Sustainable next-generation prebiotics for brain health: microbiota–gut–brain axis in neurodegenerative and demyelinating diseases

Neurodegenerative and neuroinflammatory diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis, are increasingly associated with disruption of the microbiota-gut-brain axis. Common alterations include reduced beneficial microbial taxa, impaired short-chain fatty acid production, intestinal and blood-brain barrier dysfunction, and sustained inflammatory responses. These findings support the development of microbiota-targeted dietary interventions. This review summarizes current evidence on polyphenols, bioactive peptides, and pectin-derived oligosaccharides (POS) as prebiotic or prebiotic-like compounds with potential activity through the microbiota-gut-brain axis. Particular attention is given to structure-function relationships, host-microbe interactions, and the sustainable recovery of these compounds from food by-products. Preclinical studies suggest that these bioactives may reduce microglial activation, improve mitochondrial function, strengthen intestinal and blood-brain barrier integrity, and enhance cognitive or motor performance. Early clinical studies also indicate possible benefits on mood, selected cognitive outcomes, metabolic regulation, and inflammatory biomarkers, although evidence remains limited. Microbiota-derived metabolites from polyphenols, such as urolithins, together with glycomacropeptide and POS, appear to be key mediators. However, clinical validation in major neurodegenerative diseases remains fragmented. Standardized formulations, mechanistic trials, harmonized endpoints, and precision-nutrition strategies are required to confirm their therapeutic potential.