Forty-six studies of 61 obesity prevention programmes were included (n=23,172). There was random assignment of participation in 51 programmes.
Thirteen interventions evaluated in 14 trials showed a statistically significant effect of the intervention. The mean effect size was small (r=0.04), but was significantly higher than zero (p=0.01). The range of effect sizes was -0.24 to 0.50. There was statistically significant heterogeneity between the studies (p<0.001).
An extensive investigation of potential factors moderating the effect size for interventions was reported. This suggested that interventions were more effective in trials enrolling children over 11 years and adolescents (r=0.07, p<0.05) than in those enrolling pre-adolescents (r=0.03, p=0.07), and that effect sizes were also larger in trials with female participants (r=0.13, p<0.01) than in those conducted with mixed or male populations (r=0.02, p=0.06). Interventions with a shorter duration (less than 16 weeks) also appeared to be more effective (r=0.06, p<0.01), as were interventions solely focused on weight change (r=0.09, p<0.001). Trials with self-selecting recruitment also showed larger effect sizes (r=0.14, p<0.001) than population-based interventions, for which effect sizes did not differ from zero (r=0.02, p=0.10).
Variables found to be significant predictors of effect size were entered into a multivariate model. Only age and self-selected recruitment were found to be statistically significant in the multivariate model.