Green Mediterranean diet: what links between cardiometabolic health and gut microbiota?

It is a diet that is now unanimously recommended by the international learned societies of cardiology and diabetology. ^2,3,4 Epidemiological studies show that the Mediterranean diet is associated with better general health and a significant reduction in cardiometabolic risks.  Recent studies go further and suggest an additional benefit on morbi-mortality of the reduction of animal proteins and fats in favor of their vegetable equivalents (nuts, seeds, olive oil, etc.) in the Mediterranean diet.

Green-Med, a diet based on plants and their polyphenols

Researchers have conducted a study corroborating these results while providing a better understanding of the role of the microbiota in these effects. They randomized 294 participants from the DIRECT-PLUS⁵ cohort over 30 years of age (88% men) with abdominal obesity and/or dyslipidemia into three groups: standard healthy diet recommendations, Mediterranean diet and "Green-Med", an "optimized" Mediterranean diet. The Green-Med incorporates Mankai duckweed (100 g per day), an Asian plant rich in fiber and plant protein that reduces the amount of meat, and green tea (3 to 4 cups per day). The authors highlighted the high content of polyphenols in these foods, which are capable of modifying the taxonomic structure of the intestinal microbiota and intervening in fat metabolism. ⁶ Both diets were supplemented with nuts (28g per day) and were isocaloric and restrictive (1500-1800 kcal for men and 1200-1400 kcal for women). All three groups combined the diet with moderate physical activity.

Changes in the structure and enzymatic activity of the microbiota

Fecal samples from the participants were collected and analyzed by sequencing at baseline and at 6 months. All subjects showed changes in the structure of their gut microbiota. Green-Med led to even more substantial changes, mainly in its rare (<50%), person-specific, and diet-influenced species. Specifically, it led to an increase in Prevotella, signaling adherence to a "vegetarian" diet, and a decrease in Bifidobacteria, known to improve dietary glycemic index and facilitate weight loss. The researchers also found a reduction in the biosynthesis of branched-chain amino acids, metabolites involved in obesity and insulin resistance. 

Superior results on weight and cardiometabolic markers

The Green-Med was more effective in terms of weight loss (-6.5% vs -5.4% for the Mediterranean diet and -1.58% for the standard diet). In addition, improvements following a similar trend were observed on markers of cardiovascular risk, with a decrease in Framingham score, waist circumference, mean blood pressure, insulin resistance and plasma leptin levels.

 According to the researchers' modelling, these benefits are partly related to the impact of changes in the microbiota caused by Green-Med, contributing for example to 12% of the weight loss and 18% in the reduction of the Framingham score.