Aging is a condition associated with systemic physiological decay, characterized by chronic inflammation, cognitive impairment, and frailty. Well-established findings support the Mediterranean Diet (MedDiet) as a valid strategy to address frailty, also due to its modulatory effect on gut microbiota. The NU-AGE dietary intervention project is a large cohort of more than 1200 elderly individuals from different European countries treated with a customised MedDiet for one year. A recently published study explored the effects of this particular diet on the gut microbiota of a subsample of 612 participants.
Authors reported the association between microbiome and adherence to the MedDiet by the identification of ‘positive’ or ‘negative diet-responsive taxa’, respectively with previous reported positive or negative health associations, largely shared across the entire cohort. The association between diet-responsive taxa and specific indices of frailty, cognitive function and inflammation across the entire study cohort, showed that diet-positive taxa had negative association with inflammatory markers and positive association with better cognitive function, despite of country specific variations in dietary intake, microbiota and adherence scores to Mediterranean diet.
Testing the associations between diet-responsive taxa and the consumption patterns of specific dietary components characterising the NU-AGE MedDiet, emerges that taxa with an increasing positive association with diet adherence scores are highly positively correlated with the consumption of total fibre, vitamin C and D, plant proteins and carbohydrates, and highly negatively correlated with alcohol, fats and sugar. According on the overall correlations and the abundances marker taxa in a given sample, a sample-specific diet-modulated microbiome index was calculated, showing positive correlation with improvement in cognitive function and physical well-being and negative association with inflammation.
These effects seem to be driven by specific microbial metabolites, that the authors identified by predicting the functional metabolic profiles of the gut microbiota using corresponding 16S species composition profiles. Positive changes in gut microbiota were associated with an increase in the microbial consumption of fibre-associated non-starch polysaccharides and short chain fatty acids (SCFAs) production, whereas negative changes were associated with an increase in microbial simple sugar consumption and bile acids derivates. These results indicate that positive or negative metabolic changes are associated with a positive or negative microbiota response, with a direct impact on host’s health.
The evaluation of the role of diet-responsive taxa on the overall microbiome structure, through network representation, showed that diet-positive taxa are central in the gut community structure, whereas diet-negative taxa were more peripheric. Despite issues represented by high individual microbiome variability, authors identified diet-responsive taxa and diet-associated microbiome index through a comprehensive machine-learning methodology, in order to predict adherence to the MedDiet. These improvements permitted to identify specific components of the gut microbiota which can reduce frailty, cognitive impairment and inflammation.
It is important to comment that the study only test associations between adherence to MedDiet and gut microbiota profile and its metabolites with frailty, therefore causality is not tested. Furthermore, if the MedDiet reduces the risk of frailty, we might expect that the participants who have high adherence to the MedDiet will be less frail than those who did not. However, no association was observed between adherence to the MedDiet and the frailty of participants over the duration of the study. Considering several issues related to the validity of a dietary strategy to promote health, the challenging matter highlighted by the authors, after the identification of health-associated taxa, is to develop in the future novel biotherapeutic compounds for direct administration to subjects more exposed to frailty.