Can a Vegan Diet Boost Weight Loss More Than the Mediterranean Diet? Study Finds Out

A low-fat vegan diet significantly lowers dietary acid load and supports weight loss more effectively than a Mediterranean diet, according to a new randomized crossover trial published in Frontiers in Nutrition.

“Eating acid-producing foods like meat, eggs, and dairy can increase the dietary acid load, or the amount of acids consumed, causing inflammation linked to weight gain,” says Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee and lead author of the study. “But replacing animal products with plant-based foods like leafy greens, berries, and legumes can help promote weight loss and create a healthy gut microbiome.”

The trial included 62 overweight adults who were randomly assigned to follow either a Mediterranean diet or a low-fat vegan diet for 16 weeks. After a four-week washout period, participants switched to the alternate diet for another 16 weeks. Researchers tracked participants’ dietary intake and calculated dietary acid load using two widely accepted indicators, Potential Renal Acid Load (PRAL) and Net Endogenous Acid Production (NEAP). Higher scores reflect a higher acid load, which is linked to inflammation and metabolic disorders.

The results revealed that PRAL and NEAP scores decreased significantly on the vegan diet but remained unchanged on the Mediterranean diet. This reduction in acid load was directly associated with weight loss, independent of changes in calorie intake. Participants lost an average of 13.2 pounds on the vegan diet, while no significant weight change occurred on the Mediterranean diet.

Animal-based foods like meat, fish, eggs, and cheese increase acid production in the body, contributing to chronic inflammation and disrupted metabolism. In contrast, plant-based diets are more alkaline, and have been linked to improved insulin sensitivity, lower blood pressure, and weight reduction.

The researchers suggest that the alkalizing effect of a vegan diet, which raises the body's pH and reduces acidity, could be a key mechanism behind its metabolic benefits.

Reference: Kahleova H, Maracine C, Himmelfarb J, Jayaraman A, Znayenko-Miller T, Holubkov R and Barnard ND (2025) Dietary acid load on the Mediterranean and a vegan diet: a secondary analysis of a randomized, cross-over trial. Front. Nutr. 12:1634215. doi: 10.3389/fnut.2025.1634215