The OMNIVEG Study: Effects of Transitioning from a Traditional to a Vegan Mediterranean Diet on Fat Oxidation During Exercise

Abstract

Background: This study aimed to evaluate the changes in fat utilization associated with transitioning from a traditional to a vegan Mediterranean diet in healthy, physically active men during a ramp exercise test. Methods: In a controlled crossover design, fourteen healthy, physically active men followed a traditional Mediterranean diet for three weeks (baseline). Then, participants transitioned to a four-week isocaloric vegan version of the Mediterranean diet, matched for macronutrient distribution but excluding all animal foods. Immediately after each dietary intervention, participants completed an incremental exercise test (from 30% to 70% of VO2peak) on a cycle ergometer in a fasted state to determine peak fat oxidation (PFO) and its associated exercise intensity (Fatmax). Exercise heart rate and the rating of perceived exertion were also recorded at each exercise intensity. Results: The traditional and vegan Mediterranean diets provided comparable amounts of energy (2599.6 ± 180.8 and 2634.9 ± 148.3 kcal/day, p = 0.140) and total fat (97.0 ± 17.8 and 99.0 ± 13.2 g/day; p = 0.620). However, the vegan Mediterranean diet contained a lower proportion of saturated fat (25.2 ± 6.8 vs. 13.6 ± 4.4% of total fat, p < 0.010). Still, the dietary transition was not associated with modifications in PFO (0.323 ± 0.153 and 0.347 ± 0.147 g/min; p = 0.678) or Fatmax (40.51 ± 7.30 and 40.51 ± 10.71%VO2peak; p = 1.000) during exercise. Moreover, the dietary transition did not significantly change the response curves across exercise intensities for fat oxidation (p = 0.553), heart rate (p = 0.280), or the rating of perceived exertion (p = 0.433). Conclusions: Switching from a traditional to a vegan Mediterranean diet did not affect fat oxidation, exercise intensity at peak fat oxidation, or perceptual responses during exercise in healthy, active men. These findings suggest that physically active individuals can adopt a vegan version of the Mediterranean diet without compromising fat utilization during submaximal aerobic exercise.