Vegan diet delivers more weight loss than Mediterranean, even with refined grains

A new analysis from the Physicians Committee for Responsible Medicine challenges a common assumption: that the "healthiest" plant-based foods are what drive weight loss. The research, published in Frontiers in Nutrition, found that people on a low-fat vegan diet lost more weight than those following a Mediterranean diet—even when their vegan plates included potatoes and refined grains, foods often flagged as less nutritious.

The finding comes from a secondary analysis of a 16-week trial that compared 62 adults with excess weight on two different eating patterns. One group ate a vegan diet of fruits, vegetables, grains, and beans. The other followed a Mediterranean approach with fish, low-fat dairy, and extra-virgin olive oil. Neither group counted calories. After 16 weeks, participants took a break, then switched diets for another 16 weeks.

The vegan group saw greater weight loss, better insulin sensitivity, and improved cholesterol levels. But what made the difference wasn't necessarily eating more kale and quinoa. "Our research shows that even when a low-fat vegan diet includes so-called unhealthy plant-based foods—like refined grains and potatoes—it's better than the Mediterranean diet for weight loss, because it avoids animal products and added oils," says Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee and lead author of the study.

What Actually Drove the Results

When researchers dug into the dietary logs using three different plant-based scoring systems, a clearer picture emerged. The weight loss on the vegan diet correlated most strongly with two things: removing animal products entirely and cutting back on oils and nuts. Eating more whole grains and vegetables mattered, but the removal of animal-based foods was the dominant factor.

This matters because it reframes the conversation. You don't need to eat a "perfect" diet to see results. The vegan group lost weight eating refined grains and potatoes—foods that nutrition guides often warn against—because they were also avoiding the calorie-dense combination of animal products and added fats. The Mediterranean diet, despite its reputation for heart health, includes fish and olive oil, both of which are calorie-rich, even if they're nutritionally valuable.

The research adds to a growing body of evidence showing that for weight management, what you remove from your plate can matter as much as what you add. The mechanism isn't mysterious: animal products and oils are significantly more calorie-dense than whole plant foods. A low-fat vegan diet naturally creates a calorie deficit without the need to count or restrict, which may explain why participants lost weight without being told to eat less.

This doesn't mean the Mediterranean diet is ineffective—it has strong evidence for heart health and longevity. But if weight loss is the specific goal, the data now suggests a low-fat vegan approach edges it out. What happens next will likely depend on individual preferences and whether people can sustain these patterns beyond the study window.