Current Sports Medicine Reports:
Do Youth Sports Prevent Pediatric Obesity? A Systematic Review and Commentary
Nelson, Toben F. ScD1; Stovitz, Steven D. MD, MS2; Thomas, Megan MPH, RD1; LaVoi, Nicole M. PhD3; Bauer, Katherine W. PhD1; Neumark-Sztainer, Dianne PhD1
1Division of Epidemiology and Community Health, University of Minnesota, Minneapolis, MN; 2Department of Family Medicine and Community Health, University of Minnesota, Minneapolis, MN; and 3School of Kinesiology, University of Minnesota, Minneapolis, MN
Address for correspondence: Toben F. Nelson, ScD, 1300 S. Second Street, Suite 300, Minneapolis, MN 55454 (E-mail: firstname.lastname@example.org).
Sport is a promising setting for obesity prevention among youth, but little is known about whether it prevents obesity. We reviewed research comparing sport participants with nonparticipants on weight status, physical activity, and diet. Among 19 studies, we found no clear pattern of association between body weight and sport participation. Among 17 studies, we found that sport participants are more physically active than those who do not participate. We found seven studies that compared the diet of sport participants with non-participants. These studies reported that youth involved in sport were more likely to consume fruits, vegetables, and milk, and also more likely to eat fast food and drink sugar-sweetened beverages and consume more calories overall. It is unclear from these results whether sports programs, as currently offered, protect youth from becoming overweight or obese. Additional research may foster understanding about how sport, and youth sport settings, can help promote energy balance and healthy body weight.
In the United States, approximately one in three children are either overweight or obese. Pediatric obesity is clearly a major public health problem in the United States and much of the world. Increasing physical activity and promoting a healthier dietary intake are the cornerstones of obesity prevention and treatment.
In the year 2000, the U.S. Secretaries of Health and Human Services and Education issued a joint report recommending sport participation as a strategy to increase energy expenditure, activity, and fitness among youth to promote health and prevent increasing levels of overweight among youth (54). The National Council of Youth Sports estimates that more than 44 million youth in the United States participate in sport, and more than half of high school students (56%) reported on the Youth Risk Behavioral Surveillance Survey that they participated on a school or community sport team (11). Youth sport programs are not designed or primarily intended to prevent obesity, but sports is a setting in which many youth are physically active. The physical activity involved in sport participation, combined with the high levels of participation, suggests that youth sport may be a promising setting for obesity prevention. Despite this promise, very little research or intervention efforts have focused on sports settings compared with research in other settings such as school and after-school programs. The available data indicate that those who participate in youth sport remain susceptible to overweight and obesity. For example, national studies in the United States have found that more than one in four youth sport participants (26% male and 27% female) were overweight (17), and nearly half of youth (48%) who were obese said they participated in sport (7).
To better understand the relationship between youth sport participation and obesity prevention, we systematically reviewed the existing research on the association between sport participation and body weight, plus two major determinants of obesity, physical activity, and dietary intake. Using the existing studies as a foundation, we highlight areas for future research and practice to help create youth sport settings that are more consistent with obesity prevention goals.
We (T.F.N. and M.T.) reviewed studies identified through searches of existing literature using the search engines PubMed and Google Scholar through February 2011 and using the terms "sport," "youth sport," and "sport participant." By youth, we specifically refer to elementary school through secondary school children who are approximately 6 to 18 years of age. Our definition of sport includes competitive and physical games or activities that have some degree of organization and are sponsored by a school or community group. However, most of the research we reviewed lacked precise or detailed measures of sport participation, and this is an important limitation. For the question of weight status, we used key words "weight," "overweight," "obese," and "body mass index." For the question of physical activity, key words "physical activity" and "exercise" were used, and for the question of diet, we used key words "nutrition," "dietary habits," "diet," "energy intake," and "sports drinks." We included studies that directly compared sport participants with those not participating in sport, as well as studies that employed within-subject designs that directly assessed the effects of sport participation. The primary reason for excluding articles identified in our search from this review was that they did not include a comparison of sport and nonsport conditions. In addition, studies that examined the relationship between sport participation and weight status, and statistically adjusted for physical activity, were excluded. Identified articles were cross-referenced with cited literature using ISI Web of Knowledge to ensure a comprehensive search.
Sport Participation and Weight Status
Our search identified 19 studies that explored the relationship between sport participation and weight status in children and adolescents. As shown in Table 1, most studies used cross-sectional designs with one study employing a longitudinal design.
