Plant-Based Diets Show More Weight Loss Without Emphasizing Caloric Restriction

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Most weight-loss interventions focus on reducing calories, but a new study shows that vegan and vegetarian dietary patterns can result in more weight loss than those that include meat without emphasizing caloric restriction. The study, “How Plant-Based Do We Need to Be to Achieve Weight Loss? Results of the New Dietary Interventions to Enhance the Treatments for Weight Loss (New DIETs) Study,” also emphasizes the importance of incorporating low-fat and low-glycemic index foods. Results of the award-winning study are being presented today at a special session of The Obesity Society (TOS) Annual Meeting at ObesityWeek 2013 for the five finalists of the TOS Ethan Sims Young Investigator Award.

“Many researchers agree that vegan eating styles are tied to lower BMI, lower prevalence of type 2 diabetes, and less weight gain with age,” said lead researcher Brie Turner-McGrievy, PhD, of the University of South Carolina. “This is the first randomized study that directly compares how vegan, vegetarian, and omnivorous dietary patterns that do not emphasize caloric restriction can impact body weight. We found that participants consuming vegan and vegetarian diets lost an average of 8.2 to 9.9 pounds over eight weeks while those consuming some meat lost 5.1 pounds.”

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%, omnivorous: ‑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. 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.”

Limitations of this study include the small sample size and timeframe of evaluation. Results of the six-month follow-up assessments of participants to determine long-term adherence will also be presented today.

Find more information on the study in the meeting abstracts here.