Better gut health reduces depression and anxiety across 70 randomized controlled trials
STUDY: Lian J et al, Ann Gen Psychiatry. 2026 Apr 20
STUDY TYPE: Systematic review and meta-analysis of randomized controlled trials
FUNDING: Independent
Background
Gut microbiota influence serotonin production, inflammatory pathways, and the stress hormone system. There are three supplements that improve gut health, and this analysis looked at their effects on anxiety and depression:
- Prebiotics: The fibrous foods that probiotics thrive on
- Probiotics: Healthy gut bacteria, the more diverse the better
- Synbiotics: A combination of probiotics and prebiotics
The Study
Researchers pooled 70 randomized controlled trials — 65 for depression and 49 for anxiety — comparing pre-, pro-, or synbiotics against placebo in adults. Studies ranged from 2 to 24 weeks.
- Pre- and probiotics reduced depressive symptoms with a moderate effect (SMD 0.57) that was greater in clinical depression (0.63) and in adults over 50 (0.68).
- Probiotics and synbiotics both worked for depression; prebiotics alone did not.
- All three types reduced anxiety, with synbiotics showing the strongest effect.
Limitations: Heterogeneity across studies was high (I² >80%), and publication bias was detected for depression — the true effect size is likely smaller than reported.
Practice Implications
- It’s tempting to think these are just for mild cases, but the evidence suggests they work better with more significant symptoms.
- On my supplements page I’ve listed low-cost synbiotics that were tested by independent labs and contain the strains used in these trials.
— Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
