New research has found that older people who adhered to a Mediterranean diet for a year had healthier gut microbiomes and improved measures of frailty.
Mediterranean-type diets — rich in vegetables, legumes, nuts, and whole grains and typically excluding red meat — have been the subject of numerous studies about health and nutrition.
A new study conducted by specialists from institutions in eight countries — including the University of Bologna, in Italy, and University College Cork, in Ireland — is now adding to the list of potential benefits brought on by a Mediterranean diet.
The researchers — who report their findings in the journal Gut — worked with data from a cohort of more than 600 older adults in five countries. They found that, across the spectrum, a Mediterranean diet seemed to improve aging individuals’ gut health and reduce frailty.
The first author of the study paper is Tarini Shankar Ghosh, Ph.D., from the APC Microbiome Ireland research institute.
The study’s authors point out that previous research has suggested that a simple dietary intervention such as switching to a Mediterranean-style diet might reduce frailty in older people.
This is important because frailty involves the gradual breakdown of multiple systems at once, often involving widespread, low-grade inflammation that further contributes to poor health.
To verify that switching to a Mediterranean diet could lower measures of frailty, the researchers involved in the current study recruited 612 individuals aged 65–79.
Medical exams showed that 28 of the study participants qualified as “frail,” 151 were on the verge of frailty, and 433 showed no signs of frailty.
The participants came from France, Italy, the Netherlands, Poland, or the United Kingdom.
Of the total number, 323 individuals (141 men and 182 women) agreed to follow a Mediterranean-type diet for 1 year, while the rest continued with their usual diets and acted as a control group.
The Mediterranean diet involved was rich in vegetables, legumes, fruits, nuts, olive oil, and fish. It featured very little red meat and few dairy products or saturated fats.
To understand the diet’s effects on the health of older individuals, the researchers started by examining the impact on gut health.
That was because previous studies have suggested that older individuals — particularly those who live in residential care facilities — tend to have less healthy gut microbiotas, possibly as a result of more restrictive diets.
In turn, an unhealthy gut corresponds to poorer overall health and faster onset of frailty in older adults.
When the researchers compared the compositions of the gut microbiomes of participants who had followed a Mediterranean diet for a year with those of participants who had followed their usual diets, they found significant differences.
Stool samples revealed that after 12 months on the Mediterranean diet, the participants had better bacterial diversity in the gut, compared with peers from the control group.
Moreover, better gut bacterial diversity was associated with improved markers of frailty, including better walking speed, better handgrip strength, and improved cognitive functioning.
Participants who had adhered to the Mediterranean diet also displayed fewer markers of chronic low-grade inflammation.
Looking more closely at what was happening in the participants’ guts, the researchers found that health improvements were associated with richer populations of bacteria that produce beneficial short-chain fatty acids, on the one hand, and decreased populations of bacteria that produce bile acids, on the other.
The researchers explain that when bacteria release too much of certain bile acids, it is associated with an increased risk of insulin resistance, fat buildup in the liver, cell damage, and even bowel cancer.
According to the researchers, the positive changes were likely thanks to the Mediterranean diet having provided a consistent source of key nutrients, including dietary fiber and crucial vitamins and minerals, such as vitamins C, B-6, and B-9, as well as copper, potassium, iron, manganese, and magnesium.
When they adjusted their findings for potential confounding factors, such as age and body mass index, the investigators observed that the associations between the Mediterranean diet and better gut health remained in place.
The team also noted subtle differences in participants’ microbiome changes, depending on the countries that they lived in, which speaks to the independent influences of other environmental factors.
Regardless of these variations, all of the people who followed the Mediterranean diet showed the same overall improvements in gut and systemic health, the researchers emphasize.
Although they caution that their research was observational, and thus cannot point to a direct causal relationship, the investigators write that:
“By protecting the ‘core’ of the gut microbial community, adherence to the [Mediterranean] 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 [individuals].”
While they continue to maintain that the Mediterranean diet is, overall, beneficial, the researchers acknowledge that it may be impractical for some older people — an obstacle that healthcare professionals will have to contend with.
“In some older [people] with problems like dentition, saliva production, dysphagia, or irritable bowel syndrome, adapting a [Mediterranean diet] may not be a realistic option,” the researchers caution in their study paper.