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Evidence Summary

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Vegetarian diets, particularly vegan diets, help with weight loss.

Huang RY, Huang CC, Hu FB, et al. Vegetarian diets and weight reduction: a meta-analysis of randomized controlled trials J Gen Intern Med. 2015;31:109-16.

Review question

Does a vegetarian diet help adults to reduce body weight? Is there a difference between lacto-ovo-vegetarian and vegan diets.

Background

Obesity is a growing public health concern, and increases the risk of a number of diseases. A vegetarian diet can reduce the risk of diabetes, heart disease and death, and may help to reduce body weight. There are several types of vegetarian diets, and it is not known which one might be the most effective for weight loss.

How the review was done

  • This review includes 12 randomized controlled trials of 1151 participants, ranging from age 18 to 82 years. Five studies were high quality, and 7 studies were low quality.
  • Six studies only included participants who had overweight or obesity at the beginning of the study, five studies only included those with Type 2 diabetes, and one study only included those with arthritis.
  • Eight studies compared a vegan diet to a control diet. A vegan diet is one in which no animal products are eaten.
  • Four studies compared a lacto-ovo-vegetarian diet to a control diet. A lacto-ovo-vegetarian diet is one in which no meat is eaten, but milk and eggs are included.
  • The control diets included low-fat, anti-diabetes, and weight reduction diets.
  • In all studies, researchers compared the amount of weight loss in participants following the vegetarian diet to those following the control diet.

What the researchers found

Those who ate a vegetarian diet lost an average of 2.0 kg more than those who followed a control diet. The vegan diet was more effective than the lacto-ovo-vegetarian diet. Combining a vegetarian diet with a decrease in calories was more effective than a vegetarian diet alone. Studies that were less than one year were more effective than those that were more than one year.

Conclusion

Vegetarian diets are effective for weight loss, and a vegan diet is more effective than a lacto-ovo-vegetarian diets. Combining a vegetarian diet with a decrease in calories is the most effective for weight loss. Longer studies are needed to understand the long-term effects of these diets. 

 

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Glossary

Randomized controlled trials
Studies where people are assigned to one of the treatments purely by chance.

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