Vegetarian Diets Affect Weight Loss

Results from a recent study suggest vegetarian and vegan diets that don’t emphasize counting calories lead to more weight loss at 8 weeks and 6 months than diets including meat. The New DIETs (New Dietary Interventions to Enhance the Treatments for Weight Loss) study is the first randomized investigation to directly compare the effects of vegan, vegetarian, and omnivorous diets— without caloric restrictions—on body weight.

Researchers from the University of South Carolina randomly assigned 63 adults with a mean age of 49 years and a mean body mass index of 35 kg/m2 to 1 of 5 diets: vegan, vegetarian, pesco-vegetarian, semi-vegetarian, and omni-vegetarian.

All the dietary approaches emphasized low-fat, low-glycemic-index foods, but did not require caloric restriction. Participants attended weekly meetings to learn more about the type of diet they had been assigned, all of which stressed consumption of foods that were as unprocessed as possible. Analysis showed that, at 8 weeks, the groups adhering to a plant-based diet had lost an average of 8 to 10 pounds. Those consuming some meat lost an average of 5 pounds. At 6 months, the vegans had lost about 7 percent of their body weight.

The semi-vegetarian group had shed about 4 percent of their body weight, while the pesco-vegetarian and omnivorous groups each experienced about a 3 percent loss of body weight, on average. Study authors noted that the exact reason why individuals in the plant-based diet groups tended to experience greater weight loss was unclear, but the researchers theorized that changes in macronutrient content—found to be very different across groups (P < .05)—may have been a factor. The study findings may have bearing on the dietary recommendations physicians make to overweight and obese patients, says Gabrielle Turner-McGrievy, PhD, MS, RD, study author and assistant professor in the department of health promotion, education, and behavior at the Arnold School of Public Health at the University of South Carolina.

“While health practitioners generally recommend a standard low-calorie dietary approach to their patients, the use of a vegan or vegetarian diet, which does not impose energy intake restrictions or require dietary self-monitoring, may appeal to patients who have struggled with traditional weight-loss diets,” says Turner-McGrievy. The study also shows improvements in nutrient intake—particularly nutrients associated with cardiovascular disease—such as saturated fat, cholesterol, and fiber among participants following more plant-based approaches as opposed to traditional weight-loss approaches, she says.

“While not all patients will take to the idea of excluding meat from [their] diets, health practitioners can consider vegan and vegetarian diets to be another tool in our weight-loss toolbox.”

The study findings were originally presented during Obesity Week, the annual scientific meeting hosted by the Obesity Society and the American Society for Metabolic and Bariatric Surgery, held Nov. 12 – 16 in Atlanta.

—Mark McGraw