A new study from the Physicians Committee for Responsible Medicine has found that a low-fat vegan diet leads to more weight loss than the Mediterranean diet, even when it includes some foods often considered “unhealthy.”
This research, published in Frontiers in Nutrition, looked closely at how different plant-based eating patterns affect weight.
In the study, people on the vegan diet lost more weight than those on the Mediterranean diet. Interestingly, the vegan group still saw results even when eating foods like potatoes and white bread, which some diet systems label as “unhealthy” plant foods.
The key factor in the vegan group’s weight loss was cutting out animal products, including meat, dairy, and fish. These participants also reduced or avoided added oils and nuts, which are usually seen as healthy. Still, this combination seemed to help them lose more weight.
Dr. Hana Kahleova, the lead researcher, explained that avoiding animal products and oils—even while eating some less-than-perfect plant foods—was still more effective for weight loss than following the Mediterranean diet.
The vegan diet included fruits, vegetables, grains, and beans, while the Mediterranean diet also allowed fish, low-fat dairy, and extra-virgin olive oil. Neither group had calorie limits.
In the original study, 62 overweight adults followed one of the diets for 16 weeks, took a four-week break, and then switched to the other diet for another 16 weeks. The first trial showed the vegan diet helped with weight loss, body fat reduction, and improving blood sugar and cholesterol.
In a new analysis of this data, researchers used something called the plant-based diet index (PDI) to explore the quality of the plant-based foods people ate. This index has three scoring systems.
The general PDI score goes up when people eat more plant foods. The hPDI score increases when people eat more fruits, vegetables, whole grains, and nuts. The uPDI score goes up when people eat more “unhealthy” plant foods like white bread, sweet drinks, and potatoes.
The study found that PDI scores went up a lot for those on the vegan diet, but not for those on the Mediterranean diet. The healthy score (hPDI) increased in both groups, while the “unhealthy” score (uPDI) only increased for the vegan group and actually dropped for the Mediterranean group.
Surprisingly, only the increases in PDI and uPDI scores were linked to weight loss—and these only happened on the vegan diet. The hPDI score, which reflects eating more healthy plant foods, did not connect to any weight changes.
So why did the vegan diet work better for weight loss? The answer seems to lie in removing animal products and cutting back on oils and nuts. Even though participants still ate foods like potatoes and white bread, the overall shift to a low-fat, plant-based eating style led to positive changes.
This research shows that moving away from animal-based foods and toward a simple vegan diet—even with a few refined carbs—is a strong strategy for weight control. It also challenges the idea that all plant-based diets must avoid foods like potatoes and bread to be effective.
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