Comparative effectiveness of plant-based diets for weight loss: a randomized controlled trial of five different diets.

OBJECTIVE: The aim of this study was to determine the effect of plant-based diets on weight loss. METHODS: Participants were enrolled in a 6-mo, five-arm, randomized controlled trial in 2013 in South Carolina. Participants attended weekly group meetings, with the exception of the omnivorous group, which served as the control and attended monthly meetings augmented with weekly e-mail lessons. All groups attended monthly meetings for the last 4 mo of the study. Diets did not emphasize caloric restriction. RESULTS: Overweight adults (body mass index 25-49.9 kg/m(2); age 18-65 y, 19% non-white, and 27% men) were randomized to a low-fat, low-glycemic index diet: vegan (n = 12), vegetarian (n = 13), pesco-vegetarian (n = 13), semi-vegetarian (n = 13), or omnivorous (n = 12). Fifty (79%) participants completed the study. In intention-to-treat analysis, the linear trend for weight loss across the five groups was significant at both 2 (P < 0.01) and 6 mo (P < 0.01). At 6 mo, the weight loss in the vegan group (-7.5% ± 4.5%) was significantly different from the omnivorous (-3.1% ± 3.6%; P = 0.03), semi-vegetarian (-3.2% ± 3.8%; P = 0.03), and pesco-vegetarian (-3.2% ± 3.4%; P = 0.03) groups. Vegan participants decreased their fat and saturated fat more than the pesco-vegetarian, semi-vegetarian, and omnivorous groups at both 2 and 6 mo (P < 0.05). CONCLUSIONS: Vegan diets may result in greater weight loss than more modest recommendations.

Randomization to plant-based dietary approaches leads to larger short-term improvements in Dietary Inflammatory Index scores and macronutrient intake compared with diets that contain meat.

Studies have examined nutrient differences among people following different plant-based diets. However, all of these studies have been observational. The aim of the present study was to examine differences in nutrient intake and Dietary Inflammatory Index (DII) scores among overweight and obese (body mass index 25.0-49.9 kg/m(2)) adults randomized to receive dietary instruction on a vegan (n = 12), vegetarian (n = 13), pescovegetarian (n = 13), semivegetarian (n = 13), or omnivorous (n = 12) diet during a 6-month randomized controlled trial. Nutrient intake, nutrient adequacy, and DII score were assessed via two 24-hour dietary recalls (Automated Self-Administered 24-Hour Dietary Recall) at baseline and at 2 and 6 months. Differences in nutrient intake and the DII were examined using general linear models with follow-up tests at each time point. We hypothesized that individuals randomized to the vegan diet would have lower DII scores and greater improvements in fiber, carbohydrate, fat, saturated fat, and cholesterol at both 2 and 6 months as compared with the other 4 diets. Participants randomized to the vegan diet had significantly greater changes in most macronutrients at both time points, including fat and saturated fat, as well as cholesterol and, at 2 months, fiber, as compared with most of the other diet groups (Ps < .05). Vegan, vegetarian, and pescovegetarian participants all saw significant improvements in the DII score as compared with semivegetarian participants at 2 months (Ps < .05) with no differences at 6 months. Given the greater impact on macronutrients and the DII during the short term, finding ways to provide support for adoption and maintenance of plant-based dietary approaches, such as vegan and vegetarian diets, should be given consideration.

Low glycemic index vegan or low-calorie weight loss diets for women with polycystic ovary syndrome: a randomized controlled feasibility study.

The aim of this randomized pilot was to assess the feasibility of a dietary intervention among women with polycystic ovary syndrome (PCOS) comparing a vegan to a low-calorie (low-cal) diet. Overweight (body mass index, 39.9 ± 6.1 kg/m(2)) women with PCOS (n = 18; age, 27.8 ± 4.5 years; 39% black) who were experiencing infertility were recruited to participate in a 6-month randomized weight loss study delivered through nutrition counseling, e-mail, and Facebook. Body weight and dietary intake were assessed at 0, 3, and 6 months. We hypothesized that weight loss would be greater in the vegan group. Attrition was high at 3 (39%) and 6 months (67%). All analyses were conducted as intention-to-treat and presented as median (interquartile range). Vegan participants lost significantly more weight at 3 months (-1.8% [-5.0%, -0.9%] vegan, 0.0 [-1.2%, 0.3%] low-cal; P = .04), but there was no difference between groups at 6 months (P = .39). Use of Facebook groups was significantly related to percent weight loss at 3 (P < .001) and 6 months (P = .05). Vegan participants had a greater decrease in energy (-265 [-439, 0] kcal/d) and fat intake (-7.4% [-9.2%, 0] energy) at 6 months compared with low-cal participants (0 [0, 112] kcal/d, P = .02; 0 [0, 3.0%] energy, P = .02). These preliminary results suggest that engagement with social media and adoption of a vegan diet may be effective for promoting short-term weight loss among women with PCOS; however, a larger trial that addresses potential high attrition rates is needed to confirm these results.