Stool pooled from 3 severely depressed men, given to antibiotic-depleted rats, produced anhedonia (p=0.022) and anxiety-like behavior (p=0.029).
Ten years on, the largest human trial, n=60, missed its primary endpoint.
Scientists transferred gut bacteria from depressed people to rats.
The rats then developed behaviors characteristic of depression (anhedonia and anxiety-like behavior).
Sep 24, 2026 · 8:00 PM UTC
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Kelly et al., Transferring the blues: Depression-associated gut microbiota induces neurobehavioural changes in the rat, Journal of Psychiatric Research 2016, APC Microbiome Institute, University College Cork (28 rats, 13 given depressed-donor microbiota; the human trial is Li et al., Cell Host and Microbe, July 2026, remission 43.3% vs 26.7%, p=0.176).
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