Vegetarian Diets and Weight Reduction: a Meta-Analysis of Randomized Controlled Trials

Abstract

Vegetarian diets appeared to have significant benefits on weight reduction compared to non-vegetarian diets. Further long-term trials are needed to investigate the effects of vegetarian diets on body weight control.

Setting the Lipid Component of the Diet: A Work in Process

“…Vegetarian diets may result in substantial benefits in weight reduction and arterial blood pressure compared with nonvegetarian diets (3,72). Several types of vegetarian diets exist, including pesco-vegetarian (includes fish), lactovegetarian (includes eggs and dairy products) and vegan (includes no animal products).…”

Vegetarian Diets for Weight Loss: How Strong is the Evidence?

“…7 They identified 12 randomized trials with a total of 1151 participants (range: 11 to 291 per trial) that compared vegan diets (eight studies) or lacto-ovo diets (four studies) to non-vegetarian diets and that included body weight as a study outcome. Median study duration was only 18 weeks (range: 8 weeks to 2 years).…”

“…8 The group randomized to the Ornish diet, a low-fat vegetarian diet, had the lowest adherence (only 50 % compared to 65 % for Weight Watchers) and achieved non-significantly greater weight loss at 12 months (3.3 vs. 2.1 to 3.2 kg for other diets). 8 In Huang's metaanalysis, 7 the longest study lasted 24 months, assessed weight loss maintenance for a vegan vs. a moderate low-fat diet (from National Cholesterol Education Program), and showed significantly greater weight loss with the vegan diet at 1 year (4.9 vs. 1.8 kg) and 2 years (3.1 vs. 0.8 kg), with similar adherence rates between the two diets. 9 However, because few studies lasted longer than 6 months, this review was not able to assess the effects of vegetarian diets on long-term weight loss or maintenance.…”

“…7 Another recently published systematic review used network meta-analysis to compare weight loss outcomes in low-carbohydrate diets (such as Atkins and Zone), low-calorie diets (such as Weight Watchers) and lowfat diets (such as Ornish), but did not classify diets as vegetarian/vegan vs. non-vegetarian. The network meta analytic approach permitted comparisons of each diet against each other and against no diet; compared to no diet, weight loss was~8 kg at 6 months and~6 kg at 12 months for the various diets, with a similar effect for all diets, including the low-fat Ornish (vegetarian diet).…”

“…7 However, a meta-analysis is only as strong as the contributing trials. In this case, as in numerous other meta-analyses, the evidence base is relatively weak-just 12 trials, the majority of which were small in size and short in duration.…”