Vegan Fat Burning

Plant-Powered Endurance: What OMNIVEG Tells Us

The OMNIVEG study involved 14 healthy, physically active young men. They first followed a traditional Mediterranean diet and then changed to a vegan Mediterranean diet for four weeks.

Calories and macronutrients were kept broadly similar: about 48–49% of energy came from carbohydrate and around 34% from fat - both diets.  The Vegan alternative switched the animal foods with legumes, tofu, tempeh, seitan, nuts and fortified plant alternatives, while olive oil remained the main added fat.

Participants then completed a fasted cycling test while researchers measured fat and carbohydrate use in their metabolic process.

Peak fat oxidation averaged:

• 0.323 grams per minute on the traditional Mediterranean diet

• 0.347 grams per minute on the vegan diet

The difference was not statistically significant. Fatmax—the intensity at which fat burning peaked—was identical at about 40.5% of VO₂peak. Heart rate, carbohydrate use and perceived effort were also unchanged.

The appropriate conclusion is therefore:

Replacing animal foods with plant foods, while maintaining similar calorie, carbohydrate and fat intake, did not impair the participants’ ability to use fat during aerobic exercise.

Fatmax is not exactly Zone 2

Fatmax and Zone 2 can overlap, but they are not the same measurement. Fatmax identifies the intensity at which absolute fat oxidation is highest, while Zone 2 is normally defined in relation to the first ventilatory or lactate threshold.

The study also used cycling rather than prolonged running. It involved only 14 men, lasted four weeks and did not include women, older runners or highly trained endurance athletes. Nor did it measure race performance or time to exhaustion.

OMNIVEG therefore provides reassuring preliminary evidence, rather than final proof about every vegan runner’s Zone 2 physiology.

Environmental and cost benefits

A further OMNIVEG analysis published in 2026 examined the environmental impact and retail cost of the two diets. It used the same participants and food records, so it was an extension of the project rather than a new trial.

Compared with the traditional Mediterranean diet, the vegan version was associated with estimated reductions of:

• 54.5% in environmental damage affecting human health

• 50.9% in ecosystem damage

• 43.4% in resource use

These are life-cycle environmental measures covering food production, processing, transport, cooking and waste. The “human health” figure refers to environmental burdens such as pollution, not a 54.5% improvement in the participants’ personal health.

The vegan diet was also calculated to cost 16.3% less at retail. Savings from replacing meat, fish and dairy with legumes and other plant proteins outweighed the extra spending on nuts and plant alternatives.

Prices were based on Madrid, so the exact savings would differ in Britain. Nevertheless, the broader principle is credible: meals based on beans, lentils, chickpeas, whole grains, potatoes and seasonal vegetables can be substantially cheaper than those centred on meat, fish and cheese.

The practical message for runners

Animal foods are not required to preserve the body’s aerobic fat-burning capacity. A well-planned vegan Mediterranean diet maintained normal fuel use during submaximal exercise while also reducing estimated environmental impacts and food costs.

For runners, that is a valuable finding: plant-based eating can support the aerobic engine without compromising performance—and can benefit both the household budget and the planet.

References

López-Moreno M. et al. “The OMNIVEG Study: Effects of Transitioning from a Traditional to a Vegan Mediterranean Diet on Fat Oxidation During Exercise.” Nutrients, 2025.

López-Moreno M. et al. “Environmental and Economic Impact of a Vegan Versus Traditional Mediterranean Diet: OMNIVEG Study.” European Journal of Nutrition, 2026.