Mediterranean Microbiome
We initially found that those who followed the Mediterranean diet had better cognitive function and memory, less inflammation, and better bone strength. However, what we really wanted to know was whether or not the microbiome was involved in these changes.
Interestingly, but not surprisingly, a person’s baseline microbiome (the species and number of microbes they had living in their gut before the study started) varied by country. This baseline microbiome is likely a reflection of the diet they usually ate, alongside where they lived. We found that participants who followed the Mediterranean diet had a small but insignificant change in their microbiome diversity—meaning there was only a slight increase in the overall number and variety of species present.
However, when we compared how strictly a person followed the diet with their baseline microbiome data and their microbiome after following the diet, we were able to identify two different gut microbe groups: diet-positive microbes that increased on the Mediterranean diet, and diet-negative microbes whose abundance was reduced while following the diet.
Diet-positive microbes are microbes that flourished in the Mediterranean diet. Diet-negative microbes either couldn’t metabolize the diet, or they were unable to compete with diet-positive microbes. These diet-positive microbes were linked with 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.
When we compared the changes in the number of these microbes in the treatment group (those on the Mediterranean diet) and the control group (those following their regular diet), we saw that the people who strictly followed the Mediterranean diet increased these diet-positive microbes. Although the changes were small, these findings were consistent across all five countries—and small changes in one year can make for big effects in the longer term.
The link between frailty, inflammation, and cognitive function to changes in the microbiome was stronger than the link between these measures and dietary changes. This suggests that the diet alone wasn’t enough to improve these three markers. Rather, the microbiome had to change too—and the diet caused these changes to the microbiome.
These types of studies are challenging and expensive, and the microbiome dataset is often difficult to analyze because there are many more data-points to study than there are people in the study. Our findings here were possible because of the large group sizes, and the length of the intervention.
However, we recognize that following a Mediterranean diet isn’t necessarily doable for everybody who starts thinking about aging, usually around the age of 50. Future studies will need to focus on what key ingredients in a Mediterranean diet were responsible for these positive microbiome changes. But in the meantime, it’s clear that the more you can stick to a Mediterranean diet, the higher your levels of good bacteria linked to healthy aging will be.