The so-called Mediterranean diet is already considered one of the healthiest for your heart, and now scientists say it may give your gut bacteria a boost, too.
The diet is typically high in fruits, vegetables, nuts, beans, olive oil and fish, and low in red meat and saturated fats. The new study finds that older adults who eat a Mediterranean diet tend to have more types of gut bacteria linked with healthy aging.
One nutritionist wasn't surprised, and believes that the diet's reliance on vegetables could be key to the effect.
"Dark green leafy vegetables, nuts and seeds all have multifold benefits in enhancing our gut microbiome," said Sharon Zarabi, a registered dietitian who directs the bariatric program at Lenox Hill Hospital in New York City. She wasn't involved in the new research, which was led by Dr. Paul O'Toole, a microbiologist at University College Cork, in Ireland.
According to O'Toole's team, prior research has suggested that a poor diet can have a negative impact on an older person's strength and stamina, as well as their microbiome -- the trillions of bacteria living in the human digestive tract.
In their study, the researchers tracked how a Mediterranean diet affected the microbiomes of more than 600 people, aged 65 to 79, who were living in France, Italy, the Netherlands, Poland and the United Kingdom.
The participants were either already frail (28), on the verge of frailty (151), or not frail (433).
Their gut microbiomes were assessed before and after 12 months of either eating their usual diet or a Mediterranean diet that had been specially tailored to older people.
Eating the Mediterranean diet for a year was tied with a number of beneficial changes to the gut microbiome.
For example, the diet seemed to help stem the loss of diversity in bacterial species in the gut -- a more diverse microbiome is thought to be healthier. The Mediterranean diet was also tied to a rise in bacterial species that have long been associated with keeping people physically and mentally stronger as they age. In addition, the diet was linked to a lower production in the gut of potentially harmful inflammatory chemicals, the team said.
Moreover, the Mediterranean regimen was associated with a rise in gut bacteria that produce beneficial "short chain fatty acids," and a decline in bacteria that help make certain bile acids. Overproduction of those bile acids has been connected to an increased risk of colon cancer, insulin resistance (a precursor to diabetes), unhealthy "fatty" liver and cellular damage, O'Toole's team said.
The beneficial gut microbiome changes associated with eating a Mediterranean diet were largely due to increases in dietary fiber and associated vitamins and minerals, such as vitamins C, B6, B9, and copper, potassium, iron, manganese and magnesium.
Despite the findings, the study wasn't designed to make a direct link between the gut microbiome and health in older adults, the researchers stressed.
Still, diet can exert a powerful influence on people's health, Zarabi believes.
Any enhancement of diet and the microbiome "has a strong connection to the brain and cognitive development," she noted. The Mediterranean diet is "chock full of vitamins and minerals," is thought to boost gastrointestinal function, and even "induces weight loss by keeping us full," she added.
The study was published Feb. 17 in the journal Gut.
The American Heart Association has more on the Mediterranean diet.