.
Obese children choose to be sedentary rather than active(13,15), and the goal of research on the effects of exercise interventions in the treatment of childhood obesity should be to shift these patterns such that when given the opportunity, children will be active instead of sedentary. The most typical method for increasing exercise is to reinforce the child for being more active, which we have used in several treatment studies (18,20,21). However, the effects of reinforcement are often not maintained either because they are not implemented long enough to affect a permanent change in preference for active behaviors, or because they lose their effectiveness over time.
Another method for increasing the probability that a child or adolescent will be active is to reduce access to sedentary alternatives. For example, removing the television or computer games will stimulate the child or adolescent to find substitutes for these sedentary behaviors. If the environment provides easy access to active rather than sedentary alternatives, then active behaviors may be sampled, preferred, and eventually replace sedentary behaviors. However, just reducing access to sedentary behaviors may not be sufficient to change activity habits. It is possible that when the most preferred sedentary behaviors are made less accessible, then other sedentary behaviors will be more readily substituted for that preferred behavior than active behaviors. A sedentary child or adolescent who has television removed may substitute reading or listening to music rather than being active.
A good strategy to enhance activity may be to combine a powerful program that prompts active choices by reducing access to sedentary behaviors as well as providing more reinforcement for being active than being sedentary. This program should focus on creating environments that prompt activity, and reducing environments that prompt sedentary behaviors. Environments that should be targeted for study include the family, school and community recreational resources. In addition, this program should ensure that being active is more reinforcing than being sedentary, shifting motivation from being sedentary to exercising.
Adherence to exercise would be easy if interventions increased the reinforcing value of exercise. Some of the methods that have been used to improve adherence to exercise in adults may be useful, including increasing choice (48) and control over flexible exercise parameters(32), as well as providing immediate reinforcement during exercise, rather than after exercise completion (32). However, the reinforcing characteristics of sedentary behaviors may be especially strong in obese children or adolescents and conventional approaches such as offering choice and control over the exercise performed may not shift their preference to active behaviors or affect their adherence to an exercise program.
Exercise in the Prevention of Obesity
One potentially important extension of research on exercise in treating obesity is to use exercise to prevent obesity. Changes in activity, resulting in increased energy expenditure, may be particularly important in preventing obesity. Small errors in energy balance that could be related to the development of childhood or adolescent obesity may be corrected by increasing activity. While dietary changes may complement activity changes, it is also possible that for some children or adolescents increasing activity may be sufficient to prevent obesity.
It may be easier to shift activity in children who are not yet obese and prevent obesity rather than waiting until children are obese and then implementing exercise programs. In support of this idea we have shown that it is easier to shift choice from sedentary to active behaviors in nonobese than obese children (13). To successfully make changes in activity, obesity treatment programs should also focus on the extent to which current child and adolescent lifestyles revolve around major sedentary activities such as television watching and playing computer games(9). These activities can be very reinforcing, and can influence obesity in several ways. First, very reinforcing sedentary activities can compete with being active, and thus reduce daily energy expenditure (9). Second, sedentary activities such as watching television may prompt intake by the repeated commercials for food(29). Third, sedentary activities that are regularly paired with eating can become conditioned cues for eating, such that even if the child or adolescent were not hungry prior to engaging in the sedentary activity, the sedentary activity would cue eating. It might be worthwhile for parents to limit access to sedentary activities at times when active behaviors are more likely, or to limit sedentary behaviors until after active behaviors have been completed.
Prevention efforts should utilize school and community resources to increase knowledge about the importance of healthy eating and exercise. School lunch and physical education classes may be ideal situations for providing nonstigmatizing information about food and activity programs, as well as skill-based interventions for improving eating and activity habits that may lead to or contribute to obesity. Community resources, including community centers, recreational facilities, and churches, may be ideal settings for education and skills-based programs to promote exercise.
In summary, exercise is an important adjunctive treatment for childhood and adolescent obesity. Additional research is needed on the best type of exercise program that promotes added weight loss beyond that of diet alone and which promotes long-term changes in activity. Finally, this review has focused on using exercise in the treatment of children who are already obese. An equal, or even greater benefit of exercise programs may be in the prevention of obesity.
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Keywords:
ACTIVITY; OBESITY; CHILDREN; ADOLESCENTS; EXERCISE; WEIGHT LOSS
©1996The American College of Sports Medicine