Mediterranean diet works by adding up small improvements

Eating a Mediterranean-type diet won’t suddenly and dramatically improve your cholesterol, magically slash your blood pressure, or help you drop 20 pounds overnight.

But if you stick with it over time, it can potentially cut your risk of heart and blood vessel diseases by as much as 25%, according to a study published online Dec. 7, 2018, by JAMA Network Open. This overall improvement may be due to the cumulative effect of numerous small positive changes that occur in the body as a result of the diet — most notably, a drop in chronic inflammation, a known risk factor for heart disease.

“Eating a traditional Mediterranean diet can protect people from their first heart attack or first stroke to the same extent as statin medication, and it’s even more protective than low-dose aspirin therapy,” says Dr. Samia Mora, an associate professor of medicine at Harvard Medical School and one of the study’s authors.

What’s in the Mediterranean diet?

The Mediterranean-type diet is based on an eating pattern historically followed in countries around the Mediterranean, such as Spain, Greece, and Southern Italy — although many people in these regions have now strayed from this dietary pattern.

Mediterranean-style meals are built on a foundation of vegetables, fruits, and whole grains. Animal protein is used more sparingly than in a traditional Western-style diet and most often consists of lean meats and fish — and only small amounts of red meat. The diet also includes moderate amounts of cheese and yogurt.

The diet also includes lots of olive oil, as well as nuts, seeds, and legumes.

To switch to a Mediterranean-style diet, make small changes to your daily meals over time. Simple strategies include

  • adding more vegetables to each of your daily meals
  • swapping butter and other fats for extra-virgin olive oil
  • switching out refined carbohydrates, such as crackers and rice, for whole grains and whole-wheat breads
  • periodically trading servings of red meat for beans or lean meat options
  • reducing your intake of sugars and refined carbohydrates — for instance, by eating a serving of fresh fruit instead of your usual sweet treat.

The Mediterranean-type diet may be more challenging for people who live in a food desert, an area where it’s difficult to find fresh fruits or vegetables. But it can be done by using frozen vegetables and beans, says Dr. Samia Mora, an associate professor of medicine at Harvard Medical School. “In general, it’s healthier to prepare legumes yourself rather than relying on canned legumes, which can be loaded with salt,” she says. “If you do use canned beans, be certain to rinse them thoroughly to eliminate as much of the added sodium as possible.” Also, beware of added sodium in nuts. Opt instead for unsalted raw or dry roasted nuts and seeds.

A heart-healthy diet

It’s really no surprise that researchers found health benefits from the Mediterranean-style diet, which is heavy in lean meats and fish, olive oil, whole grains, legumes, and fruits and vegetables and low in processed foods and sugary deserts. Researchers have long known that the Mediterranean diet appears to protect against cardiovascular disease. But nobody knew exactly why the Mediterranean diet produced those benefits. What specifically does the diet change within the body that helps heart health?

Dr. Mora and her fellow researchers from Harvard Medical School, the Harvard T.H. Chan School of Public Health, and Brigham and Women’s Hospital embarked on their study to find out. They looked for clues in 25,000 participants in the Women’s Health Study, examining the women’s diets as well as 40 different biomarkers. They then compared that information against data on which of the women went on to have heart attacks, arterial blockages, or strokes over the course of the approximately 12-year follow-up period.

Not only did they find that women whose diets most closely resembled a traditional Mediterranean pattern were a quarter less likely to have heart and blood vessel problems than those whose diets least resembled that model, they also used the biomarker information to get a better picture of exactly what was different about people who were eating a Mediterranean-style diet versus those who weren’t.

Biomarker data showed that women eating a Mediterranean-style diet had improvements in some important measures. Compared with women who didn’t eat a Mediterranean-style diet, women who did saw drops in heart and blood vessel risks of

  • 29% from a reduction in inflammation, which is a known contributor to heart disease
  • 27.9% from improved glucose metabolism and a reduction in insulin resistance
  • 27.3% from lower body mass index.

Researchers also saw improvements in blood pressure, cholesterol levels, and other biomarkers, but these were less significant.

“We were not expecting that all these pathways would be affected by the diet,” says Dr. Mora.

The drop in chronic inflammation appeared to provide the largest degree of risk reduction. “We were surprised that the contribution of inflammation was even stronger than the effect on blood pressure and glucose metabolism,” says Dr. Mora.

Other factors may also be at play in Mediterranean diet

Future research may look at other factors that may also make the Mediterranean diet beneficial, says Dr. Samia Mora, an associate professor of medicine at Harvard Medical School.

Some believe that the Mediterranean diet may have a beneficial effect on your digestive tract and the 100 trillion bacteria and other microorganisms that live within it. Research is revealing the importance of a diverse and healthy intestinal microbiome (the microbial community in the gut), which is now thought to play a role in immune function and healing inflammation inside the body. It’s thought that the Mediterranean-style diet, which includes low-sugar Greek yogurt and other fermented foods, may contribute healthy organisms to the microbiome. Some of its positive health effects may stem from those contributions. “We did not have a measure for that in our study,” says Dr. Mora.

Future research on the diet may also look specifically at the role extra-virgin olive oil plays in the dietary benefits of the Mediterranean-style model. Extra-virgin olive oil is believed to prevent a type of irregular heartbeat known as an arrhythmia, and it’s also thought to reduce breast cancer risk. Other research has revealed potential associations with lower risks for diabetes and dementia, says Dr. Mora.

Reaping the benefits

The more closely women followed the Mediterranean diet, the more improvements they saw on average, says Dr. Mora. But that doesn’t mean you need to be perfect to see health benefits from dietary changes. Try to follow the Mediterranean diet 80% to 90% of the time, but you can allow yourself some room to stray — provided it stays within that 10%–20% range.

However, you will need to stick with the Mediterranean-style pattern over time to see a real reduction in cardiovascular risks. This is not a short-term fix, says Dr. Mora; instead, view it as a lifestyle change. “It needs to be done consistently,” she says.

But this study shows that embarking on this approach is likely to bring tangible benefits. Many people are more likely to change their lifestyle if they know how it is going to benefit them. “A lot of us are curious, why should I do this? Knowing how something works is helpful,” says Dr. Mora.

The good news is that unlike some popular fad-type diets, the Mediterranean model is relatively easy to follow. “The Mediterranean diet is actually very well tolerated, and many people can adhere to it over the long term,” says Dr. Mora. And, she adds, it offers a lot of choice in food selection and doesn’t require counting calories. “This is a nonrestrictive diet. Even without calorie counting, this eating plan could help with weight control. On average, there was a reduction in body mass index among those in the study who complied most closely with the Mediterranean-style diet, but the changes were small.

However, Dr. Mora said it’s important to note that while women on the diet didn’t see a lot of weight loss, the diet may have helped prevent weight gain in some instances, because many of the Mediterranean-style eaters in the study maintained their body weight as they entered menopause, when they otherwise might have gained.

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