One positive quality meta-analysis (29 RCTs), four neutral quality RCTs and three observational studies (one positive, one neutral, one negative quality) provide strong evidence that weight management treatment with diet and cognitive-behavioral therapy given in a six-month initial intervention period, results in modest weight loss after follow-up of at least 18 months post-treatment. Attrition rates increased the longer the follow-up was conducted. This is a common weakness of these studies that may result in outcome bias.
