Prebiotics, probiotics, fermented foods and cognitive outcomes: A meta-analysis of randomized controlled trials.

This systematic review and meta-analysis aimed to evaluate randomized controlled trials that investigated the use of probiotic, prebiotic, and fermented food interventions for cognitive performance. In total, 22 studies (n = 1551) were included that investigated probiotics (11 studies, n = 724), prebiotics (5 studies, n = 355), and fermented foods (6 studies, n = 472). Despite several individual studies (14 of 22) reporting significant improvements in specific cognitive domains, results of the pooled meta-analysis found no significant effect for any intervention for global cognition (Probiotics: g = 0.115, 95 %CI -0.041, 0.270, p = 0.148; Prebiotics: g = 0.077, 95 %CI -0.091, 0.246, p = 0.369; Fermented food: g = 0.164 95 %CI -0.017, 0.345, p = 0.076) or any individual cognitive domain. Most studies (16 of 22) had low risk of bias. These results do not support the use of probiotic, prebiotic, and fermented food interventions for cognitive outcomes. This may be due to the limited number of small and short-term studies as well clinical heterogeneity relating to the population, cognitive tests, and intervention. Therefore, further trials that investigate these interventions in clinical populations using adequately powered samples are warranted. PROSPERO: CRD42019137936.