Ready to rethink everything you thought you knew about weight loss? A new study published in Frontiers in Nutrition reveals a surprising twist: a vegan diet, even one that includes so-called 'unhealthy' plant-based foods, might be more effective for weight loss than the widely-praised Mediterranean diet. But here's where it gets controversial...
The research, conducted by the Physicians Committee for Responsible Medicine, found that a vegan diet, which naturally emphasizes plant-based foods, led to greater weight loss compared to the Mediterranean diet. The key? Avoiding animal products, and, surprisingly, embracing foods like potatoes and refined grains – those often labeled as 'unhealthy' within the plant-based diet index. Avoiding added oils and nuts, considered 'healthy' by the same index, also contributed to the weight loss.
Hana Kahleova, MD, PhD, and lead author of the study, sums it up: "Our research shows that even when a low-fat vegan diet includes so-called unhealthy plant-based foods... it's better than the Mediterranean diet for weight loss, because it avoids animal products and added oils."
This analysis is a follow-up to a previous study that compared the two diets. In the initial study, 62 overweight adults were randomly assigned to either a low-fat vegan diet (fruits, vegetables, grains, and beans) or a Mediterranean diet (fruits, vegetables, legumes, fish, low-fat dairy, and extra-virgin olive oil) for 16 weeks. Participants then switched diets for another 16 weeks after a 4-week break. The results showed that the vegan diet outperformed the Mediterranean diet in terms of weight loss, body composition, insulin sensitivity, and cholesterol levels.
The secondary analysis dove deeper, examining how the Plant-Based Diet Index (PDI) influenced weight loss on both diets. The PDI assesses diets based on the types of plant foods consumed. It's broken down into three scores:
- PDI: This score goes up with more plant-based foods overall.
- hPDI (healthful PDI): This score increases with more 'healthful' plant-based foods (fruits, vegetables, whole grains, nuts, legumes, oils, coffee, and tea) and fewer 'unhealthful' ones.
- uPDI (unhealthful PDI): This score increases with more 'unhealthful' plant-based foods (fruit juice, sugary drinks, refined grains, potatoes, and sweets) and fewer 'healthful' ones.
The analysis revealed some fascinating insights. The PDI and uPDI scores increased significantly on the vegan diet but remained unchanged on the Mediterranean diet. The hPDI score increased on both diets. The increase in the PDI and uPDI scores on the vegan diet was directly linked to weight loss.
The researchers found that the biggest factor in these score changes was the avoidance of animal products on the vegan diet. Furthermore, reducing the consumption of oils and nuts further boosted the uPDI score.
And this is the part most people miss... These findings suggest that the simple act of swapping animal products for plant-based alternatives, along with limiting oils and nuts, could be a powerful strategy for weight loss.
But here's a thought-provoking question: Could this study challenge the conventional wisdom surrounding 'healthy' eating, especially regarding the role of refined grains and potatoes? Do you think the focus on avoiding animal products is the primary driver of weight loss in this case, or are other factors at play? Share your thoughts in the comments below!
Source: Kahleova, H., et al. (2025). Plant-based dietary index on the Mediterranean and a vegan diet: a secondary analysis of a randomized, cross-over trial. Frontiers in Nutrition. doi: 10.3389/fnut.2025.1666807.
