Vegan Diet Bests Mediterranean Diet for Inducing Weight Loss, Lowering Cholesterol

Hana Kahleova, MD

New research from a 16-week trial conducted by the Physician Committee for Responsible Medicine is adding to the debate around the effectiveness of different dietary approaches.

A randomized, cross-over trial in 62 overweight adult patients, results indicate a low-fat vegan diet appeared to be a more effective approach than adherence to a Mediterranean diet for inducing weight loss and improving cholesterol in this patient population.

"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," said study investigator Hana Kahleova, MD, PhD, director of clinical research for the Physicians Committee, in a statement. "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 trial was conducted between February and October 2019 among a population of adults with a BMI between 28-40 kg/m2. Exclusion criteria for the study included type 1 diabetes, smoking, drug abuse, pregnancy or lactation, and current use of a vegan or Mediterranean diet. All patients included in the trial were randomly assigned in a 1:1 ratio to a Mediterranean diet or low-fat vegan diet for 16 weeks. Following this 16-week period, participants were asked to return to their original diet for 4 weeks and then began the other intervention for 16 weeks.

The primary outcomes of interest included change in body weight, plasma lipids, blood pressure, and body composition. Secondary outcomes in the trial included insulin resistance (HOMA-IR), oral glucose insulin sensitivity (OGIS), and predicted insulin sensitivity (PREDIM) indices.

Upon analysis, investigators found overall weight changes of 0.0 kg for the Mediterranean diet and -6.0 kg with the low-fat vegan diet (treatment effect: -6.0 kg; 95% CI, -7.5 to -4.5; P <.001). When assessing inclusion resistance, HOMA-IR and OGIS increased on the vegan diet and investigators noted no significant changes among those adhering to a Mediterranean diet (treatment effect: -0.7; 95% CI, -1.8 to 0.4; P=.21; and 35.8 mL/min/m2; 95% CI, 13.2 to 58.3; P=.003, respectively). Investigators noted no significant change in PREDIM between either study arms.

In an assessment of patients with no medication changes, results indicated total and LDL-cholesterol decreased 18.7 mg/dL (0.5 mmol/L) and 15.3 mg/dL (0.4 mmol/ L), respectively, on the vegan diet but observed no significant change for either on the Mediterranean diet (t (treatment effect: _15.6; 95% CI, -24.6 to _-6.6; P=.001 and -_14.8; 95% CI, -23.5 to _-6.2; P=.001, respectively). Additionally, systolic and diastolic blood pressure were decreased by 9.3 and 7.3 mmHg on the Mediterranean diet, respectively, compared to reductions of 3.4 and 4.1 mmHg among those on the vegan diet (treatment effect: 5.9; 95% CI, 1.0 to 10.9; P=.02; and -1.8 [95% CI, _-4.6 to 8.1; P=.58, respectively).

"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," added Neal Barnard, MD, study investigator and 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."

This study, “A Mediterranean Diet and Low-Fat Vegan Diet to Improve Body Weight and Cardiometabolic Risk Factors: A Randomized, Cross-over Trial,” was published in the Journal of the American College of Nutrition.