While the data continues to pour in on the benefits of the Mediterranean diet for cardiac health, the lack of information on how this diet affects the aging process has not gone unnoticed by the scientific community. As such, an international team of investigators, led by researchers at the University of Cork, set out to determine the effects of the Mediterranean diet on older populations. Amazingly, the five-country study found that eating a Mediterranean diet for a year boosts the types of gut bacteria linked to “healthy” aging while reducing those associated with harmful inflammation in older people.

The researchers published their findings yesterday in Gut through an article titled “Mediterranean diet intervention alters the gut microbiome in older people reducing frailty and improving health status: the NU-AGE 1-year dietary intervention across five European countries.”

“Aging is accompanied by deterioration of multiple bodily functions and inflammation, which collectively contribute to frailty. We and others have shown that frailty co-varies with alterations in the gut microbiota in a manner accelerated by consumption of a restricted diversity diet,” the authors wrote. “The Mediterranean diet (MedDiet) is associated with health. In the NUAGE project, we investigated if a one-year MedDiet intervention could alter the gut microbiota and reduce frailty.”

Previous research suggests that a poor/restrictive diet, which is common among older people, particularly those in long term residential care, reduces the range and types of bacteria (microbiome) found in the gut and helps to speed up the onset of frailty.

The researchers, therefore, wanted to see if a Mediterranean diet might maintain the microbiome in older people’s guts and promote the retention or even proliferation of bacteria associated with “healthy” aging.

“We profiled the gut microbiota in 612 non-frail or pre-frail subjects across five European countries (U.K., France, Netherlands, Italy, and Poland) before and after the administration of a 12-month long MedDiet intervention tailored to elderly subjects (NU-­AGE diet).”

They analyzed the gut microbiome of individuals aged 65 to 79, before and after 12 months of either eating their usual diet (n=289) or a Mediterranean diet (n=323), rich in fruits, vegetables, nuts, legumes, olive oil, and fish and low in red meat and saturated fats and specially tailored to older people (NU-AGE diet).

The participants, who were either frail (n=28), on the verge of frailty (n=151), or not frail (n=433) at the beginning of the study, lived in five different countries: France, Italy, Netherlands, Poland, and the U.K.

Interestingly, sticking to the Mediterranean diet for 12 months was associated with beneficial changes to the gut microbiome. Moreover, it was associated with stemming the loss of bacterial diversity; an increase in the types of bacteria previously associated with several indicators of reduced frailty, such as walking speed and handgrip strength, and improved brain function, such as memory, and with reduced production of potentially harmful inflammatory chemicals.

A more detailed analysis revealed that the microbiome changes were associated with an increase in bacteria known to produce beneficial short-chain fatty acids and a decrease in bacteria involved in producing particular bile acids, overproduction of which are linked to a heightened risk of bowel cancer, insulin resistance, fatty liver, and cell damage.

What’s more, the bacteria that proliferated in response to the Mediterranean diet acted as “keystone” species, meaning they were critical for a stable “gut ecosystem,” pushing out those microbes associated with indicators of frailty. The changes were largely driven by an increase in dietary fiber and associated vitamins and minerals—specifically, C, B6, B9, copper, potassium, iron, manganese, and magnesium.

Remarkably, the findings were independent of the person’s age or weight (body mass index), both of which influence the make-up of the microbiome. And while there were some differences in the make-up of a person’s gut microbiome, depending on the country of origin to start with, the response to the Mediterranean diet after 12 months was similar and consistent, irrespective of nationality.

The study findings can’t establish a causative role for the microbiome in health, added to which some of the implications are inferred rather than directly measured, according to the researchers.

“The interplay of diet, microbiome, and host health is a complex phenomenon influenced by several factors,” the authors emphasized. “While the results of this study shed light on some of the rules of this three-way interplay, several factors such as age, body mass index, disease status, and initial dietary patterns may play a key role in determining the extent of success of these interactions,” they explained.

Older people may have dental problems and/or difficulty swallowing, so it may be impractical for them to eat a Mediterranean diet, they added. But the beneficial bacteria implicated in healthy aging found in this study might yet prove useful therapeutic agents to ward off frailty.

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