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Review
. 2016 Jan;31(1):109-16.
doi: 10.1007/s11606-015-3390-7.

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

Ru-Yi Huang  1   2   3 , Chuan-Chin Huang  4 , Frank B Hu  4   5 , Jorge E Chavarro  6   7
Affiliations
Review

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

Ru-Yi Huang et al. J Gen Intern Med. 2016 Jan.

Abstract

Background: Vegetarian diets may promote weight loss, but evidence remains inconclusive.

Methods: PubMed, EMBASE and UpToDate databases were searched through September 22, 2014, and investigators extracted data regarding study characteristics and assessed study quality among selected randomized clinical trials. Population size, demographic (i.e., gender and age) and anthropometric (i.e., body mass index) characteristics, types of interventions, follow-up periods, and trial quality (Jadad score) were recorded. The net changes in body weight of subjects were analyzed and pooled after assessing heterogeneity with a random effects model. Subgroup analysis was performed based on type of vegetarian diet, type of energy restriction, study population, and follow-up period.

Results: Twelve randomized controlled trials were included, involving a total of 1151 subjects who received the intervention over a median duration of 18 weeks. Overall, individuals assigned to the vegetarian diet groups lost significantly more weight than those assigned to the non-vegetarian diet groups (weighted mean difference, -2.02 kg; 95 % confidence interval [CI]: -2.80 to -1.23). Subgroup analysis detected significant weight reduction in subjects consuming a vegan diet (-2.52 kg; 95 % CI: -3.02 to -1.98) and, to a lesser extent, in those given lacto-ovo-vegetarian diets (-1.48 kg; 95 % CI: -3.43 to 0.47). Studies on subjects consuming vegetarian diets with energy restriction (ER) revealed a significantly greater weight reduction (-2.21 kg; 95 % CI: -3.31 to -1.12) than those without ER (-1.66 kg; 95 % CI: -2.85 to -0.48). The weight loss for subjects with follow-up of <1 year was greater (-2.05 kg; 95 % CI: -2.85 to -1.25) than those with follow-up of ≥1 year (-1.13 kg; 95 % CI: -2.04 to -0.21).

Conclusions: 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.

Keywords: Energy restriction; Lacto-ovo-vegetarian diet; Obesity; Overweight; Vegan diet.

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Figures

Fig. 1
Fig. 1
Study flow diagram. RCT randomized controlled trial
Fig. 2
Fig. 2
Pooled weighted mean differences in weight reduction between vegetarian and non-vegetarian diets. Effects on estimated weight reduction for each study depicted as solid squares; error bars indicate 95 % CIs. The pooled estimate of −1.99 kg (95 % CI, −2.72 to −1.25) of weight loss is shown as the diamond. RE random effect, Weight inverse variance weight, WMD weighted mean difference, CI confidence interval
Fig. 3
Fig. 3
Pooled weighted mean differences in weight reduction by subgroup. Effects on estimated weight reduction for each study depicted as solid squares; error bars indicate 95 % CIs. The pooled estimate of weight loss is shown as the diamond. RE random effect, Weight inverse variance weight, WMD weighted mean difference, CI confidence interval. A. Vegan diets vs. lacto-ovo-vegetarian (LOV) diets. Vegan diets were defined as avoiding all animal products, whereas lacto-ovo-vegetarian diets avoided meat but consumption of milk and eggs was allowed. B. Energy restriction vs. no energy restriction group. C. Follow-up < 1 year vs. ≥ 1 year. D. General population vs. overweight or obese population. Normal represents general population including normal-weight, overweight and obese individuals
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Comment in

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