Box 2: Inclusion and exclusion criteria.

Studies were included if they met the following criteria:
• Behavioural (diet, exercise, social support or lifestyle strategies alone or in combination) trial of weight gain prevention
• Minimum 12-week intervention involving children or youth aged 0–18 years who were normal or mixed weight
• Randomized controlled trial with a no intervention, usual practice or minimal component (e.g., single newsletter or information session on general health) comparison group
• Reported data for one or more specified weight outcomes (i.e., change in BMI, BMI z-score, or prevalence of overweight or obesity)
• Reported data for weight outcomes of interest at least 12 weeks postbaseline assessment
• No restrictions on study design, comparison group, reporting of weight outcomes or timing of assessment were applied to studies that reported data for harms of interventions
• Results were published in English or French

Studies were excluded for the following reasons:
• Intervention involved surgical procedures, medications or was intended to treat obesity
• Intervention targeted only obese children and youth (treatment of obesity), involved a population with serious illness or comorbidity, or pregnant adolescents
• Intervention was conducted in an in-patient hospital setting (excluded as representing a level of intervention not feasible for prevention)
• Results were published in a language other than English or French