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Field notes

Diet patterns

Field note Vegan People who eat no animal foods, compared with vegetarians and omnivores. Seen again and again Field note Vegetarian People who eat no meat or fish, compared with vegans and omnivores. Seen again and again Field note Omnivore People who eat both plant and animal foods, compared with vegetarians and vegans. Seen again and again

The microbes, diet by diet

Landmark study

21,561 people in 5 cohorts, by the diet they said they follow: 19,817 omnivores, 1,088 vegetarians and 656 vegans (Fackelmann 2025). Comparing omnivores with vegetarians, 13 of our microbes are higher in omnivores, and 6 in vegetarians; 203 more show very small differences.

An association the authors report, measured once per person. It doesn’t mean a diet changes this microbe, or that the microbe affects health.

Phylum

Higher in omnivores 11

Biggest difference first · omnivores vs vegetarians
  1. Odoribacter splanchnicus Higher in 5 of 5 cohorts
  2. Bilophila wadsworthia Higher in 5 of 5 cohorts
  3. [Ruminococcus] torques Higher in 5 of 5 cohorts
  4. Alistipes putredinis Higher in 5 of 5 cohorts
  5. Butyricimonas paravirosa Higher in 5 of 5 cohorts

Higher in vegetarians 5

Biggest difference first · omnivores vs vegetarians
  1. Dialister hominis Higher in 5 of 5 cohorts
  2. Thomasclavelia saccharogumia Higher in 5 of 5 cohorts
  3. Bifidobacterium longum Higher in 4 of 5 cohorts
  4. Bifidobacterium catenulatum Higher in 4 of 5 cohorts
  5. Bacteroides reticulotermitis Higher in 2 of 2 cohorts

1,062 more of our microbes were compared with no clear difference, or only in one cohort.

“Higher” is the study’s measure: on average, a bigger share of gut bacteria across everyone in the group, carriers or not. It isn’t how many people carry it.

Only results the authors call clear (q under 0.1) that come from at least 2 of the 5 cohorts. Differences under the usual size for a small one (a standardized difference under 0.2) don't lead the lists: they're folded, labeled. Their table lists 3,480 microbes for this pair; 1,294 of the 1,557 with a species name across the study are microbes we list, and the rest have no page here.

Fackelmann G et al., Nature Microbiology 2025, CC BY 4.0 · Supplementary Table 10 · About the study · Data sources