Low-Fat Vegan Diet Leads to Greater Weight Loss Than the Mediterranean Diet, Study Finds

• Nutrition

In a new analysis published in Frontiers in Nutrition, researchers found that a low-fat vegan diet can lead to greater weight loss than the traditional Mediterranean diet, even when it includes foods that some nutritional indexes consider “less healthy,” such as potatoes or refined grains.

This finding challenges some common beliefs about strict nutritional quality and highlights the importance of replacing animal-based products with plant-based foods as an effective strategy for managing body weight.

What exactly did the study compare?

The research was based on a randomized crossover trial in which 62 overweight adults followed two dietary patterns for 16-week periods: a low-fat vegan diet and a traditional Mediterranean diet. Between both phases, there was a 4-week washout period during which participants returned to their usual eating habits before switching diets.

• In the vegan diet, participants consumed fruits, vegetables, grains, and legumes, completely excluding animal products and reducing oils and nuts.

• The Mediterranean diet was based on fruits, vegetables, legumes, fish, low-fat dairy, and extra virgin olive oil as the main fat source.
  No calorie limits were imposed in either dietary plan.

Key results: greater weight loss with a vegan diet

Although both diets provided metabolic health benefits, participants following the vegan diet lost more weight on average than those on the Mediterranean diet and experienced improvements in:

• Body composition, with a significant reduction in body fat.

• Insulin sensitivity, a key factor in preventing type 2 diabetes.

• Cholesterol levels, with reductions that support cardiovascular health.

These results suggest that, beyond the perceived “healthiness” of individual foods, simply eliminating animal products and limiting added fats may be particularly effective for weight loss.

The role of the Plant-Based Diet Index

An interesting aspect of the analysis was the use of the Plant-Based Diet Index (PDI), a tool that categorizes plant foods as “healthy” or “unhealthy” based on nutritional quality.

• “Healthy”: fruits, vegetables, whole grains, legumes, nuts, healthy oils.

• “Unhealthy”: fruit juices, sugary drinks, refined grains, potatoes, sweets.

Researchers observed that, in the vegan group, not only did overall plant food intake (PDI) increase, but the score for “unhealthy” plant foods (uPDI) also rose as participants replaced animal products with options such as potatoes or white bread. Despite this, the increase was still associated with greater weight loss. In contrast, in the Mediterranean diet group, “unhealthy” scores decreased but did not result in comparable weight reduction.

Why did the vegan diet work better?

Experts point to several possible explanations:

1. Lower overall calorie density: Even when some vegan foods are considered “less healthy,” they tend to have fewer calories per volume than animal-based foods and oils.

2. Higher fiber content: Plant foods are rich in fiber, promoting long-lasting satiety and appetite regulation.

3. Reduced saturated fat and cholesterol: Eliminating animal products lowers saturated fat intake, which may influence metabolic efficiency.

4. Combined effects of multiple plant foods: Replacing several animal energy sources with plants and grains may affect metabolic mechanisms beyond calorie count alone.

Does this mean everyone should go vegan?

While the results are promising, they do not necessarily mean that a vegan diet is superior in all contexts or for everyone. Food quality, individual nutritional needs, and personal preferences remain essential factors for long-term health and sustainability.

Additionally, the study did not focus on environmental or social aspects. However, previous research has shown that plant-based diets are generally associated with lower greenhouse gas emissions and a smaller ecological footprint compared to diets high in animal products.

Conclusion: putting plant foods first

The research suggests that a low-fat, well-designed vegan diet can be an effective strategy for weight loss, even when it includes plant foods not considered “highly healthy.” This opens the door to more flexible plant-based approaches that do not rely solely on premium or highly processed foods, but instead focus on simplicity and replacing animal products.

For those seeking to lose weight sustainably and improve metabolic health without strict calorie counting, this vegan approach may offer a valuable alternative to traditional diets such as the Mediterranean diet. As always, consulting healthcare professionals before making significant dietary changes is recommended.