February 24, 2020
Eating a Mediterranean diet (MedDiet) for just 1 year improved diversity in the gut microbiome of elderly participants and was associated with reduced frailty and better health, according to the results of a randomized multicenter study published online February 17 in the journal Gut.
"[A]dherence to the MedDiet modulates specific components of the gut microbiota that were associated with a reduction in risk of frailty, improved cognitive function, and reduced inflammatory status," write Paul W, O'Toole, PhD, from University College Cork, Ireland, and colleagues.
In the current study, researchers enrolled 612 test subjects between the ages of 65 and 79 years from five different European countries (Poland, Netherlands, United Kingdom, France, and Italy). Subjects were randomly assigned to either a control group (n = 289) who would consume their standard diet, and an intervention group (n = 323) who were instructed to adhere to a Mediterranean-style diet for 12 months. The Mediterranean-style diet focused on increased consumption of vegetables, fruits, whole grains, legumes, and fish and a decrease in dairy products, red meat, alcohol, and sugar.
Upon entry into the study, participants were categorized as being non-frail or pre-frail and underwent baseline medical exams and gut microbiome testing.
After 12 months, O'Toole and colleagues found that subjects who adhered to the MedDiet had greater microbiome diversity when compared to those in the control group.
Moreover, they found that the improved microbial diversity was associated with improvements in markers of frailty, including hand strength, walking speed, and cognitive function. A more diverse microbiome was also associated with a decrease in inflammatory markers including C-reactive protein and interleukin-17. These associations remained after adjusting for confounders such as age and body mass index.
Upon examination of the specific microbiota present, O'Toole and colleagues found that the enriched bacterial populations present in the intervention group produced more short-chain fatty acids (SCFAs), which have been associated with improved health. Conversely, the bacterial populations that decreased over the course of the intervention were those that produced bile acids, which have been associated with detrimental effects such as insulin resistance and nonalcoholic fatty liver disease.
The researchers suggest that the increase in microbiome diversity noted among those in the intervention group is likely the result of greater exposure to key nutrients including fiber, vitamins such as vitamin C and thiamine, and increased consumption of minerals such as copper, iron, and manganese.
Of note, despite the fact that microbiomes differed between participants from different countries at baseline, the gut microbiomes of those who adhered to the MedDiet were similar at the end of the intervention, suggesting that "keystone species" linked to positive outcomes remain stable regardless of location.
"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," write the investigators.
The authors acknowledge that these results are observational and note that a Mediterranean diet may not be feasible for many elderly people depending on the availability of ingredients or the presence of medical conditions that could hinder their ability to eat a specific diet.
"The interplay of diet, microbiome, and host health is a complex phenomenon influenced by several factors," the authors write. However, "our findings support the feasibility of improving the habitual diet to modulate the gut microbiota, which in turn has the potential to promote healthier aging."
Funding for this study was provided, in part, by Science Foundation Ireland. The authors have disclosed no relevant financial relationships.