Beneficial effects of the Mediterranean Diet in overweight and obese subjects

Beneficial effects of the Mediterranean Diet on the composition and function of the gut microbiome, systemic metabolome and cholesterol levels in an overweight population at risk of developing cardiovascular disease. They are shown by a European study, coordinated by the University of Naples Federico II, in collaboration with the University of Copenhagen and the French MetaGenoPolis Institute.

The research, just published in the prestigious scientific journal Gut, highlights how there is a direct relationship between diet, the gut microbiome and human health.

Partners in the European project DINAMIC - Diet-induced Arrangement of the gut Microbiome for Improvement of Cardiometabolic health - conducted an 8-week randomized controlled nutritional intervention study in overweight and obese subjects with sedentary lifestyles. The results clearly show that a change in dietary behavior, without any concomitant change in individual energy intake of macronutrient intake and physical activity, can reduce blood cholesterol levels, as early as after 4 weeks, in a population at high cardio-metabolic risk for poor lifestyle. In addition, increased adherence to the Mediterranean diet induces changes in the gut microbiome and its function, which are important for human health. Consistent with aspects of personalized nutrition, the data show that some individuals harbor a gut microbiome that is more susceptible to Mediterranean diet-induced changes and go on to experience additional clinical benefits such as improved insulin sensitivity and inflammatory status.

The multidisciplinary team featured the research groups of faculty members Danilo Ercolini, Paola Vitaglione and Angela Rivellese of the Federico II Task Force for Microbiome Studies; Lars O. Dragsted and Henrik M. Roager from the Department of Nutrition, Exercise and Sport at the University of Copenhagen; and members of the research team from the French research institute MetaGenoPolis (INRAE) at the University of Paris-Saclay coordinated by Dusko S. Ehrlich.

Analyzed, then, the effect of the Mediterranean diet on the composition of the gut microbiome and on clinical, metabolic and anthropometric parameters of 82 healthy, overweight and obese subjects at risk of developing cardiovascular disease. Participants were included in the Mediterranean diet intervention group (n=43) or the control group (n=39). Participants in the Mediterranean diet group received an individual diet plan on the Mediterranean model, equivalent to the usual one in calories and macronutrient composition. Then these volunteers increased their intake of dietary fiber, plant protein, and unsaturated fat and reduced simple carbohydrates, animal protein, and saturated fat. Volunteers in the control group did not change their eating habits for the duration of the study. All volunteers maintained the sedentary lifestyle during the intervention period.

By analyzing data from metagenomics, analysis of the genomes of all components of the gut microbiome, and metabolomics, analysis of metabolites, the microbiome and metabolome profile of the study population was defined contextually with clinical and anthropometric data.

After 4 weeks, volunteers consuming a Mediterranean diet showed a reduction in total plasma cholesterol compared with controls. In addition, volunteers who increased adherence to the MD the most also showed an increase in fiber-degrading and short-chain fatty acid-producing bacteria, such as certain strains of Faecalibacterium prausnitzii, an enrichment in the triglyceride-degrading pathways of butyrate metabolism, and a decrease in potentially pro-inflammatory species, e.g., Ruminococcus gnavus. Adherence to the Mediterranean diet was demonstrated with an increase in consumption markers of foods of plant origin and a decrease in those of foods of animal origin such as lower plasma and urinary levels of carnitine and animal protein degradation products. With regard to microbial metabolites of health-related and diet-related interest, an increase in urine levels of urolithins, molecules with anti-inflammatory properties produced by the gut microbiota from polyphenols present in nuts, was shown. Finally, a reduction in fecal bile acid production and insulin resistance was observed, and these changes were correlated with basal levels and changes in the microbial species involved in these specific metabolic features.