A vegan diet is more effective for weight loss than a Mediterranean diet, according to a groundbreaking new study that compared the diets head to head. The randomized crossover trial, which was published in the Journal of the American College of Nutrition, found that a low-fat vegan diet has better outcomes for weight, body composition, insulin sensitivity, and cholesterol levels, compared with a Mediterranean diet.
The study randomly assigned participants—who were overweight and had no history of diabetes—to a vegan diet or a Mediterranean diet in a 1:1 ratio. For 16 weeks, half of the participants started with a low-fat vegan diet that eliminated animal products and focused on fruits, vegetables, whole grains, and legumes. The other half started with the Mediterranean diet, which followed the PREDIMED protocol, which focuses on fruits, vegetables, legumes, fish, low-fat dairy, and extra virgin olive oil, while limiting or avoiding red meat and saturated fats. Neither group had a calorie limit, and participants did not change exercise or medication routines, unless directed by their personal doctors. As part of the crossover design, participants then went back to their baseline diets for a four-week washout period before switching to the opposite group for an additional 16 weeks.
The study found that within 16 weeks on each diet:
- Participants lost an average of 6 kilograms (or about 13 pounds) on the vegan diet, compared with no mean change on the Mediterranean diet.
- Participants lost 3.4 kg (about 7.5 pounds) more fat mass on the vegan diet.
- Participants saw a greater reduction in visceral fat by 315 cm3 on the vegan diet.
- The vegan diet decreased total and LDL cholesterol levels by 18.7 mg/dL and 15.3 mg/dL, respectively, while there were no significant cholesterol changes on the Mediterranean diet.
- Blood pressure decreased on both diets, but more on the Mediterranean diet (6.0 mm Hg, compared to 3.2 mmHg on the vegan diet).
“Previous studies have suggested that both Mediterranean and vegan diets improve body weight and cardiometabolic risk factors, but until now, their relative efficacy had not been compared in a randomized trial,” says study author Hana Kahleova, MD, Ph.D., director of clinical research for the Physicians Committee. “We decided to test the diets head to head and found that a vegan diet is more effective for both improving health markers and boosting weight loss.”
The authors note that the vegan diet likely led to weight loss, because it was associated with a reduction in calorie intake, increase in fiber intake, decrease in fat consumption, and decrease in saturated fat consumption.
“While many people think of the Mediterranean diet as one of the best ways to lose weight, the diet actually crashed and burned when we put it to the test,” says study author Neal Barnard, MD, president of the Physicians Committee. “In a randomized, controlled trial, the Mediterranean diet caused no weight loss at all. The problem seems to be the inclusion of fatty fish, dairy products, and oils. In contrast, a low-fat vegan diet caused significant and consistent weight loss.”
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