A study published in Frontiers in Nutrition found that a vegan diet led to greater weight loss compared to the Mediterranean diet, even when including foods considered "unhealthy" by some nutritional standards. Overweight adults assigned to the vegan diet experienced more significant reductions in weight, improved body composition, and better insulin sensitivity and cholesterol levels after 16 weeks, without caloric restrictions. The study challenged conventional thinking about plant-based diets and their effectiveness in weight management.

Researchers analyzed the relationship between different types of plant-based foods and weight loss, using a plant-based diet index to categorize foods as "healthful" or "unhealthful." Despite the inclusion of refined grains and potatoes, typically seen as less nutritious, the vegan diet still resulted in better weight loss outcomes than the Mediterranean diet. The study suggests that the exclusion of animal products and reduction in added oils may play a larger role in weight management than solely focusing on consuming healthful plant-based foods.