Abstract: We included 20 RCTs, including 3057 participants. The number of participants ranged per trial between 15 and 645. Follow-up ranged between 24 weeks and two years. Eighteen trials were parallel RCTs and two were cluster RCTs. Twelve RCTs had two comparisons and eight RCTs had three comparisons. The interventions varied widely; the duration, content, delivery and follow-up of the interventions were heterogeneous. The comparators also differed. This review categorised the comparisons into four groups: parent-only versus parent-child, parent-only versus waiting list controls, parent-only versus minimal contact interventions and parent-only versus other parent-only interventions. Trial quality was generally low with a large proportion of trials rated as high risk of bias on individual risk of bias criteria. In trials comparing a parent-only intervention with a parent-child intervention, the body mass index (BMI) z score change showed a mean difference (MD) at the longest follow-up period (10 to 24 months) of -0.04 (95% confidence interval (CI) -0.15 to 0.08); P = 0.56; 267 participants; 3 trials; low quality evidence. In trials comparing a parent-only intervention with a waiting list control, the BMI z score change in favour of the parent-only intervention at the longest follow-up period (10-12 months) had an MD of -0.10 (95% CI -0.19 to -0.01); P = 0.04; 136 participants; 2 trials; low quality evidence. BMI z score change of parent-only interventions when compared with minimal contact control interventions at the longest follow-up period (9 to 12 months) showed an MD of 0.01 (95% CI -0.07 to 0.09); P = 0.81; 165 participants; 1 trial; low quality evidence. There were few similarities between interventions and comparators across the included trials in the parent-only intervention versus other parent-only interventions and we did not pool these data. Generally, these trials did not show substantial differences between their respective parent-only groups on BMI outcomes. Other outcomes such as behavioural measures, parent-child relationships and health-related quality of life were reported inconsistently. Adverse effects of the interventions were generally not reported, two trials stated that there were no serious adverse effects. No trials reported on all-cause mortality, morbidity or socioeconomic effects. All results need to be interpreted cautiously because of their low quality, the heterogeneous interventions and comparators, and the high rates of non-completion. Parent-only interventions may be an effective treatment option for overweight or obese children aged 5 to 11 years when compared with waiting list controls. Parent-only interventions had similar effects compared with parent-child interventions and compared with those with minimal contact controls. However, the evidence is at present limited; some of the trials had a high risk of bias with loss to follow-up being a particular issue and there was a lack of evidence for several important outcomes. The systematic review has identified 10 ongoing trials that have a parent-only arm, which will contribute to future updates. These trials will improve the robustness of the analyses by type of comparator, and may permit subgroup analysis by intervention component and the setting. Trial reports should provide adequate details about the interventions to be replicated by others. There is a need to conduct and report cost-effectiveness analyses in future trials in order to establish whether parent-only interventions are more cost-effective than parent-child interventions.

Plain-language summary: We found 20 randomised controlled trials (clinical studies where people are randomly put into one of two or more treatment groups) comparing diet, physical activity and behavioural (where habits are changed or improved) treatments (interventions) to a variety of control groups (who did not receive treatment) delivered to parents only of 3057 children aged 5 to 11 years. There were few similarities between the trials in the nature and types of interventions used. We grouped the trials by the type of comparisons. Our systematic review reported on the effects of the parent-only interventions compared with parent and child interventions, waiting list controls (where the intervention was delayed until the end of the trial), other interventions with only minimal information or contact and other types of parent-only interventions. The children in the included trials were monitored (called follow-up) for between six months and two years. This evidence is up to date as of March 2015. The most reported outcome was the body mass index (BMI). This is a measure of body fat and is calculated by dividing weight (in kilograms) by the square of the body height measured in metres (kg/m2). The studies measured BMI in ways that took account of gender, weight and height as the children grew older (such as the BMI z score and the BMI percentile). When compared with a waiting list control, there was limited evidence that parental interventions helped to reduce BMI. In looking at the longest follow-up periods of the included trials, we did not find firm evidence of an advantage or disadvantage of parent-only interventions when compared with either parent and child interventions, or when compared with limited information. Our review found very little information about how different types of parental interventions compared. No trial reported on death from any cause, illness or socioeconomic effects (such as whether parent-only interventions are lower in costs compared with parent and child interventions). Two trials reported no serious side effects and the rest of the trials did not report whether side effects occurred or not. Information on parent-child relationships and health-related quality of life was rarely reported. The overall quality of the evidence was low, mainly because there were just a few trials per measurement or the number of the included children was small. In addition, many children left the trials before they had finished.