Effects of Mediterranean Diet on plasma metabolites and their relationship with insulin resistance and gut microbiota composition in a crossover randomized clinical trial

The Mediterranean Diet (MedDiet) may decrease the cardiometabolic risk through modulation of metabolic pathways. Furthermore, the interplay between MedDiet, metabolites and microbial metabolism may improve our understanding on the metabolic effects of this diet. We aimed to evaluate the effect of the MedDiet compared to nuts supplementation on circulating metabolites and their relationship with cardiometabolic health. We further examined whether changes in the metabolomic profiles were associated with changes in gut microbiota composition in a multi-omics integrative approach.Forty-four adults with Metabolic Syndrome (MetS), (aged 37-65) participated in a randomized controlled, crossover 2-months dietary-intervention trial with a 1-month wash-out period, consuming a MedDiet or a non MedDiet plus nuts (50 g/day). Nutritional data were collected at the beginning and the end of each intervention period using 3-day dietary records, as well as fasting blood and fecal samples. Plasma metabolites (m = 378) were profiled using targeted metabolomics. Associations of these metabolites with the interventions were assessed with elastic net regression analyses. Gut microbiota composition was assessed by 16S rRNA sequencing. A sparse least regression analysis combined with a canonical correlation analysis was conducted between the plasma selected metabolites and genera in order to identify the relevant dual-omics signatures discriminating the dietary interventions.Changes in 65 circulating metabolites were significantly associated with the MedDiet (mainly lipids, acylcarnitines, amino acids, steroids and TCA intermediates). Importantly, these changes were associated with decreases in glucose, insulin and HOMA-IR. The network analysis identified two main clusters of genera with an opposite behaviour towards selected metabolites, mainly PC species, ChoE(20:5), TGs and medium/long-chain acylcarnitines.Following a MedDiet, rather than consuming nuts in the context of a non-MedDiet was associated with a specific plasma metabolomic profile, which was also related to metabolic improvements in adults with MetS. The identified correlated network between specific bacteria and metabolites suggests interplay between diet, circulating metabolites and gut microbiota. The trial was registered in the ISRCTN with identifier ISRCTN88780852, https://doi.org/10.1186/ISRCTN88780852.