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The Mediterranean diet increases gut bacteria

Die mediterrane Ernährung erhöht die Darmbakterien

The Mediterranean diet increases gut bacteria associated with healthy aging in older adults

As our global population looks set to live longer than ever before, we must find ways to help people live healthier lives for longer. Exercise and diet are often cited as the best ways to stay healthy well into our lives. But more recently, research has also begun to look at the role our gut — specifically our microbiome — plays in our aging.

Our latest study found that a Mediterranean diet causes microbiome changes associated with improvements in cognitive function and memory, immunity, and bone strength.

The gut microbiome is a complex community of trillions of microbes that live semi-permanently in the gut. These microbes evolved with humans and other animals to break down food components like inulin, arabinoxylan, and resistant starch that humans cannot digest. They also help prevent the growth of disease-causing bacteria.

However, the gut microbiome is extremely delicate, and many things, including diet, the medications you take, your genetics, and even conditions like inflammatory bowel disease and irritable bowel syndrome can alter the gut microbiota community. The gut microbiota plays such a huge role in our bodies that it's even been linked to changes in behavior, including anxiety and depression. But like other microbiome-related diseases like type 2 diabetes and obesity, changes in the microbiome are only part of the problem – the person's genetics and poor lifestyle are major contributors.

Because our daily diet has such a major impact on the gut microbiome, our team was curious to see if it could be used to promote healthy aging. We studied a total of 612 people aged 65 to 79 from the UK, France, the Netherlands, Italy,d Poland. We asked half of them to switch their regular diet to a Mediterranean diet for a full year. This included eating more vegetables, legumes, fruits, nuts, olive oil, and fish, and eating less red meat, dairy, and saturated fats. The other half of the participants stayed on their usual diet.

Mediterranean microbiome

We first found that those who adhered to the Mediterranean diet had better cognitive function and memory, less inflammation, and better bone strength. However, what we wanted to know was whether or not the microbiome was involved in these changes.

Interestingly, but not surprisingly, a person's baseline microbiome (the type and number of microbes they had in their gut before the study began) varied from country to country. This baseline microbiome likely reflects the diet they typically ate, along with where they lived. We found that the participants who adhered to the Mediterranean diet exhibited a small but insignificant change in their microbiome diversity—meaning that the overall number and diversity of species present increased only slightly.


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However, when we compared how strictly an individual followed the diet with their baseline microbiome data and their post-diet microbiome data, we were able to identify two distinct groups of gut microbes: diet-positive microbes, which increased on the Mediterranean diet, and diet-negative microbes, whose frequency increased during of the diet was reduced.

Diet-positive microbes are microbes that thrived in the Mediterranean diet. Diet-negative microbes either could not metabolize food or be unable to compete with diet-positive microbes. These diet-positive microbes have been linked to less frailty and inflammation in the body and higher levels of cognitive function. Losing the diet-negative microbes was also associated with the same health improvements.

Those who stuck to the Mediterranean diet had healthier microbes in their gut.
Those who stuck to the Mediterranean diet had healthier microbes in their gut.

When we compared the changes in the number of these microbes in the treatment group (those following a Mediterranean diet) and the control group (those following their normal diet), we found that the people who strictly followed the Mediterranean diet had these positive diet increased microbes. Although the changes were small, these results were consistent across all five countries — and small changes in one year can have big long-term effects.

Many of the participants were also prefrail (meaning their bone strength and density are beginning to decrease) at the start of the study. We found that the group that followed their normal diet became more frail over the course of the year-long study. However, those who adhered to the Mediterranean diet were less frail.

The association between frailty, inflammation, and cognitive function with changes in the microbiome was stronger than the association between these interventions and dietary changes. This suggests that diet alone was not enough to improve these three markers. Rather, the microbiome also had to change – and diet caused these changes in the microbiome.

These types of studies are sophisticated and expensive, and the microbiome dataset is often difficult to analyze because there are many more data points to examine than there are people in the study. Our results here were possible because of the large group size and the length of the intervention.

However, we recognize that a Mediterranean diet isn't necessarily feasible for everyone who starts thinking about aging, usually around 50. But in the meantime, it's clear that the more you can stick to a Mediterranean diet, the higher it gets Your levels of good bacteria may be associated with healthy aging.


Paul O’Toole

Professor für Mikrobielle Genomik, School of Microbiology und APC Microbiome Institute, University College Cork

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