What did the researchers do?
The study integrated stool metagenomes and diet information from 21,561 people in five international cohorts, comparing omnivore, vegetarian and vegan patterns. Testing across multiple cohorts was a major strength.
What was found?
Microbial profiles distinguished dietary patterns with reasonably high accuracy, supporting a robust diet-microbiome association. But the result was not simply “vegans have more microbial species”; richness varied by cohort and dietary composition.
Some microbes characteristic of vegan diets correlated with favorable cardiometabolic markers and were also enriched in omnivores who ate more plant foods. This suggests the quality and inclusion of plant foods may matter beyond the diet label.
Diversity is not a simple score
Microbial diversity is useful, but a higher number alone does not define health. Which organisms are present, what they do, the host’s health and the overall diet all matter. This study examined composition and function, not just one diversity score.
Important limitations
The data were mainly cross-sectional and observational, not a trial assigning diets. Self-reported diet, country and social context, and duration of dietary patterns leave residual uncertainty. The study cannot conclude that one diet is best for everyone.
A careful practical takeaway
The study does not require everyone to eliminate animal foods. A practical interpretation is to add more minimally processed plant foods—beans, greens, roots, mushrooms, whole grains, nuts and seeds—within your current pattern.