Real-World Fermented Foods and Their Impact on Gut and Brain Health: A Multi-Arm Intervention Study in Healthy Adults

Fermented foods are increasingly recognized for their potential to support gut and brain health via microbiome modulation. However, most research focuses on isolated probiotics or lab-prepared products, leaving limited evidence for real-world fermented foods with live bacteria. This study evaluated the effects of three commercially available fermented foods—dairy kefir, coconut kefir, and fermented red cabbage and beetroot—on gastrointestinal, cognitive, and emotional outcomes in healthy adults. Over a 4-week randomized controlled intervention, cognitive function was assessed using the CANTAB, emotional health via validated self-report measures, and stool samples analysed using the Genova Diagnostics GI Effects test. Dairy kefir improved decision-making, sustained attention, working memory, reduced depression, anxiety and stress. The coconut kefir reduced waiting impulsivity, enhanced short-term memory, improved total mood, and increased butyrate-associated commensals, Faecalibacterium prausnitzii, Bifidobacterium spp., Lactobacillus spp., and Anaerotruncus colihominis, alongside elevated butyrate levels. The fermented red cabbage and beetroot improved sustained attention, working memory, reduced stress, improved total mood, and increased both butyrate and propionate. In contrast, the control group showed a rise in Fusobacterium spp. These findings support fermented foods as functional dietary interventions for gut–brain health.