Can adopting a Mediterranean diet have further health benefits for older people?
Frailty is one of the by-products of the aging process. As people get older, they naturally tend to become frailer and, as a result, are at an increased risk of inflammation and/or fractures. However, although frailty cannot be avoided completely, it can be slowed or delayed. The idea of a Mediterranean diet has frequently been associated with healthier aging. What exactly is a Mediterranean diet? A Mediterranean diet is one that is high in vegetables, fruits, fish, and oils like olive oil, but low in red meat, dairy, and saturated fats. Adherence to this kind of diet has been shown to reduce the risk of certain diseases and it has also been suggested that it could reduce frailty in older adults.
It is this link with frailty that provides the impetus behind a new study published in the journal Gut (1). The authors explored a potential link between the Mediterranean diet and changes in the gut microbiome, which may be associated with reduced frailty. The project was a 12-month, randomised, controlled dietary intervention. Older, frail, or pre-frail individuals in five European countries (Italy, UK, Netherlands, Poland, and France) had their microbiome analysed at the beginning of the project. They were then assigned to either the control group (usual diet) or the intervention group (a specific Mediterranean-style diet called the MedDiet). After 12 months, microbiome profiles were repeated.
In total, 612 individuals completed all aspects of the study. Interestingly, adhering to the MedDiet was associated with a reduction in microbiome diversity. However, this effect was lessened by increasing adherence to the diet. When individual bacterial species were examined, some were found to be increased by greater adherence to the MedDiet, whilst others were reduced. The majority of these affected bacterial species have previously been associated with various diseases such as type-2 diabetes or colorectal cancer, indicating a potential mechanism by which the MedDiet may impact disease risk.
Overall, the effects of the MedDiet on specific species were positive from a health perspective. Bacterial species with negative health associations were hindered by the diet whilst those associated with protective or health-boosting effects prospered. Specifically examining the issue at the heart of this study, frailty, several of the bacterial species enriched by the MedDiet have been associated with reduced frailty risk and improved cognitive function. The results suggest that the MedDiet has the potential to reduce frailty risk in older adults.
However, there are limitations to this study. For example, the extra degree of separation between the intervention (MedDiet) and the main outcome of interest (frailty) limits the impact of the findings. The MedDiet may impact the risk of frailty, but it does not appear to do so directly. Instead, it alters the gut microbiome, and it is these alterations that are associated with a reduced risk of frailty. As a result, the study highlights correlation, rather than causality. It does not provide sufficient evidence to say that the MedDiet reduces the risk of frailty. Furthermore, if the MedDiet was reducing the risk of frailty, we might expect the participants who adhered to the diet to be less frail than those who did not. However, there was no observed association between adherence and the frailty of participants over the timeframe of the study.
Although the results of this study are not particularly impactful, it does highlight that the MedDiet appears to have an overall positive impact on the microbiome and may alter levels of specific bacteria that are associated with reduced frailty. Further research is needed both to establish the strength of the impact of the MedDiet on the microbiome and also on how strong this association between microbiome makeup and frailty is.
Written by Michael McCarthy
1.Ghosh TS, Rampelli S, Jeffery IB, Santoro A, Neto M, Capri M, et al. Mediterranean diet intervention alters the gut microbiome in older people reducing frailty and improving health status: the NU-AGE 1-year dietary intervention across five European countries. Gut. 2020:gutjnl-2019-319654.
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