Mediterranean Diet Alters Gut Microbiome, Lengthens Life

Many popular diets, such as keto, paleo, or Whole30, can help people lose weight temporarily, but many healthcare professionals are divided on whether these diets are beneficial for overall health. Generally speaking, that isn’t the case with the Mediterranean diet, which calls for eating whole foods including vegetables, fruits, whole grains, and fish, as well as drinking a little red wine. It’s one of the few diets that finds general favor. In fact, the Dietary Guidelines for Americans, published by the U.S. Department of Health and Human Services and the U.S. Department of Agriculture, recommend following a Mediterranean-style eating pattern to help improve health and prevent chronic disease.

A study published in February 2020 in the journal Gut suggests another benefit of the Mediterranean diet: improving the gut microbiome of older adults and reducing frailty. “The beneficial effect of a Mediterranean diet appears to be due, at least in part, to its effect on the gut microbiome — the community of organisms that lives in our intestines and that converts many raw food ingredients into beneficial compounds that the body can use,” says a coauthor of the study, Paul O’Toole, PhD. Dr. O’Toole is a professor and researcher of microbial genomics in the school of microbiology at University College Cork in Ireland.

Aging naturally leads to increased frailty and can include what the authors call “inflammaging,” which is the development of chronic low-grade inflammation, loss of cognitive function, and chronic diseases such as type 2 diabetes and atherosclerosis.

Reducing frailty translates into elderly people being more capable of independent living because they can walk steadily, not lose their balance and fall, and generally take care of themselves for as long as possible, says O’Toole.

Theories About the Microbiome and Human Health

The microbiome refers to the 100 trillion microbes that live in and around us, says William R. DePaolo, PhD, an associate professor of medicine at the UW Medical Center and the director of the center for microbiome sciences and therapeutics in Seattle. Dr. DePaolo was not involved in the new research. “Most of the microbes are confined to our gastrointestinal tract, and they increase in number as you go from stomach to anus,” he says.

The microbiome is responsible for a number of critical functions in human health, the most obvious being our ability to digest food, says DePaolo. “It also contributes to our immune health,” he says.

The gut microbiota generate metabolites that are important for gut health and general systemic health, says DePaolo. “It’s structural, it’s immunological, it’s metabolism — in a way, it has its tendrils in everything,” he says.

How Lifestyle Habits Change the Gut Microbiome

Your microbiome evolves from the time you are born until your early teens, says DePaolo. “Once you hit puberty, your microbiome is pretty stable until you are an older adult — that’s the last sort of change that occurs. Aging is one of the things that we definitely know changes the microbiome,” he says.

A study published in Nature suggested that the microbiome of older people, especially those who live at long-term care facilities, is less healthy than the microbiomes of younger people.

Your microbiome can shift if you drastically change your lifestyle, says DePaolo. “For example, if you’re a vegan and all of a sudden you start eating meat, that’s going to shift your microbiome as an adult. If you have chronic stress or chronic anxiety, that’s going to shift it as well,” he says.

How these shifts may contribute to disease is still unclear, though. “We see changes in the microbiome when a person has a disease or inflammation, but we don’t know if that’s a cause or a consequence,” says DePaolo. “Does the disease cause the microbiome to change or do changes in the microbiome lead to the development of the disease? We don’t know that yet,” he says.

Reducing Inflammation and Improving the Microbiome Through Dietary Changes

For the study, 612 people ages 65 to 79 were given medical exams and put into one of three groups. Twenty-eight people were considered “frail,” 151 on the verge of frailty, and 433 did not show any indications of frailty.

To determine the effects of the Mediterranean diet, researchers measured inflammation and fat-related hormones and extracted microbial DNA from stool samples from all participants at the start of the study.

Three hundred and twenty-three people followed a Mediterranean diet for a year, while the remaining 289 participants served as the control group and continued eating their normal diet. The Mediterranean diet group increased consumption of vegetables, legumes, fruits, nuts, olive oil, and fish, and ate less red meat, dairy products, and saturated fats.

After a year, investigators took stool samples from all participants for a second time to compare changes. The people on the Mediterranean diet had a healthier and more diverse microbiome, and fewer markers of inflammaging than the people who had remained on their normal diet. These effects were true even after researchers controlled for participants’ age, body mass index (BMI), sex, medical conditions, or medications. The microbiome of the control group stayed the same.

The study authors say that improvements in the gut bacteria were associated with improvements in the markers used to measure frailty, which includes a faster walking speed, improved handgrip strength, and better cognitive functioning.

O’Toole explains that these improvements likely come from the “bloom of bacteria” that can breakdown the ingredients of the Mediterranean diet, like cereals and legumes. “These bacteria generate short-chain fatty acids and other chemicals that provide energy and health. At the same time, these bacteria out-compete undesirable bacteria that can cause inflammation,” he says.

This study was large and well designed, and shows that there were significant changes in the microbiome over the course of a year through dietary modification, says DePaolo. “I don’t think there has been other work that has definitely shown that,” he adds.

“It would be interesting to see what would have happened if researchers had included another diet in this study — like one that emphasized fats or was high in sugar — to see if the same changes in the microbiome occurred,” says DePaolo. There is a chance that these improvements in the gut could have happened as the result of the stress or shock that can come with any major diet shift and not necessarily as a result of the Mediterranean diet, he says.

Manipulating the Microbiome: Risks Are Still Coming to Light in This New Field

It’s important to remember that microbiome research is less than 10 years old, says DePaolo. “Things in the field are changing every day,” he says.

“All the food you eat, the air you breathe, and the stress you feel — it’s so unique to you, and that largely determines your microbiome. Because it is so personal, it’s hard to make broad statements about the shifts that will be brought about by things like diet changes or fecal transplants,” says DePaolo. He, as well as the U.S. Food and Drug Administration, point out that some people have died from fecal transplants.

Because everyone’s microbiome is different and research is in its infancy, be skeptical of outlandish claims. That includes any products or companies that promise specific health benefits from examining your microbiome via a stool sample.

Following a Healthy Lifestyle Is the Path to a Healthy Gut Microbiome

Changing your gut microbiome by way of improving your diet may be a worthy effort. The current study findings indicate that people should eat as many Mediterranean diet foods as possible, says O’Toole.

Future research may explore the effects of the microbiome in younger people, and try to develop pure cultures of bacteria to restore the missing microbes in the guts of frail older people who consume a restricted diet, he adds.

For most people, good gut health can be achieved by practicing commonsense health habits, says DePaolo. “Get a good night’s sleep, eat your fiber, take a probiotic if you want, eat fermented foods, try to eat fruits and vegetables and exercise a little bit, and your microbiome will be good. Gut health doesn’t have to be complicated.”