Background.
Overweight and obesity have negative health effects. Primary care clinicians are best placed to intervene in weight management. Previous reviews of weight loss interventions have included studies from specialist settings. The aim of this review was to estimate the effect of behavioural interventions delivered in primary care on body weight in overweight and obese adults.

Methods.
The review included randomized controlled trials (RCTs) of behavioural interventions in obese or overweight adult participants in a primary care setting, with weight loss as the primary outcome, and a minimum of 12 months of follow-up. A systematic search strategy was implemented in Medline, Embase, Web of Science and the Cochrane Central Registry of Controlled Trials. Risk of bias was assessed using the Cochrane Risk of Bias tool and behavioural science components of interventions were evaluated. Data relating to weight loss in kilograms were extracted, and the results combined using meta-analysis.

Results.
Fifteen RCTs, with 4539 participants randomized, were selected for inclusion. The studies were heterogeneous with respect to inclusion criteria and type of intervention. Few studies reported interventions informed by behavioural science theory. Pooled results from meta-analysis indicated a mean weight loss of −1.36kg (−2.10 to −0.63, P < 0.0001) at 12 months, and −1.23kg (−2.28 to −0.18, P = 0.002) at 24 months.

Conclusion.
Behavioural weight loss interventions in primary care yield very small reductions in body weight, which are unlikely to be clinically significant. More effective management strategies are needed for the treatment of overweight and obesity.