Mediterranean diet can alter gut microbiome to promote health

Last Updated: 2020-02-26

By Marilynn Larkin

NEW YORK (Reuters Health) - Following a Mediterranean diet for a year can alter the gut microbiome in older people, potentially improving health and staving off frailty, randomized trial data show.

"We had tried previously to improve the microbiome and health of older people in a small cohort in Ireland by supplementing their diet with a mixture of five prebiotic fibers, but the effects were modest," Dr. Peter O'Toole of University College Cork in Ireland told Reuters Health by email. "So we needed to try something more drastic - to change the whole diet of (more than) 600 people for one whole year, in five countries."

"We already knew that a MedDiet was good for health," he said. "What we did not know was that consuming this diet changes our internal microbial ecosystem - the gut microbiome - and probably this (is what) makes the diet work. It is not just the food ingredients that are healthy, but how it is converted into beneficial metabolites by the bacterial community it stimulates in the gut."

Dr. O'Toole and colleagues profiled the gut microbiota of 612 adults ages 65 to 79 from the UK, France, Netherlands, Italy and Poland before and after they followed a Mediterranean diet intervention tailored for older people (NU-AGE diet) for a year. The diet was rich in fruits, vegetables, nuts, legumes, fish and olive oil and low in red meat and saturated fats.

As reported in Gut, 323 patients were assigned to follow the NU-AGE MedDiet and 289 were assigned to a control group. Overall, adherence to the Mediterranean diet led to increased abundance of specific taxa that were positively associated with several markers of less frailty and improved cognition, and negatively associated with inflammatory markers, such as C-reactive protein and interleukin-17. The associations were independent of factors such as age and body mass index.

Microbial metabolite profiling showed that microbiome changes were associated with an increase in short/branch chained fatty acid production that are beneficial to health; the changes were also associated with lower production of secondary bile acids, p-cresols, ethanol and carbon dioxide, overproduction of which is associated with the onset of colorectal cancer, insulin resistance, non-alcoholic fatty liver disease and cytotoxicity.

Positive associations were also seen for three measures linked to frailty - the Fried score; hand-grip strength and gait time - and for measures associated with cognitive function. "It's worth noting that what we saw was a slowing down of the rate of frailty onset over the one-year course of the trial, not frail people becoming non-frail," Dr. O'Toole said.

Additional analyses showed that the bacteria that proliferated in response to the diet act as "keystone species," meaning they are important for a stable gut ecosystem. Further, the microbiome changes were driven mainly by an increase in consumption of fiber, vitamins (C, B6, B9, thiamine) and minerals (Cu, K, Fe, Mn, Mg).

Dr. O'Toole said, "We are now studying the bacteria whose abundance was increased on the MedDiet to see if we identify in lab culture exactly what they do to promote health."

Dr. Bill Sullivan, Showalter Professor of Pharmacology and Toxicology, Microbiology and Immunology at Indiana University School of Medicine in Indianapolis, commented in an email to Reuters Health, "The premise of the study...is sound, particularly since the Mediterranean diet is consistently linked to better health outcomes and a longer lifespan. Previous studies have shown that the microbiome is adversely affected in the guts of elderly people, showing a decrease in the overall types of bacteria and a bias towards those that are pro-inflammatory."

That said, he added, "This is an encouraging start, but it would be helpful to see if these results hold up in more diverse populations. A person's genes are also believed to impact microbiome composition, so there is a complex interplay between genetics, environment, and microbes to consider."

"In addition," he noted, "these types of study show correlations, not causation. A healthier diet may be producing better health outcomes for reasons other than - or in addition to - changing the gut microbiome."

"We are only at the beginning of understanding how diet impacts the microbiome and what consequences that has on health and longevity," Dr. Sullivan said. "It is likely to be of importance in people of all ages."

SOURCE: https://bit.ly/2uuwQlQ Gut, online February 17, 2020.