Twelve studies found that sport participants had lower weight status than nonsport participants in at least one of the comparisons they examined (2,4,7,8,13,14,17,20,27,32,34,44). Several of these studies conducted multiple comparisons and found differences only among specific subgroups of the overall population. Seven studies found no association between sport participation and weight status (6,25,41,50,51,58,63). Overall, most of the comparisons indicated no difference between sport participants and nonparticipants. We examined whether patterns in the statistically significant findings existed by sex, age, sample size, or study outcome measure across all of these studies, and no clear pattern emerged. In particular, we suspected that studies with a larger sample size would be more likely to show differences between sport participants and nonparticipants. Among the 10 studies that had more than 1,000 study subjects, 24 comparisons were examined and only 9 of these showed significantly lower weight status among sport participants. Only one of these studies examined the type of sport youth were involved in and found that participants in some sports were more likely and in others were less likely to be overweight than nonparticipants (50). Sports with a higher level of obesity included rugby, swimming, judo, and tennis, and sports with lower levels of obesity included gymnastics, handball, horse riding, and dance, although the sample within each of these sports was relatively small. Another study found lower body mass index (BMI) among sport participants among females, but not males, participating in weight-related sports (e.g., gymnastics), while no differences existed between power team sport participants (e.g., football, soccer, hockey) and nonparticipants (13). One longitudinal study observed that males who participated in sport at age 11 to 12 years were less likely to be overweight at age 14, but no association between sport participation and weight status was observed among females or among males 14 to 17 years of age (27).
Two small intervention studies also are relevant to the question of sport participation and body weight. One study randomly assigned overweight and previously inactive youth to an after-school soccer program or a group that received health education and found significant increases in objectively measured physical activity and small but statistically significant decreases in BMI at 3 and 6 months in the soccer group compared to the health education group (60). A second, small quasi-experimental study found no differences in BMI between obese youth participating in a sport camp and support program and a control group (36).
The lack of a clear difference in weight status between participants and nonparticipants observed in some of the studies reviewed may be attributed to the type of sport studied and the specific body type suited for that sport. The wide variation in the prevalence of obesity between sports should be better understood in further research. Large body size is advantageous in some sports (e.g., American football). A study of high school football players found that 45% of offensive lineman were obese (≥95th percentile of BMI) (29). Most current and former adult professional football players meet standard criteria for obesity (53). Elite youth athletes in sports such as soccer and ice hockey tend to have advanced skeletal maturity, which is a risk factor for subsequent obesity (34). Unlike findings among adults, in children, there is a positive association between BMI and height (47). Children who are overweight tend to be tall, undergo less growth in height during adolescence, and have higher BMI as young adults (47). These forces may encourage selection of large children (who are at higher risk for future obesity) in competitive youth sport, particularly at early ages.
Several limitations exist with the studies on sport participation and weight status, including small sample size, use of BMI as an outcome measure, and use of cross-sectional designs. Small sample sizes may leave studies underpowered to observe differences, even if they do exist, between sport participants and nonparticipants. BMI is a reasonable measure of adiposity in children and adolescents (15), but it may not be a good indicator among sport participants, especially those who tend to be more muscular (37). Differential body composition may bias comparisons of sport participants and nonparticipants toward findings of no difference when using BMI, but the extent to which this issue is an important factor among youth is not known. Cross-sectional designs do not account for possible selection bias. For example, physically fit, normal-weight youth may be more likely to join and continue participating in sport, which may account for observed differences in weight status.
Given the limited available research, there is not sufficient evidence to conclude that sport participation protects against the development of obesity. Additional research is needed to understand weight status and weight gain among sport participants and to determine whether, and under what conditions, sport can effectively prevent unhealthy weight gain.
Sport Participation and Physical Activity
Table 2 presents a summary of studies, comparing physical activity levels of sport participants and nonparticipants. Both cross-sectional and longitudinal studies consistently show that youth who participate in sport are more likely to be physically active than nonparticipants (1,23,25-27,38-41,43-45,48,52,55,58,59). Longitudinal studies suggest that activity levels decline for many sport participants after they discontinue participation (1,6,26,40,48,52,55). These studies also suggest that the strength of the relationship between sport participation in adolescence and physical activity in adulthood is modest and does not occur in all subgroups.
Important information about the association of sport participation and physical activity levels can be garnered from two smaller studies evaluating a slightly different research question, namely, the direct contribution of sport to daily physical activity. One study examined self-reported activity to track energy expenditure during a 3-d period and found that males expended 20% and females expended 16% of their total daily energy in sport (30). A similar study of youth participating in a sports program objectively assessed activity using accelerometers on days when they did and did not participate in sport and found that sport contributed an additional 30 min of moderate and vigorous activity per day (59). Finally, a recent study that objectively assessed physical activity of youth sport participants in soccer, baseball, and softball found that fewer than one in four met recommended levels of activity during their sport team practice (30). This study found that sport participants, on average, were inactive for 30 min of their team practices.
