A randomized clinical trial adds new evidence to the growing conversation around how diet choices affect both personal health and environmental impact.
In a secondary analysis published in BMJ Nutrition, Prevention & Health, researchers found that overweight adults following a low-fat vegan diet for 16 weeks reduced food-related greenhouse gas emissions by 57%. During a Mediterranean diet phase, emissions fell by 20%. Participants on the vegan diet also saw greater short-term improvements in weight, insulin sensitivity and cholesterol levels.
The study was conducted and funded by the Physicians Committee for Responsible Medicine, a nonprofit organization that promotes plant-based diets. According to the authors, the funding source was not involved in the study’s design, data collection, analysis, interpretation, manuscript preparation or publication decision. Still, because the organization has a clear advocacy position, that context is worth considering alongside the study’s methodology and findings.
The trial included 62 adults in a randomized crossover design, meaning participants followed both diets during separate phases. Researchers matched detailed food records with environmental databases to estimate each diet’s greenhouse gas emissions and energy demand.
Much of the environmental difference came from removing animal products, particularly meat and dairy, which generally produce more emissions than plant foods.
Still, the findings do not mean all vegan diets are automatically healthier or more sustainable than all Mediterranean diets.
This study specifically examined a low-fat vegan diet centered on foods such as vegetables, grains and legumes. Mediterranean diets can also vary widely depending on how much fish, dairy, poultry or red meat a person includes.
That distinction matters because food quality, sourcing and long-term adherence all shape both health outcomes and environmental impact.
The trial was relatively small and lasted 16 weeks per diet phase. While randomized trials typically offer stronger evidence than observational studies, this design cannot determine whether one eating pattern is universally superior or easier to sustain over time.
Rather than treating this as a simple vegan-versus-Mediterranean verdict, the findings may be most useful as part of a larger conversation about how dietary patterns influence both human health and planetary resources.