As the population ages, the incidence of age-related neurodegenerative diseases is rapidly increasing, and novel approaches to mitigate this soaring prevalence are sorely needed. Recent studies have highlighted the importance of gut microbial homeostasis and its impact on brain functions, commonly referred to as the gut–brain axis, in maintaining overall health and wellbeing. Nonetheless, the mechanisms by which this system acts remains poorly defined. In this review, we will explore how (poly)phenols, a class of natural compounds found in many plant-based foods and beverages, can modulate the gut–brain axis, and thereby promote neural health. While evidence indicates a beneficial role of (poly)phenol consumption as part of a balanced diet, human studies are scarce and mechanistic insight is still lacking. In this regard, we make the case that dietary (poly)phenols should be further explored to establish their therapeutic efficacy on brain health through modulation of the gut–brain axis, with much greater emphasis on carefully designed human interventions.

Alzheimer's disease (AD) is projected to increase in prevalence, heightening the need for strategies to alleviate its neuropathological burden. The bioactive constituents of a Mediterranean-style diet are well-recognised for their neuroprotective properties. Due to their capacity to alter the gut microbiome composition, these benefits may involve modulation of the microbiota-gut-brain axis. In this study, we investigated whether a novel supplement enriched with key Mediterranean diet-derived bioactives (Neurosyn240) could reduce amyloid deposition and microglial activation in 5xFAD mice, a transgenic model of AD, through microbiota-mediated mechanisms. Male and female 5xFAD transgenic mice (n = 16 per sex) were randomly assigned to receive either a standard control diet or a diet supplemented with Neurosyn240 for 12 weeks. Employing a multi-omics approach, gut microbiota composition was profiled using 16S rRNA ampliconsequencing, serum metabolites were quantified via targeted metabolomics, and hippocampal gene expression was analysed through qPCR and RNA sequencing. Neuropathological markers, including amyloid-β deposition and microglial activation, were evaluated using immunofluorescence staining. Statistical analyses were performed using two-way ANOVA to examine the main effects of diet and sex and their interaction. Neurosyn240 significantly shifted the gut microbiome composition, which was associated with increased circulatory serotonin levels and decreased kynurenine and bile acids (TCA, HDCA, TDCA, CDCA and LCA) concentrations. In the brain, Neurosyn240 consumption led to a significant reduction in hippocampal amyloid deposits and Iba-1 positive microglia (p<0.05), which were associated with decreased LCA and increased serotonin, respectively. Hippocampal RNA sequencing further highlighted the upregulation of genes involved in promoting amyloid beta clearance mechanisms. Together, these findings highlight novel neuroprotective effects of Neurosyn240 in modulating metabolite-mediated pathways of the microbiota-gut-brain axis, accentuating its therapeutic potential against AD progression.

At the end of October 2024, ILSI Europe brought together industry and academic experts from different fields to identify research gaps and challenges in nutritional interventions supporting healthy ageing. The objectives of the Healthy Ageing Working Group workshop were to address the urgent need to define ageing outcomes and associated biomarkers, determine the trajectory of functional ageing across the lifespan, and leverage technology to tailor nutritional and lifestyle interventions for healthy ageing. This brief report presents the key points highlighted during this workshop.