Fig. 4
From: Effect of prebiotics, probiotics, synbiotics on depression: results from a meta-analysis
a based on whether prebiotics, probiotics and synbiotics were used as adjunctive therapy, b based on different intervention duration (i.e., ≤ 4 weeks, 4 to 8 weeks and > 8 weeks), c based on whether the assessment of depression was performed at the end of the intervention or after a follow-up period, d based on the different assessment tools of depressive symptom (HDRS or BDI)