Pooling 27 randomised trials, probiotics showed no significant effect on depressive symptoms over short (under 6 weeks) or medium (6-12 weeks) durations, with a significant benefit appearing only in a long-duration subgroup of just 2 studies. Prebiotics and postbiotics showed no clear effects.
What it shows: Systematic review and meta-analysis of 27 RCTs published 2016-2024, but the only significant signal rests on 2 long-duration trials; substantial heterogeneity across studies and overall certainty rated moderate for inconsistency.Review · Nutr Neurosci