Physical activity interventions in overweight and obese children & adolescents are associated with an improvement in body composition variables, including body weight, BMI, BMI z-score, fat mass percentage, waist circumference/central obesity. Despite the well accepted benefits of physical activity in the general population, specific pooled data in overweight and obese children and adolescents reveals only small effects. In this growing population, the trend is to increase weight with maturation, which may reduce observed reduction in BMI. Studies are also variable in the nature of the intervention, length of follow-up and chosen outcome variables. Many reviews include combined physical activity and other interventions (such as dietary education or modification).
Systematic review of meta-analyses (18 meta-analyses; 234 studies) including overweight and obese children and adolescents showed a small overall effect size of physical activity interventions1. Very small pooled effect sizes were demonstrated for body weight (g=-0.23; 95% CI -0.41 to –0.05; p=0.013; I2=35.8%), fat mass % (g=-0.38; 95% CI -0.55 to -0.21; p<0.001; I2=45.2%) and central obesity (waist circumference and/or waist:hip ratio) (g=-0.20; 95% CI -0.41 to -0.01; p=0.047; I2=0%). Medium effect size was demonstrated for reduction in BMI (g=-0.50; 95% CI -0.70 to -0.30; p=0.006; I2=77.5%). Subgroup analysis showed that aerobic interventions were associated with small improvements in all parameters, including improvement in BMI (g=-0.64) and visceral fat (g=-0.80), compared to resistance/combined interventions which were only associated with improvements in BMI (g=-0.31 (resistance-only), -0.40 (combined)) and BMI z-score (only combined programs, g=-0.97). Aerobic interventions of 4-12 weeks are effective in improving BMI, visceral fat and subcutaneous fat, and interventions with >1500 minutes total exercise duration also resulted in the additional benefit of reduced fat mass %.
Compared with aerobic activity alone, combined aerobic and resistance training was associated with greater reduction in body mass (mean difference -2.28kg) and fat mass (mean difference -4.34kg (-3.49%)), and greater increase in lean body mass (mean difference 2.20kg). This was more marked in interventions lasting >24 weeks (12 trials, n=555)2. A systematic review & meta-analysis by Kelley et al3 (34 studies, n=2239) reports a statistically significant reduction in BMI z-score for both combined aerobic & strength training (mean -0.11; 95% CI -0.19 to -0.03) and aerobic activity alone (mean -0.10; 95% CI -0.15 to -0.05) and in overweight and obese children and adolescents, compared to controls. No significant associated was found for strength training alone. Median exercise frequency was 3x/week, 50 mins/session over a 12-week period.
These results are consistent with a meta-analysis of structured exercise interventions for overweight and obese adolescents that found a moderate improvement in BMI (SMD 0.36; 95% CI 0.08 to 0.65)4. This was also reported in subgroup analysis of the Cochrane review of physical activity interventions for treatment of overweight or obese adolescents (12-17y)5. Analysis of 4 RCTs (n=117) demonstrated a reduction in BMI (Z=2.51; p=0.012). The International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE, including 7372 children aged 9-11y)6 reports the odds ratio (per standard deviation of the predictor variable) for accelerometer-measured moderate-vigorous activity and obesity as 0.49 (95% CI 0.44 to 0.55). Subgroup analysis demonstrated significant association between both moderate-vigorous activity and vigorous activity (OR 0.41; 95% CI 0.37 to 0.46) and obesity in all 12 study sites. Although this is a multi-national study conducted in 12 countries (including the UK) it is a cross-sectional study rather than a randomised controlled trial. Systematic review and meta-analysis of RCTs that used an active gaming intervention in obese and overweight children & adolescents (5-18y) revealed a statistically significant (although small) reduction in BMI (SMD -0.234; standard error 0.069). Average BMI z-score reduction was -0.181 (standard error 0.071)7. Greatest reduction in BMI was seen in studies involving participants with BMI ³30.
Systematic review of physical activity interventions in overweight and obese children aged between 10-18y (14 studies)8 demonstrated that, although effects on BMI were small and heterogeneous, improvement in BMI was most associated with supervised interventions. Subgroup analysis of physical activity-only interventions revealed a summary effect size of -0.36 (95% CI -0.64 to -0.08; p=0.539). Subgroup analysis in a Cochrane review of interventions to treat overweight and obese children aged 6-11y9 did not show any significant effect for physical activity alone for reduced BMI, BMI z-score, and body weight. This was also the case in a systematic review by Rajjo et al (133 RCTs, n=30 445) which reports that interventions involving multisport & aerobic exercise interventions alone did not lead to weight loss unless combined with diet or education10.
Quality of Evidence
Grade B – Moderate. There is evidence from large studies that physical activity is associated with improved body composition, but trials have inconsistencies and not all are RCTs.
Strength of Recommendation
Grade 1 – Strong – Evidence suggests that individuals will benefit from increased physical activity, with small improvements in body composition variables.
Longer-term physical activity interventions improve body composition in overweight and obese children and adolescents. Although statistically significant, the absolute values for body composition change are low. Despite this, the general health benefits for increased physical activity are well documented. Current evidence suggests that best results are achieved with structured interventions, including an aerobic component.
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