Vegan Diet Promotes Greater Weight Loss than Mediterranean Diet in Adults — Evidence Review
Published in Frontiers in Nutrition, by researchers from Physicians Committee for Responsible Medicine
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Table of Contents
A new analysis found that a low-fat vegan diet resulted in greater weight loss than the Mediterranean diet, even when including "unhealthy" plant-based foods like refined grains and potatoes. These results, published in Frontiers in Nutrition, align with most prior research showing vegan diets often produce more weight loss than other dietary patterns. Related studies largely support these findings, though some highlight differences in long-term sustainability and health outcomes between vegan and Mediterranean diets.
- Several randomized controlled trials and meta-analyses have shown that vegan and vegetarian diets generally lead to more weight loss than omnivorous or Mediterranean diets, especially when energy intake is not restricted, supporting the new study’s conclusions 2 3 4.
- Mediterranean diets are also effective for weight loss and improve cardiovascular and metabolic risk factors, but may yield slightly less weight loss compared to vegan diets in direct comparisons, although results can depend on diet composition and adherence 6 7 10.
- Evidence suggests that increasing the proportion of plant-based foods in both vegan and Mediterranean diets can further enhance health benefits, and both patterns are associated with lower BMI and healthier lifestyle habits 4 12 13 14.
Study Overview and Key Findings
Growing interest in plant-based and Mediterranean diets has prompted researchers to directly compare their impacts on weight management and metabolic health. This new analysis is notable because it examines not only overall dietary patterns, but also how the inclusion of foods labeled as "unhealthy" on plant-based diet indices—such as refined grains and potatoes—affects weight loss outcomes. The findings offer insights into the relative roles of animal product exclusion and specific plant-based food choices in promoting weight loss.
| Property | Value |
|---|---|
| Organization | Physicians Committee for Responsible Medicine |
| Journal Name | Frontiers in Nutrition |
| Authors | Hana Kahleova, MD, PhD |
| Population | Adults with excess weight |
| Sample Size | 62 adults |
| Methods | Randomized Controlled Trial (RCT) |
| Outcome | Weight loss, body composition, insulin sensitivity, cholesterol levels |
| Results | Vegan diet led to greater weight loss than Mediterranean diet. |
In this secondary analysis, participants followed either a low-fat vegan or Mediterranean diet, each for 16 weeks, with cross-over after a four-week break. The vegan diet encouraged fruits, vegetables, grains, and beans, while the Mediterranean diet included fish, dairy, and olive oil. No calorie restriction was imposed. Weight loss was greater on the vegan diet, and this effect was linked to increased intake of a broad range of plant-based foods—including some labeled "unhealthy" by the plant-based diet index—along with limitation of animal products, oils, and nuts.
Literature Review: Related Studies
To contextualize these findings, we searched the Consensus paper database, which contains over 200 million research papers, using the following queries:
- vegan diet weight loss comparison
- Mediterranean diet effectiveness for weight loss
- plant-based diet health outcomes versus Mediterranean
The following table summarizes key topics and findings from related studies:
| Topic | Key Findings |
|---|---|
| How do vegan and vegetarian diets compare to Mediterranean and other diets for weight loss? | - Vegan diets consistently lead to greater weight loss than vegetarian, pesco-vegetarian, Mediterranean, and omnivorous diets in RCTs and meta-analyses 2 3 4. - Mediterranean diets produce moderate weight loss, especially when energy-restricted, but may result in less reduction than vegan diets in direct comparisons 6 7 10. |
| Does the quality and composition of plant-based diets influence health and weight outcomes? | - Vegan diets high in whole plant foods and low in oils or nuts can enhance weight loss and cardiometabolic benefits 1 2 4 12. - Higher intake of refined grains and potatoes (often considered "unhealthy" in plant-based indices) may not negate weight loss benefits when animal products and added fats are limited 1 4. |
| What are the long-term effects and sustainability of vegan and Mediterranean diets? | - Both diets are associated with sustained weight loss and improved metabolic health, but long-term studies indicate greater adherence and potential health advantages with Mediterranean diets in some populations 3 7 10 13. - Vegan diets may carry a higher risk of dropout or disordered eating in some groups 5 13. |
| How do these diets affect cardiovascular and metabolic risk factors? | - Both vegan and Mediterranean diets lower cholesterol and improve glycemic control, with vegan diets showing larger reductions in LDL cholesterol and weight in some trials 1 4 8 9 12. - Mediterranean diets provide cardiovascular benefits, especially when combined with physical activity and energy restriction 6 7 8 9. |
How do vegan and vegetarian diets compare to Mediterranean and other diets for weight loss?
The related studies overwhelmingly find that vegan diets are associated with greater weight loss than Mediterranean, vegetarian, or omnivorous diets, particularly in randomized controlled trials where energy intake is not specifically restricted. The new study's findings are consistent with this pattern and provide further evidence that exclusion of animal products plays a significant role in weight loss, even when the plant-based diet includes foods sometimes labeled as "unhealthy" 2 3 4 6.
