The Gut–Brain Axis and Probiotics in Beverages and Liquid Preparations: A PRISMA Systematic Review on Cognitive Function Enhancement

The gut–brain axis links the health of the gut microbiota to cognitive function and mental well-being. Numerous studies suggest that probiotics, particularly strains belonging to Lactobacillus spp. and Bifidobacterium spp., can positively modulate memory, attention, and executive functions, contributing to the prevention of cognitive decline. However, while the use of probiotic capsules and powders is widely documented, the role of probiotic beverages or liquid preparations in brain health remains poorly explored. This systematic review analyzes studies on the efficacy of probiotics in improving cognitive functions from 2020 to 2025, evaluating the potential of probiotic liquid preparations as a delivery vehicle. The results indicate that fermented beverages or liquid suspensions containing probiotics could improve the bioavailability of beneficial microorganisms, promoting synergistic effects with other bioactive components and facilitating treatment adherence. However, the current literature still has methodological limitations and there is a need for further clinical studies to validate the efficacy of this strategy. Probiotic supplementation through functional beverages could represent a promising innovation to improve cognitive health and counteract neurocognitive decline.