In 2020, Marx et al. published a study in Neuroscience & Biobehavioral Reviews that systematically reviewed 22 randomized controlled trials (RCTs) on 1,551 participants to assess whether probiotic, prebiotic, or fermented food interventions enhanced cognitive performance.

Do Probiotics, Prebiotics, and Fermented Foods Improve Cognitive Function? A Meta-Analysis of Randomized Controlled Trials

Interesting News . Apr 17, 2025

In 2020, Marx et al. published a study in Neuroscience & Biobehavioral Reviews that systematically reviewed 22 randomized controlled trials (RCTs) on 1,551 participants to assess whether probiotic, prebiotic, or fermented food interventions enhanced cognitive performance.

Results and Conclusions

Overall, no significant effects of probiotics, prebiotics, and fermented foods on global cognition were found:
1. Probiotics: (g = 0.115, 95% CI -0.041, 0.270, p = 0.148)
2. Prebiotics: (g = 0.077, 95% CI -0.091, 0.246, p = 0.369)
3. Fermented foods: (g = 0.164, 95% CI -0.017, 0.345, p = 0.076)
While 14 of the 22 individual studies demonstrated improvements in specific cognitive domains, such findings were not consistent across all studies.
Most of the remaining studies (16 of the 22) were rated as low risk of bias, indicating they were somewhat reliable but limited.
The high variability in study designs (specifically regarding differences in participant populations, cognitive tests used, and types of interventions) may account for the lack of significance in the pooled analysis.

What Probiotic and Fermented Foods Were Studied?

If probiotic and fermented foods are considered for cognitive health, here are the most studied sources:

Probiotic strains: The Lactobacillus and Bifidobacterium species are commonly found in yogurt, kefir, and probiotic supplements.
Prebiotics: Fiber-rich foods support gut bacteria and include inulin, galactooligosaccharides (GOS), and fructooligosaccharides (FOS) from bananas, onions, garlic, and asparagus.
Fermented foods: kimchi, sauerkraut, miso, tempeh, kombucha, and fermented dairy (kefir, yogurt, etc.)

Evidence Level: How Strong Is the Science?

A total of 22 randomized controlled trials (RCTs) provides the basis for:

1B: Level of individual studies (high-quality).
Level 1A: Meta-analysis of randomized controlled trials (strongest evidence).

Although meta-analyses of RCTs provide high-level evidence, this study did not demonstrate significant efficacy in improving cognitive performance. It is incredibly difficult to make standard conclusions due to the high variability within populations, study designs, and cognitive tests used.

Final Verdict: Does Science Support It?

About the findings, the recommendations are that probiotics, prebiotics, and fermented foods do not have any definite improvement for global cognition. Some separate studies have indicated that certain domains of cognition may more inure some populations to respond better than others. Further studies will elucidate which cannabis strains, dosages, and duration of treatment will prove to be maximally efficacious.

What Next?

Future research could be concentrated on:

Confirming, using larger, longer-term trials with varied participant populations, general cognitive benefits.
Standardized cognitive tests across studies to enable better comparison.
Examining further the gut-brain axis in terms of probiotics and prebiotics relative to cognition, specifically among certain groups with conditions such as mild cognitive impairment or neurodegenerative diseases.
For personalized approaches to determining who will most benefit from probiotic or fermented-food interventions.

At this juncture, however, given that probiotics and fermented foods have clean roles in gut wellness, they remain uncertain as far as cognitive function is concerned. Meanwhile, nourishing the body with these types of foods would still offer wonderful benefits when integrated into a healthy lifestyle, but they could not be depended on to enhance cognition per se.