Together, these studies suggest that participating in sport can help youth engage in more physical activity. However, there are important limitations to this literature. For example, the majority of studies used cross-sectional designs, thus making it unclear whether sport is causing the participants to be more active or whether more active children join sport programs. Many existing studies on sport and physical activity used self-reported measures rather than objective measurement of physical activity. Only one study identified in our search explored the factors that determine the amount of activity that occurs during youth sport, finding that activity varied by participant sex and type of sport (30). Instruction and motor skill development are important parts of many sport practices, and these may account for the sedentary time observed during sport in these studies. It is not clear from these studies how much of the sedentary time in sport was spent in these sport-related activities and it is also not clear what extent to which physical activity can be optimized in these settings without sacrificing instruction and skill development. These are topics for future research. Other relevant factors associated with physical activity during sport may include the amount of playing time, intensity level, skill level of players, coach expertise, practice organization and effectiveness, availability of appropriate equipment and facilities, and team/league policies (30). Each of these areas presents an opportunity for further research and may be amenable to interventions to influence physical activity and energy expenditure in youth sport.
Sport Participation and Dietary Intake
The majority of studies on diet among sport participants have focused on elite competitors or the female athlete triad (disordered eating, menstrual dysfunction, and low bone density), which may occur among athletes in sports that emphasize leanness (e.g., endurance sports, gymnastics) (35). We identified seven studies that compared sport participants and nonparticipants with respect to their dietary intake. These studies are summarized in Table 3.
The most comprehensive study to date comparing dietary intake of sport participants with nonparticipants found that youth involved in sport had better overall nutrient intake than youth not involved in sport (13). Other studies found that sport participants are more likely to report consuming fruits, vegetables, and milk than nonparticipants (10,23,48); however, sport participants appear to consume more overall calories than nonparticipants (10,14). One small study of male tennis players in Brazil found that nearly half the sample (45%) consumed more calories per day than they expended (24). Findings such as these may account for the lack of a clear effect of sport participation for preventing obesity.
Higher energy intake may be important for sport participants if energy expenditure is high but may lead to weight gain if energy intake exceeds expenditure. The available research suggests that excess calories consumed by youth sport participants may come from two sources: 1) fast food and 2) sugar-sweetened beverages such as soft drinks, fruit juices, and sports drinks (e.g., Gatorade and POWERADE). A study of middle and high school youth found a positive association between sports team participation and frequency of fast food consumption among males (18). A subsequent longitudinal analysis of these data found that, among males, sport team participation during middle school predicted greater fast food consumption into the high school years (5). Frequent fast food consumption is associated with greater intake of total calories, total fat, saturated fat, carbohydrates, sodium, added sugar, and sugar-sweetened beverages and lower intake of milk, fruits, and vegetables; higher weight; and weight gain (22). In other research, sport participants were more likely than nonparticipants to consume sports drinks and fruit juice and were equally likely to consume soft drinks (10). Consumption of sugar-sweetened beverages is associated with excess calorie intake, increased risk of overweight and obesity, weight gain, metabolic risk factors, and risk for type 2 diabetes (22). Sugar-sweetened beverage consumption among youth has risen during the past several decades, particularly among youth aged 6 to 11 years, and is associated with rapid increases in childhood obesity (56).
Our review of the studies that directly compare dietary habits of sport participants with nonparticipants found that the existing literature has several limitations. Most employed cross-sectional designs. It is possible that youth who are more inclined to participate in sport also are more likely to have a particular diet. The studies, in general, had limited assessment of dietary variables. Finally, all studies used self-reporting measures of diet. Additional research in this area could help identify possible areas for future intervention to improve eating behavior of sport participants.
Energy Balance in Youth Sport
Whether or not youth sport participation can effectively prevent overweight and obesity depends upon energy balance, a function of calorie consumption and physical activity. Although growing bodies require slightly more energy intake than expenditure, energy surplus and weight gain can occur when caloric intake exceeds expenditure. The best available estimates indicate that childhood obesity is driven by a surplus of approximately 110 to 165 kcal·d−1 for children ages 2 to 7 years and 678 to 1,017 kcal·d−1 for adolescents aged 12 to 17 years (57).
