Can psychobiotics “mood” ify gut? An update systematic review of randomized controlled trials in healthy and clinical subjects, on anti-depressant effects of probiotics, prebiotics, and synbiotics

Depression is a major debilitating health problem with high global prevalence. Gut microbiota dysbiosis might be implicated in pathophysiology of depression. Hence, probiotics, prebiotics and synbiotics (psychobiotics) have been administered in clinical trials in attempt to relieve depressive symptoms. This update systematic review aimed to evaluate the current body of research concerning the effects of psychobiotics on depression. PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines were followed in this review. Search was performed in MEDLINE, ProQuest, EMBASE, PsycNET, and Scopus databases for randomized clinical trials which assessed the effects of psychobiotics on depressive symptoms among adults, and were published in English language, since inception until September 2018. Out of 3374 records screened, 32 articles met the study criteria; only seven studies reported significant anti-depressant effects of psychobiotics. Some probiotic strains showed beneficial effects on depressive symptoms; the results were inconsistent, though. Few studies investigated the effects of prebiotics or synbiotics on depression, and did not come up with much promising results The overall risk of bias was judged to be unclear across the included studies, and major confounding factors were not considered in their design. Since probiotics may affect depression in strain-specific manner, the current evidence is not sufficient to either support or decline anti-depressant effects of probiotics; results of studies on prebiotics and synbiotics are not conclusive, either. More well-designed studies with emphasis on specific probiotic strains, inter-individual gut microbiota variations, and depression subtypes are warranted. CRD42018107356.