Thirty-one RCTs (n=16,301) were included. Eighteen studies were rated high quality and 13 rated low quality. All of the included trials were RCTs. Individual trials included between 37 and 2,791 participants.
Body weight or body mass index (BMI) were reported in 20 studies, 14 of which were high quality and reported mixed findings. The reviewers concluded that there was no overall effect of the interventions on weight/BMI. Twelve studies reported weight/BMI in populations at risk and there was a strong evidence of an effect: six of seven high-quality RCTs showed a positive effect of interventions on body weight. There was no evidence of an effect of the interventions on weight/BMI among mixed populations. There was no evidence of an effect on weight/BMI for the three main types of intervention.
There was evidence for a positive effect on overall body fat (three high quality RCTs) and no evidence for an effect on central body fat, peripheral body fat (three high-quality RCTs) and hip circumference (two high-quality RCTs). There was limited evidence with respect to populations at risk for cardiovascular disease (one study). In mixed populations there was no evidence of an effect on central body fat (four high-quality RCTs) and hip circumference (two high-quality RCTs). Studies that included individual counselling (n=18) or group education (n=15) appeared to have more of an effect on peripheral body fat. Studies that evaluated exercise interventions (n=11) appeared to have more of an effect on overall body fat.
There was no evidence of a positive effect of the interventions on systolic or diastolic blood pressure overall and for any population or intervention subgroups.