It has been known for some time that the “Green Mediterranean diet” – rich in nuts, vegetables, olive oil and legumes and without any red or processed meat – is recommended for the prevention of heart disease and metabolic diseases (such as Type 2 diabetes). It has now been found by researchers at Ben-Gurion University (BGU) of the Negev in Beersheba that the health-promoting effects previously attributed to the Green Mediterranean diet, are in fact influenced by the changes in the gut microbiome and have a striking effect on the bacteria of the human gut.

The standard Mediterranean diet aims to follow the traditional eating patterns of Mediterranean cultures, with the consumption of whole grains, fruits, vegetables, beans, herbs, spices, nuts, and olive oil and a minimum of red meat. These are supplemented with fish or seafood about twice a week, along with moderate amounts of dairy, eggs, and poultry. 

This diet discourages eating red meat and sweets, and encourages people to steer clear of processed foods that are often packed with added sugars and sodium. This eating plan also allows you to drink up to one glass of red wine per day (though if you don’t already drink, you’re not encouraged to start).

The Green Mediterranean diet, however, avoids red and processed meat entirely, while placing plants in the spotlight in a way that goes above and beyond that of the standard Mediterranean diet. It includes traditionally “good” Mediterranean-style foods, like whole grains and fresh produce, but in addition, it includes daily consumption of 100 grams of a shake that includes Mankai duckweed (a protein-rich aquatic plant that is high in bioavailable protein, iron, B12, vitamins, minerals, and polyphenols), three to four cups of green tea and one ounce (28 grams or a quarter cup) of walnuts. 

In a large-scale clinical interventional trial – called the DIRECT PLUS – the gut microbiome of Green Mediterranean dieters was enriched with bacteria that are known to have a significant effect on human weight and glycemic (sugar) control. 

The study was published today in Genome Medicine under the title “The effects of the Green Mediterranean diet on cardiometabolic health are linked to gut microbiome modifications: a randomized controlled trial.” 

The research was led by Prof. Iris Shai, director of the Health and Nutrition Innovative International Research Center at BGU’s Faculty of Health Sciences and an adjunct Professor in the Harvard School of Public Health, together with her MD-PhD student Dr. Ehud Rinott, Prof. Ilan Youngster from Shamir Medical Center in Tzrifin, Tel Aviv University and several selected international experts. 

The DIRECT PLUS trial research team, led by Shai, was the first to introduce the concept of the Green-Mediterranean diet. The team found that the green, plant-based diet better optimizes the microbiome for  the autologous fecal microbiota transplantation (aFMT) procedure, in which are transplanted orally into the same individual. When this is performed, the Green Mediterranean diet can promote the remission of fatty liver, improve LDL (“bad”) cholesterol, glycemic control, CRP (C-reaction protein, a marker of inflammation) and blood pressure control and minimize age-related brain atrophy, as compared to the traditional Mediterranean diet. 

The results showed that while all diets induce substantial changes to the gut microbiome community, the changes of Green Mediterranean dieters are much more pronounced. 

Interestingly, the beneficial changes in the gut of Green Mediterranean dieters were attributed to the tendency of this novel diet to specifically affect the rare bacteria in the subjects’ intestines. This phenomenon was possibly due to the fact that the prominent component of the diet, duckweed, is new to the Western palate, allowing usually concealed microbes to flourish under the new gut environment induced by the plant. 

The Green Mediterranean diet induced specific microbial changes, including enrichments in the genus Prevotella, bacteria known for their positive effects on glucose metabolism and insulin sensitivity, while also promoting genetic pathways involved in the reduction of branched-chain amino acids, compounds that are well linked to insulin resistance. 

Lastly, the researchers were able to show that by modifying specific gut microbes through dieting, the gut microbiome constitutes a valuable mediator between the green dietary pattern, and its effects on weight loss and reduced cardiac risk. 

“These findings can strengthen our understanding regarding the significant cross-talk between our nutritional intake, the microbiome and clinical outcomes,” said Shai. “We aim to discover how the Green Mediterranean diet affects the health of its consumers.”

The favorable clinical results were substantial,” added Rinott, first author and colleague at the BGU School of Public Health. “We hope that by unraveling the role of the gut microbiome in the diet’s effect, we can further improve and personalize diets in the future.”

“These results are another example illuminating the central role of our gut microbiome in health and disease and will further our understanding in this intriguing field,” concluded Youngster.