Little formal research has assessed energy balance in sport. Studies among elite athletes show that overall energy intake increases as activity levels and expenditure increase (42). While sport participants are more active than their peers who do not participate in sport, the benefits in terms of energy expenditure may be small since most of the time that youth spend in sport is either sedentary or in light-intensity activity (30,59). A study of youth participating in a school-based activity intervention found that youth may overcompensate for increased physical activity by eating more and gaining weight (46). If this commonly occurs in sport, it may account for why youth in sport are not less likely to be overweight or obese. The benefits of sport participation for obesity prevention are dependent on the actual amount of energy expended in sport and must be considered in the context of dietary habits of sport participants.
Youth May Be Unprepared to Start Playing Sport
One challenge to making sport an effective setting for obesity prevention is that some youth may be unprepared for involvement in sport because they are already overweight. Youth who master fundamental skills of movement such as running, catching, throwing, and balancing are more likely to continue being physically active and less likely to be overweight (32), while overweight youth may have poor fitness levels and underdeveloped motor skills that leave them at a disadvantage when beginning sport. This situation is compounded by the lack of formal physical education and other opportunities to engage in physical activity during the school day in many public schools in the United States (28). Youth who are in this circumstance may need remedial efforts to improve their fitness and motor skill development before they are able to begin competing in sport at the same level with their peers. These factors are likely to influence whether youth are involved with sport at all and also whether they are likely to prematurely drop out of sport. Little research has examined the contribution of these factors to pediatric obesity at a population level.
Foods and Beverages in Youth Sport
Candy, confectionary, sugar-sweetened beverages (including sport drinks), and ice cream are commonly sold at youth sport events or brought to the event by contestants and parents (10). Youth sport marketing is a key part of food and beverage marketing strategies, and voluntary industry guidelines may actually encourage food and beverage companies to associate those products with health and fitness activities such as youth sport (61). Sports drinks such as Gatorade and POWERADE are commonly marketed to, and used by, youth sport participants. Among some sport teams and leagues, the practice of providing snacks and beverages is institutionalized, wherein volunteer parent coordinators develop and assign a snack schedule. The snacks and beverages provided are often packaged convenience food (e.g., sport drinks, soda pop, candy bars, cookies, chips, "fruit" snacks) and, in combination, could total 300 to 500 calories or more. A recently published report from the Committee on Nutrition and the Council on Sports Medicine and Fitness recommended that children avoid sports and energy drinks during meals, snacks, and as a replacement for low-fat milk or water because they increase the risk for overweight or obesity in children and adolescents (12).
In addition to direct access to excess calories available in sport settings, participants are subject to time pressures associated with attending sport practices and events. Time pressures may lead to more consumption of fast food and other processed food, which tend to be convenient but less healthy options (18). Regular family meals are associated with healthful dietary behaviors but may be sacrificed due to sport participation (9). Parents of youth sport participants report that sport-related time pressures influence meal planning and preparation, interfering with family meals (19).
Weight Status, Physical Activity, and Diet - When Youth Drop Out of Sport
Participation in youth sport has a modest, positive association with adult physical activity and exercise habits, even for those who are no longer involved in sport (49,55). However, sport dropout is common during adolescence into young adulthood and associated with declines in physical activity (49,55). A few studies have examined the impact of dropping out of sport on future dietary intake and weight status. One study of adult women found no relationship between history of sport participation as a youth and either total daily caloric intake or proportion of calories from fat (2). A study from Finland found that adults who participated in youth sport were less likely to meet the criteria for metabolic syndrome than those who never participated in sport, but the group that dropped out of sport was at a higher risk than those who had sustained participation (62).
Dropout from youth sport occurs for a variety of reasons, including personal factors such as lack of enjoyment or motivation, time constraints, pressure to perform, and low achievement orientation and organizational factors such as coaching issues, lack of playing time, and lack of opportunities to participate (22,45). These specific reasons youth drop out of sport may differ by age, competition level, sport, and gender, and additional research is needed in this area (22). Regardless of the reason for dropping out of sport, decreasing energy expenditure without replacement with other forms of physical activity and/or decreasing caloric intake can promote energy surplus and weight gain. Childhood eating patterns help establish adult dietary habits, and these findings highlight the importance of promoting good nutrition in conjunction with youth sports. Whether youth sport participation predicts future dietary intake is understudied and warrants further research.