- Vegan diets promoted greater weight loss than omnivorous, semi-vegetarian, and Mediterranean diets in several RCTs, with weight reductions ranging from 2.5 to 7.5% over 6 to 18 months 2 3 4.
- Mediterranean diets also led to significant weight loss, particularly when energy-restricted or combined with physical activity, but typically produced somewhat less weight reduction than vegan diets in direct comparisons 6 7 10.
- The observed differences in weight loss may be explained by the lower energy density and higher fiber content of vegan diets, as well as the exclusion of calorie-dense animal products 2 4.
- Adherence and support (e.g., group meetings) can influence the magnitude and sustainability of weight loss across all dietary patterns 3.
Does the quality and composition of plant-based diets influence health and weight outcomes?
Studies indicate that while the overall shift to a plant-based diet is beneficial for weight loss and metabolic health, the quality of plant foods consumed also plays a role. However, the exclusion of animal products appears to be a primary driver of weight loss, even when refined grains or potatoes are included, as shown in the new analysis 1 2 4 12.
- Vegan diets that emphasize whole, minimally processed foods (fruits, vegetables, whole grains, legumes) are associated with greater reductions in body weight and cardiovascular risk factors 1 2 4 12.
- The plant-based diet index categorizes some plant foods as "unhealthy" (e.g., refined grains, potatoes), but their consumption did not prevent weight loss in the context of a low-fat vegan diet 1 4.
- Limiting added oils and nuts, which are calorie-dense, may further enhance weight loss in plant-based diets 1 2.
- Increased dietary fiber and lower energy density are important contributors to the observed health benefits of plant-based patterns 4 12.
What are the long-term effects and sustainability of vegan and Mediterranean diets?
While both vegan and Mediterranean diets demonstrate health benefits and weight loss in the short to medium term, evidence regarding long-term adherence and outcomes is mixed. Some studies suggest better adherence to Mediterranean patterns, while vegan diets may present challenges for some individuals over longer periods 3 7 10 13.
- Long-term randomized trials show sustained weight loss with both diets, though Mediterranean diets may be easier to maintain for many people due to broader food choices and cultural acceptance 3 7 10.
- Vegan diets have been associated with higher rates of attrition or dropout in some studies, often due to dietary restrictions or social factors 5 13.
- Both patterns are linked to healthier lifestyle behaviors, but individuals following vegan diets may need professional guidance to prevent potential nutritional deficiencies or disordered eating patterns 13.
- The environmental and public health impact of both diets is favorable, with vegan diets offering additional sustainability benefits 14 15.
How do these diets affect cardiovascular and metabolic risk factors?
A substantial body of evidence shows that both vegan and Mediterranean diets improve lipid profiles, glycemic control, and other cardiometabolic risk factors. The magnitude and specific profile of these effects may differ between the two dietary patterns 1 4 8 9 12.
- Vegan diets have demonstrated greater reductions in LDL cholesterol and weight, which may translate into lower cardiovascular risk 1 4 12.
- Mediterranean diets also lower cholesterol and improve glycemic control, particularly in people with type 2 diabetes or metabolic syndrome 6 7 8 9.
- Both diets have favorable effects on blood pressure, inflammation, and other cardiovascular markers, especially when combined with energy restriction or increased physical activity 7 8 9.
- The inclusion of more whole plant foods within the Mediterranean diet may further amplify its health benefits 14.
Future Research Questions
Although the evidence base for vegan and Mediterranean diets is robust, important questions remain regarding their long-term effects, optimal composition, and impact across different populations. Further research is needed to clarify these issues and guide dietary recommendations.
| Research Question | Relevance |
|---|---|
| What are the long-term health effects and adherence rates of low-fat vegan versus Mediterranean diets? | Understanding sustainability, health outcomes, and real-world adherence over several years is crucial for informing dietary guidelines and public health policy 3 7 10 13. |
| How do different types of plant-based foods (e.g., refined vs whole grains) impact weight loss and metabolic health on vegan diets? | More research is needed to determine whether including "unhealthy" plant foods in vegan diets affects long-term health outcomes, beyond short-term weight loss 1 4 12. |
| Do energy-restricted vegan and Mediterranean diets produce similar weight loss and cardiometabolic benefits in diverse populations? | Direct comparisons with controlled energy intake and across various age, ethnic, and health groups are limited and could clarify optimal dietary strategies 4 6 7 9 10. |
| What are the psychosocial and behavioral factors influencing adherence to vegan and Mediterranean diets? | Identifying barriers and facilitators to long-term adherence can help tailor interventions and support for different populations 3 5 13. |
| How do plant-based and Mediterranean diets affect health outcomes in patients with chronic diseases such as diabetes or cardiovascular disease? | While both diets show benefits in metabolic health, further studies are needed in populations with existing chronic conditions to optimize recommendations 1 4 8 9 12. |
This comprehensive analysis indicates that while both low-fat vegan and Mediterranean diets have demonstrated efficacy for weight loss and metabolic improvements, vegan diets may offer a modest advantage in short-term weight reduction—even when including some processed plant foods—primarily due to the exclusion of animal products and added fats. However, long-term adherence, nutritional adequacy, and individualization remain important considerations for future research and clinical practice.