[Clinical evidence on kefir consumption and human health]

Introduction: kefir is a fermented drink rich in bioactive metabolites and microorganisms with potential as a functional food. Emerging evidence suggests positive effects on metabolism, gut microbiota, inflammation and the gut-brain axis, although its clinical relevance has not yet been clearly established. Objective: to synthesise the existing clinical evidence on how kefir consumption affects human health, including metabolic, gastrointestinal, immunological, cognitive and physical performance aspects. Methods: narrative review of human clinical studies, randomised controlled trials and meta-analyses evaluating kefir consumption in different population groups. Results relating to metabolic markers, inflammation, cognitive function, physical activity, gut health and safety were analysed. Results: kefir consumption is consistently associated with increased insulin sensitivity and a slight reduction in fasting glucose levels. The effects on lipid profile, blood pressure and systemic inflammation are mixed. A modulation of the gut microbiota is observed, with an increase in beneficial bacteria and improved intestinal permeability. The evidence regarding brain health is preliminary, with some indications of cognitive improvement and enhanced well-being. Potential benefits in physical performance and recovery have also been reported. Kefir has a favourable safety profile, with mild and transient adverse effects. Conclusions: kefir has modest but promising beneficial effects in various areas of health, particularly in metabolism and gut function. However, methodological heterogeneity and the limited quality of the studies prevent firm conclusions from being drawn. Robust, standardised clinical trials are required to define its efficacy and clinical applicability.