Promoting Energy Balance in Youth Sport
Despite the lack of research on obesity prevention in youth sport, opportunities exist for facilitating energy expenditure and limiting energy intake from sources of low nutritional value in these settings. It is important to recognize that youth sport coaches and league administrators are often volunteers with little formal training in physical education, coaching, or nutrition. It is not reasonable to expect them to intervene in an area where they are not trained or experienced. Youth, parents and coaches may have little or no awareness of the large number of calories contained in snacks and beverages commonly offered in youth sport settings or the relatively small number of calories children expend during sport. One potential intervention approach is to develop training and education materials for youth coaches in an accessible format. These materials could help coaches become more aware of energy balance in youth sport and emphasize ways to organize and structure practices and events to maximize physical activity, limit sedentary time, and promote healthy eating during youth sport. Other opportunities exist to reach youth coaches through seminars and clinics. Guidelines for minimum education and qualifications to coach youth sport could be established for the promotion of activity and healthy eating in youth sport. In addition, many leagues sell foods and beverages with high caloric content and low nutritional value to fund youth sport while overlooking their potential deleterious effects on child health. The Institute of Medicine recognized the potential for food and beverage sales in youth sport to contribute to the childhood obesity epidemic and recommended that programs encourage the sale of healthier options in youth sport venues. However, no system or guidelines are currently in place to monitor or enforce these standards. Other simple interventions for youth sport leagues include the development of guidelines for fundraising and for parents who organize postgame snacks to include health-promoting products. Existing research and experience in other settings such as schools and after-school programs can help guide recommendations and interventions. Regulation of advertising and sponsorship in youth sport could be implemented by either governmental or youth sport governing bodies.
Aside from providing guidance, physicians can help through direct patient care. A preparticipation examination is generally required for sports at the high school level and occasionally required in youth sport leagues during the early teenage years. The preparticipation physical offers an excellent opportunity for physicians to offer their patients tailored advice about activity, nutrition, and obesity prevention for sport. The American College of Sports Medicine has issued a consensus statement that encourages team physicians to evaluate the weight status, nutritional needs, and training habits of adolescent athletes; provide appropriate counseling on nutrition and exercise; as well as monitor athletes' weight status (3). Physicians should aim to identify problems before they manifest as excess weight or related health consequences. They should also anticipate the high dropout rate from sport as youth move into adulthood and consider the likelihood that youth will not be involved in sport in the future in their advice. All sport participants should be advised by their physicians to regularly engage in behaviors to avoid excess weight gain. Physicians can establish better links with athletes, parents, and coaches to increase their awareness of issues related to energy balance in youth sport and recommend strategies for maintaining healthy weight.
Sport is beneficial for youth as it provides a setting for engaging in physical activity, interacting with adults and peers, and developing a variety of physical and social skills. Many features of youth sport make it a natural setting for pursing obesity prevention goals. Currently, it is unclear whether youth sport effectively works to prevent the development of pediatric obesity. Youth participating in sport are more physically active than those who do not participate, and sport participation should be encouraged on this basis. However, the existing research suggests that youth in sport are more likely to consume greater amounts of calories and consume some unhealthy foods and beverages. It is unclear whether the higher energy expenditure associated with sport compensates adequately for this additional energy intake.
More research is needed to better understand and identify a possible role for sport participation in obesity prevention. Future research efforts could include the direct comparison of energy expenditure and energy intake among participants, an assessment of how food and drinks consumed in sport settings contributes to total daily caloric intake, and whether youth compensate for that consumption through additional activity or reduced caloric intake at other meals. Appropriate measures to assess sport participation are needed to understand the potential sources of variation within sport that may impact weight status, physical activity, and diet, including type of sport, playing time, intensity level, skill level, practice effectiveness, coach expertise, availability of appropriate programs, equipment, facilities, and availability of food in sport settings. Much of the existing research involves studies with cross-sectional design. More research that incorporates longitudinal assessment of sport participation, weight status, physical activity, and diet with studies specifically designed to study the contribution of sport participation is needed. These study designs also will shed light on the effects of dropping out of sport on physical activity, diet, and weight status. Small intervention studies also are needed to assess the effects of modifications to sport programs on weight status, physical activity, and diet.
There are many opportunities to encourage sport participants to be even more active during their practices and to improve their dietary intakes. Participants, parents, coaches, league administrators, and physicians are important target audiences for awareness and intervention. Additional discussions among key stakeholders are needed, and interventions to reduce the exposure to the excessive calories and other unhealthy food and beverage options available in youth sport must occur before the promise of obesity prevention in youth sport can be realized.
The authors declare no conflict of interest.
This study was conducted within the Transdisciplinary Research on Energetics and Cancer initiative, a consortium of research centers funded by the National Cancer Institute and, specifically, by a Career Development Award to T.F. Nelson, ScD, through the Transdisciplinary Research on Energetics and Cancer grant U54CA116849 at the University of Minnesota.
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© 2011 American College of Sports Medicine
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