Table 2 Meta-regression of the efficacy of prebiotics, probiotics and synbiotics on depression

Treatment duration (reference =  > 4 weeks, ≤ 8 weeks)

  ≤ 4 weeks

0.494

0.256

1.93

0.076

-0.059

1.046

  > 8 weeks

0.849

0.419

2.03

0.064

-0.056

1.753

Age

-0.043

0.028

-1.52

0.152

-0.104

0.018

Percentage of females

1.925

0.766

2.51

0.026^*

0.271

3.580

Intervention agent

(Probiotics or non-probiotics)

-0.109

0.231

-0.47

0.643

-0.608

0.389

Intervention type

(Single or adjunctive intervention)

-0.211

0.256

-0.83

0.423

-0.764

0.341

Evaluation timepoint

(After intervention or follow-up)

-0.264

0.241

-1.10

0.292

-0.784

0.256