Randomised controlled trials (RCTs) of nutrition education interventions conducted in schools to reduce or prevent overweight in children and adolescents (aged five to 18 years) were eligible. Interventions had to be administered by health professionals or school teachers. Studies of children with eating disorders, dyslipidaemia, mental or physical disabilities, diabetes or anaemia were excluded. Studies of after-school interventions were excluded. The outcome of interest was body mass index (BMI).
Intervention components included educational games, classroom activities, school nutrition policy, parental involvement, social marketing and environmental changes. Only one trial reported on the theoretical framework used (theory of planned behaviour). Average participant age at baseline ranged from 8.2 years to 12.5 years. Most studies randomised participants at school level; some were randomised at class level. Trials were conducted in England, Italy, Norway, USA, China, Germany and Brazil.
Two reviewers independently selected studies for inclusion. Disagreements were resolved through consultation with a senior researcher.