Wirnitzer et al. 2022, NURMI study of vegan and omnivorous runners

Large cross-sectional cohort of endurance runners by diet type. Any differences in race times between vegan, vegetarian and omnivorous runners are confounded by training behaviour, experience and body mass, and do not establish a causal effect of diet on performance; the authors caution against reading the comparison as causal. Limited (cross-sectional, self-reported, confounded).