Effects of vegetable consumption on weight loss: a review of the evidence with implications for design of randomised controlled trials

Vegetable consumption is a key strategy in many weight loss programs but establishing the evidence that vegetable consumption per se assists with weight loss may be difficult. Creating a dietary energy deficit involves the whole diet, so research on the effects of vegetables may need to consider the whole-dietary model. The aims of this review were to examine the evidence on whether a higher vegetable consumption resulted in greater weight loss in overweight adults (compared to lower intakes) in view of a critique study designs with respect to their potential impact on outcomes. Using the PubMed search engine, a systematic review of randomized controlled trials (RCTs) published in the period 1988 to 2011 was conducted. Of the 16 RCTs scrutinized, five reported greater weight loss, nine no difference, one showed weight gain, and one reported a positive association between weight loss and high vegetable consumption. Trials which showed beneficial effects compared a healthy high vegetable diet with a control diet based on usual consumption patterns, and/or included behavioral support and counseling. On face value, the evidence reviewed appeared inconclusive but closer examination of study designs exposed important implications for RCTs that examine effects of foods on weight loss.