Twenty-one studies (74,862 participants) were included in the review: one retrospective uncontrolled cohort study (5,503 participants), one serial cross-sectional study (63,318 participants), four cluster randomised controlled trials (RCTs) (3,120 participants) and 15 RCTs (2,921 participants). Eighteen studies were rated as strong quality. One study was of moderate quality and two were of weak quality (all three of these were the studies with societal-level interventions).
Individual-level interventions (one cluster RCT, four RCTs): Mixed findings (demonstrating a reduction or no change) were reported in relation to body weight (five trials) and body mass index (two trials). Two trials demonstrated no change in waist circumference (two trials). Two trials reported positive intervention effects that reduced socioeconomic inequalities related to obesity; three reported no intervention effect or no effect on the socioeconomic gradient related to obesity.
Community-level interventions (two cluster RCTs, 11 RCTs): Mixed findings were reported in relation to changes in body weight (nine trials) and body mass index (seven trials) and most studies reported no change in these outcomes following intervention. Three trials reported positive intervention effects that reduced socioeconomic inequalities related to obesity; the rest reported no intervention effect or no effect on the socioeconomic gradient related to obesity.
Societal-level interventions (one cluster RCT, one retrospective cohort study, one serial cross-sectional study): No changes were reported for body mass index (two studies) and body weight (one study). Two trials reported no intervention effect or no effect on the socioeconomic gradient related to obesity. The impact of one study intervention was unclear.
Further results were reported.