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How a Mediterranean Diet Improves Health: Microbiome Diversity!

Have you ever wondered how the Mediterranean diet improves health? Several studies point to a beneficial impact on the gut microbiome.

There is a boatload of data suggesting that a Mediterranean diet improves health. A systematic review of dozens of studies concluded that such a diet can improve outcomes in cardiovascular disease, enhance the health of overweight patients and help prevent type 2 diabetes (Nutrients, March, 2019). But how does this kind of eating pattern lead to so many positive outcomes?

The Mediterranean Diet Improves Health by Altering the Microbiome:

Researchers have been trying to figure out how a Mediterranean diet improves health for many years. Some thought it must be the vegetables. Others insisted it was the olive oil. Many researchers believed that the whole grains provided the magic.

A large group of investigators from Europe believes that a Mediterranean diet improves health by changing the microbial balance of the digestive tract (Gut, online, Feb. 17, 2020). By now you have probably heard us talk about the microbiome (or the microbiota) dozens of times on our nationally syndicated public radio show. Here is a link to just one such radio show:

Show 1023: How to Rebalance Your Digestive Tract Bacteria
Are your digestive tract bacteria in good shape? If not, they could be contributing to heartburn and other forms of digestive distress.Show 1023: How to Rebalance Your Digestive Tract Bacteria

Listen to the streaming audio by clicking on the white arrow inside the green circle under the photo of our guest. You can also download the free mp3 file at the bottom of the page.

What Is the Microbiome?

Your body is teeming with microbes. Inside your digestive tract, for example, there are viruses, bacteria and fungi living together, but not always harmoniously. They help digest food, create vitamins and impact the immune system.

The Mediterranean Diet Study:

The European scientists set out to discover whether older people following a Mediterranean-type diet could increase microbial diversity, reduce inflammation and lower the likelihood of frailty. They recruited 612 older volunteers for this controlled trial.

Roughly half these people (who lived in Poland, Italy, the Netherlands, France and the UK) were switched to a Mediterranean diet for a year. The other half continued to follow their normal eating patterns. All participants had their gut microbes analyzed at the start and end of the study. The scientists also measured inflammatory markers.

The Outcome: The Mediterranean Diet Improves Health

The researchers found that people following a Mediterranean diet had changes in the ecology of their intestinal microbes. The new ecosystem was associated with lower frailty and better cognitive function.

The investigators conclude:

“our findings support the feasibility of improving the habitual diet to modulate the gut microbiota which in turn has the potential to promote healthier ageing.”

Why is this research important?

The authors note the:

“Significance of this study:

“►  Ageing is associated with deterioration of multiple bodily functions and inflammation, leading to the onset of frailty.
“►The onset of frailty is associated with changes in the gut microbiota that are linked with a restricted diversity diet.
“►  The Mediterranean dietary regime is positively associated with health.”

“What are the new findings?

“►  Adherence to the Mediterranean diet led to increased abundance of specific taxa that were positively associated with several markers of lower frailty and improved cognitive function, and negatively associated with inflammatory markers including C-reactive protein and interleukin-17.”

New Data Show a Mediterranean Diet for Weight Loss Improves Gut Microbes:

One of the first controlled trials of a traditional diet rich in vegetables and olive oil was the PREDIMED study. It demonstrated the heart health benefits of a Mediterranean diet. Now Spanish researchers have studied the benefits for weight loss and gut microbiota (American Journal of Clinical Nutrition, May 2024). They recruited 400 volunteers who had participated in the original PREDIMED trial.

The participants, between 55 and 75 years old, were evenly divided between a group that followed an unrestricted Mediterranean-style diet and a group that followed a low-calorie Mediterranean diet and exercised. The researchers collected blood and stool for analysis at the start of the study and after a year of intervention. Those in the intervention group got training from dietitians to reduce their energy intake and increase their physical activity. They had group and individual sessions as well as telephone support.

In the course of the year, the volunteers in the intervention group did lose weight. Their blood tests also showed improvement in blood sugar and lipids like cholesterol.

In addition, there were shifts in the distribution of gut microbes identified in the stool. Overall, the diversity of microbes increased, but there were decreases in certain microbes, specifically Eubacterium hallii. According to the investigators, this species ferments lactate and is especially common among people with insulin resistance. Presumably, decreasing levels are associated with better insulin sensitivity and blood glucose control. The scientists point out that both diets are healthful, but the intense intervention resulted in better gut health as well as weight loss.

What the Heck Is a Mediterranean Diet?

The Mediterranean is a big place! Just think about the countries that border the Mediterranean: Spain, France, Italy, Greece, Monaco, Malta, Cyprus, Turkey, Tunisia, Syria, Lebanon, Israel, Egypt, Libya, Algeria, Morocco, Bosnia, Croatia, Montenegro and Slovenia.

The people who live around the Mediterranean have different cuisines, but there are some fundamentals that they share. This dietary pattern is rich in vegetables and fruits and emphasizes legumes like lentils, beans and chickpeas. People eat whole grains, seeds and nuts. They are important components of the diet. Olive oil is highly prized and is a principal fat in many countries like Greece, Italy and Spain.

People who live in this region have traditionally consumed little sugar and not much meat, though they consume some fish and may drink moderate amounts of wine with their meals.

You can learn more about how to follow a Mediterranean diet from our book, The People’s Pharmacy Quick & Handy Home Remedies. In it, we provide details on the Mediterranean diet and what to eat to follow this eating pattern. You may also wish to read some related posts here and here.)

Can Probiotics Improve Gut Health?

When it comes to probiotics, the American marketplace is pretty much a wild west show. The Food and Drug Administration does not regularly monitor such products to verify that they contain what they claim. Consuming fermented foods such as kimchi, kombucha and sauerkraut as well as naturally fermented pickles is one way you can take in more of those beneficial bacteria. Those who tolerate dairy might also consider live-culture yogurt and kefir.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
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  • García-Gavilán JF et al, "Effect of 1-year lifestyle intervention with energy-reduced Mediterranean diet and physical activity promotion on the gut metabolome and microbiota: a randomized clinical trial." American Journal of Clinical Nutrition, May 2024. DOI: 10.1016/j.ajcnut.2024.02.021
  • Ghosh, T. S., 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, online, Feb. 17, 2020, doi:10.1136/ gutjnl-2019-319654
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