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The eight-week pilot study compared adoption of five different dietary approaches: vegan, vegetarian, pesco-vegetarian, semi-vegetarian, or omnivorous, on weight loss in 63 adults affected by obesity or overweight. All dietary patterns emphasized eating low-fat and low-glycemic index foods. Mean (SD) percent weight loss was significantly different among the five groups (vegan: -4.8+-2.1%, vegetarian: -4.8+-3.2%, pesco-vegetarian: -4.3+-1.8%, semi-vegetarian: -3.7+-2.3%, omni-vegetarian: -2.2+-2.0%, intention-to-treat analysis; p<0.05).


The reason for greater weight loss in the vegan and vegetarian groups remains to be studied, but may be due to changes in macronutrient content as macronutrients (percent kcal) were found to be significantly different across groups, with the vegan group having the lowest saturated fat. In addition, participants in this study most likely ate fewer calories as a result of the dietary changes they made to consume more vegan or vegetarian meals.


Dr. Turner-McGrievy continued, “Diets that focus primarily on calorie restriction are a cornerstone of weight loss programs; however, they usually involve dietary self-monitoring, which many individuals find burdensome and can limit adherence.”


Because weight loss achieved by patients following plant-based diets in this study occurred without emphasizing caloric restriction, some individuals may find these types of dietary patterns easier to follow over the long term, according to the researchers.


“This pilot study could have implications for those struggling to cut back on calories to lose weight,” said Adam Tsai, MD, TOS Public Affairs Committee Chair and Assistant Professor at the University of Colorado. “These results show that weight loss can be achieved by following vegan and vegetarian dietary patterns that do not focus primarily on calorie restriction.”