Mediterranean diet promotes healthy aging with healthier gut microbiome

By Dr. Liji Thomas, MDFeb 17 2020

A new study published online in the journal Gut in February 2020 reports the striking health-promoting effects of switching to a Mediterranean diet for just one year. The results were due to an increase in the health and number of gut bacteria that favor a healthy diet.

Aging is an inevitable process, but the associated loss of bodily functions and increased inflammatory conditions cause increased frailty in older people. The importance of this diet is that it appears to modulate the gut bacteria in a way that is beneficial to prevent the loss of physical vigor and cognitive impairment with advancing age.

Earlier studies show that a poor diet with a restricted variety of foods is both a common pattern with older people and one which accelerates the onset of physical frailty because it narrows the range of bacteria found in the gut. This is especially so when it comes to older people who are living in long-term nursing homes and other residential facilities.

Mediterranean diet intervention alters the gut microbiome in older people reducing frailty and improving health status: Marian Weyo / Shutterstock

The study

A Mediterranean diet is one that is rich in fruits, vegetables, nuts, legumes, olive oil, and fish but has small amounts of red meat, saturated fats.

The current study focused on the benefits that a Mediterranean diet might produce in terms of healthier gut microbiome, whether it might shift the gut bacterial population and subtypes in a direction that is favorable to retaining and increasing the number of bacteria that are associated with healthy aging.

In the study, which spanned five countries (France, Italy, Netherlands, Poland, and the UK), the researchers examined the gut microbiome of about 600 people aged 65 to 79 years, with one sample at baseline and a second sample after 12 months on a typical Western diet or a Mediterranean diet that was adapted to fit the needs of older people. The first group contained about 290 people, and the second about 320 people.

All the participants were classified as physically frail or on the edge of frailty (about 180 people), or not frail (about 430 people) at baseline.

The findings

At the beginning of the study, the participants fell into three subgroups based on their dietary profiles as well as their gut microbiomes – the Italians, the French and English, and the Dutch and Polish subjects.

The Mediterranean diet was found to be linked to beneficial changes in the gut microbiome when followed for 12 months. The loss of bacterial diversity was reduced, while the types of bacteria that are found to mark clinical features that accompany less frailty went up. These indicators include walking speed and strength of handgrip, as well as better brain function, including memory. They are also associated with lower levels of inflammatory chemicals that could harm the individual’s health. These include C-reactive protein and Interleukin-17.

A closer look shows that these changes are also linked to a higher number of good bacteria, those that produce short-chain fatty acids that contribute to health. Concurrently, there is a lower number of bacteria that are known to produce specific bile acids, p-cresols, ethanol, and carbon dioxide. These chemicals can harm the person if produced in excess, by increasing the risk of colon cancer, and metabolic damage like insulin resistance, fatty liver, and cell damage.

The bacteria whose numbers increased were also found to be what is called ‘keystone’ species. In other words, their presence in adequate quantities is essential to maintaining the stability of the gut microbiome. On the other hand, the other species that are known to be linked to the markers of increased frailty are not vital to the gut ecosystem.

The findings remained constant even after controlling for age, body mass index, and the presence of multiple disease conditions, also though these factors modulate the composition of the gut microbiome.

Secondly, even though the participants came from different countries with obviously different dietary practices, the findings showed that despite the fundamental difference in gut microbiome composition, the final response at 12 months of following this diet remained strikingly similar across national borders.

Again, the time frame of the change in the diet and the microbiome seems to show that the latter is more important in its association with health improvement markers.

The researchers say the microbiome changes are most closely linked to the increase in dietary fiber, which includes additional vitamins and minerals. The micronutrients they found to be increased included vitamins C, B1, B6, B9, iron, copper, potassium, manganese, and magnesium. On the other hand, the controls showed a higher level of saturated fat intake compared to the Mediterranean diet group.

Inferences

The investigators inferred that the changes in the microbiome were probably more important in improving the health of the participants on the Mediterranean diet than the diet itself, which may have served as the agent.

They say the study adds support to an exciting principle that “microbiomes of healthy individuals are similar and the unhealthy individuals are each aberrant in their way.”

They computed a “microbiome index’ and examined its associations with the earlier measures of frailty, cognitive function, and inflammation. They found that 10 of the 11 associations in the positive direction (improved health) and many negative associations were replicated or newly discovered. They feel that this shows that the microbiome components are not just indirect reflections of the diet, but independently associated factors linked to indicators of improved health.

Implications

Though this study doesn’t prove that the gut microbiome changes cause the reduction in frailty, it does emphasize the role played by the diet in the microbiome composition, which in turn affects the health of the human host.

They postulate, “By protecting the ‘core’ of the gut microbial community, adherence to the diet could facilitate the retention of a stable community state in the microbiome, providing resilience and protecting from changes to alternative states that are found in unhealthy subjects.”

Even though some of the conclusions they reached are inferences rather than directly measured outcomes, they say, “The interplay of diet, microbiome and host health is a complex phenomenon influenced by several factors. 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.”

For instance, some older and weaker people may not be able to chew or swallow firm foods like vegetables and some fruits. In such a scenario, the study could help develop useful treatments in the form of live bacterial formulation for ingestion by identifying the bacteria that are associated with healthy aging. This could perhaps serve to delay the onset and progress of frailty.