Vegan Versus Mediterranean for Person and Planet: New Clinical Trial

As a dietitian, I’ve always supported a plant-based approach to eating. Increasing plants, reducing ultra-processed foods, and being mindful of our environmental impact are all incredibly important. But I’ll be honest—I’ve never routinely recommended a fully vegan diet for most people. One of the greatest skills of dietitians is the ability to see the extremely complex web that is nutrition: life is not like a clinical trial and in order to succeed sustainably, we have to think of all parameters. If I have to start with a summary - I don't believe the vegan diet is a safe option for the long term for most people. That doesn't mean I can't appreciate science though. And it also doesn't mean that I don't appreciate diets heavy in plants - I absolutely do!

A recent clinical trial (Environmental footprint of a low-fat vegan diet and Mediterranean diet: a secondary analysis of a randomised clinical trial in BMJ Nutrition Prevention and Health), and its environmental analysis, has brought this conversation back into focus in a meaningful way.

This was a well-designed randomised crossover clinical trial involving 62 adults, where participants followed a low-fat vegan diet, excluding all animal products and added fats such as oils, nuts and seeds, and a Mediterranean diet including fish, dairy and olive oil. Each diet was followed for 16 weeks, with participants switching diets after a washout period.

A secondary analysis looked not only at health outcomes but also at environmental impact, measured through greenhouse gas emissions and cumulative energy demand. As someone with a degree in Environmental Biogeoscience, this intersection between nutrition and planetary health is particularly important to me, as food is one of the most powerful drivers of environmental change.

The results were striking. The low-fat vegan diet reduced greenhouse gas emissions by 57% and reduced energy demand by 55%. The Mediterranean diet also reduced emissions, but only by 20%, and showed no significant change in energy demand. The primary driver of this difference was the reduction in animal-based foods, particularly meat and dairy, which are known to contribute disproportionately to global emissions.

Although this particular paper focused on environmental outcomes, the same trial also showed that the vegan diet led to greater weight loss and improvements in metabolic health markers such as insulin sensitivity and lipid profiles. In a controlled setting, the vegan diet appeared to outperform the Mediterranean diet in several areas.

However, this is where nuance becomes essential. A low-fat vegan diet within a clinical trial is very different from what most people can realistically achieve, or feel well with, in everyday life. In practice, meeting adequate protein requirements on a vegan diet can be challenging without careful planning. A higher fibre intake can also exacerbate gastrointestinal symptoms in many individuals, particularly those with existing sensitivities. In addition, maintaining a well-balanced vegan diet requires time, knowledge and consistency, which can be difficult in a busy society where many households have two working parents and limited time for meal preparation. It is anecdotal, but after twenty years of clinical practice, I cannot say that the vegans I encounter are healthier than the people who eat a great deal of plant based food with animal products featuring more modestly.

For these reasons, I do not interpret this study as evidence that everyone should adopt a fully vegan diet. Instead, it reinforces a more practical and powerful message: the more we move towards plant-based eating, the better it is for both our health and the environment. Learn to cook beans!

A more realistic approach for most people is to aim for a predominantly plant-based diet, increasing intake of legumes, whole grains, vegetables, nuts and seeds where tolerated, while reducing rather than completely eliminating animal products. This approach is more sustainable in the long term and more achievable for the majority of people. For example, aim for one meal a day with plenty of plant based protein and your other meals with lots of plant foods accompanied by 100g of animal protein.

What this study also highlights is the need for better nutrition education. If more people were taught how to build balanced plant-based meals, meet protein requirements, support gut health while increasing fibre, and integrate these habits into a busy lifestyle, the impact could be significant. Without this knowledge, even the most evidence-based dietary approaches can feel overwhelming and difficult to maintain.

This study ultimately supports the idea that dietary change does not need to be extreme to be meaningful. Vegan diets can offer substantial benefits, and Mediterranean diets remain well-supported for long-term health. However, the greatest opportunity lies in helping people move along the spectrum towards more plant-based eating while not missing out on nutrient dense animal based foods that uniquely provide vital nutrients like vitamin B12.

You do not need to follow a strictly vegan diet to make a meaningful difference. Small, consistent shifts towards a more plant-focused way of eating can have a significant impact on both individual health and the health of the planet. Remember: nutrition science transferred into behaviour requires nuance and personalisation: your dietitian will do that for you - you are unique and deserve to be treated as such!