Antioxidant Provision of Vegan and Vegetarian Versus Omnivorous Diets in Apparently Healthy Humans: A Systematic Review

Dietary antioxidant intake, circulating antioxidant status, and oxidative damage are distinct constructs, yet “antioxidant provision” is treated as a single quantity. This systematic review without meta-analysis (PRISMA 2020, SWiM; INPLASY202670020) asked whether vegan and vegetarian diets differ from omnivorous diets in apparently healthy humans. Three search rounds covered eight sources; because assays could not be harmonized, direction of effect was vote-counted and presented as descriptive evidence maps, with exact binomial p-values reported for transparency, not as evidence of benefit. We included 124 reports of 99 participant samples from 35 countries. Intake favored the plant-based pattern in 18 of 27 informative comparisons (p = 0.12), circulating status in 10 of 18 (p = 0.81), and oxidative damage in 10 of 12 (p = 0.039); one further comparison would overturn the damage result. In the full-text-restricted analysis (the 50 studies read in full by both coders), no family differed from chance. The only robust finding is a substitution: higher vitamin C and vitamin E, lower selenium and zinc; higher copper, carotenoids, and manganese were weaker. Certainty was very low. Because Scopus, Web of Science, Embase, CENTRAL, LILACS, and SciELO were not searched, the search is partial and the counts provisional.