The list of mental and physical attributes that decline with aging is long and well-known. Collectively our diminishing bodily functions contribute to increased frailty and more general inflammation. In the medical context, frailty includes not just weaker muscles and bones, but also reduced organ functions, decreased immunity, and cognitive decline. The combined negative changes can result in greater susceptibility to injury, disease, adverse drug reactions, and dementia, all things that we would prefer to avoid. Over the last 10 years, numerous studies examined the relationship of the gut microbiome to aging and health. Bacteria in our gut are critical not only for digesting food but also for producing metabolites that contribute to normal health. Healthy young adults have a rich diversity of bacterial species in their gut, and many of these species are known to make beneficial contributions to health. As we age our gut microbiome composition changes and often shows reduced diversity of bacterial species along with declines in beneficial species and increases in species that may be detrimental to good health. How and why these changes occur and exactly how these changes impact overall health are challenging questions that haven’t been resolved, though some studies suggest that these microbial changes contribute to frailty.
One important aspect of gut microbiology is the relationship between diet and microbiome composition. The Mediterranean diet (high in vegetables, legumes, fruit, nuts, olive oil, and fish but low in red meat, dairy, added sugars, and saturated fats) is known to promote a healthy microbiome. A new study in the journal Gut explored whether or not adopting a Mediterranean diet could improve the microbiome in the elderly and reduce frailty. A group of 612 individuals from 5 European countries ranging in age from 65-79 years old was divided into control (289 people) and test (323 people) cohorts. The control cohort maintained their normal diet while the test group changed to a Mediterranean diet. After 1 year, the test group showed better cognitive function, improvement in markers of frailty, and decreased inflammation. The improvements were seen regardless of their country of origin, age, or body mass index (BMI) which supports a direct Mediterranean diet effect and not some other confounding factor. Examination of the gut microbiome showed that the Mediterranean diet increased gut microbial diversity and seemed to stabilize key core microbial groups (see Figure 1 in the linked paper). The core groups are important for good health and typically produce beneficial metabolites. In contrast, people in the control group had less microbial diversity, reduced levels of the core groups, and higher levels of outlier organisms that produced detrimental metabolites. While some of the changes in the test group were modest, those who adhered most rigorously to the diet exhibited the most improvement in the tested markers. Improvement in microbiome function correlated with positive physical findings, suggesting a microbial contribution to these physiological changes.
This study is significant because it shows that aging-associated microbiome changes can be improved with dietary intervention. It’s too soon to predict if these observed positive changes (improved cognition, decrease frailty, and reduced inflammation) will be maintained over longer times if the diet is continued. Likewise, whether or not the positive changes actually improve quality of life or result in increased longevity has not been established. Nonetheless, these results do reinforce the concept that the Mediterranean diet supports a healthy microbiome which should improve general health and may reduce aging effects. It also suggests that you are never too old to change your diet, so next time you reach for a candy bar try some nuts instead.