Mediterranean diet may protect against diabetes more than realized, study finds

Blood biomarkers showed a nearly 30% reduction in type 2 diabetes risk in people who ate a diet rich in whole grains, fish, vegetables and olive oil.

The Mediterranean diet has already been shown to help protect the aging brain and may significantly lower risk of heart disease. A new study has now found a much stronger link than previously realized between the Mediterranean diet — which is filled with whole grains, fish, fruits and olive oil — and a reduced risk of Type 2 diabetes.

Previous research looking at the impact of a Mediterranean diet on diabetes have shown mixed results, possibly because the studies were based on participants remembering and self-reporting the type of food they ate.

For the new research, published Thursday in PLOS Medicine, British scientists used blood samples to develop a biomarker scoring system. They first ran a small trial, called the Medley trial, with 128 adults ages 65 and older who were randomized to consume either the Mediterranean diet or continue eating as they usually did for a period of six months.

A comparison of blood samples from the two groups turned up a host of biomarkers of fatty acids and carotenoids, the substances that give color to vegetables such as pumpkins, carrots and tomatoes.

For the second part of the research, scientists from the University of Cambridge, in the U.K., analyzed data — including blood samples and self-reported diet information — from more than 340,000 middle-aged participants in a long-running European study. Over about 10 years, 9,453 had developed Type 2 diabetes.

Then the researchers compared biomarker scores from the 9,453 to 12,749 randomly selected participants without diabetes in the large study.

They found a nearly 30% reduction in diabetes risk using the biomarker data, compared to 10% reduction from the self-reported data. That means previous studies probably underestimated the impact of the Mediterranean diet.

The findings strengthen the case for recommending the Mediterranean diet for the prevention of Type 2 diabetes, said senior author Dr. Nita Forouhi, a professor of population health and nutrition and program leader in nutritional epidemiology at the University of Cambridge.

“The 20% of participants with the highest values of the biomarker score had a 62% lower risk of new-onset type 2 diabetes relative to the 20% with the lowest biomarker score values,” Forouhi said in an email.

What is a Mediterranean diet?

For someone consuming an average of 2,000 calories per day, researchers defined it as, at least:

• 2 to 3 tablespoons of olive oil.
• Five servings of vegetables (75 g each).
• Two to three servings of fruits (150 g each).
• Five servings of cereal products (between 30-120 g each depending on the specific product).

And a daily maximum of:

• One medium potato.
• One serving of milk (250 mL).
• Two glasses of red wine (150 mL each).

Weekly recommendations included:

• Six servings of Greek low-fat yogurt (170 g each).
• One to three servings of poultry (100 g each).
• At least five servings of nuts (35 g each).
• At least three servings of legumes (75 g each).
• At least three servings of fish (150 g each).

And a maximum of:

• Four servings of cheese (40 g each).
• One serving of red meat (100 g).
• Five eggs.

Dr. Peter Goulden, chief of the division of endocrinology, diabetes and bone diseases at Mount Sinai Morningside and Mount Sinai West, called the new biomarker scoring an exciting development.

“If you compare the biomarker score with self-reports, the effect is three times larger,” said Goulden, who is also an associate professor at the Icahn School of Medicine at Mount Sinai. “So that’s very powerful.”

Further studies will be needed to corroborate the findings and determine if they would apply to a wider population, he said.

A downside is the biomarkers don’t determine whether the benefits are from fruit and vegetable consumption or some other aspect of the diet, said Linda Van Horn, a clinical nutrition epidemiologist at the Feinberg School of Medicine, Northwestern University in Chicago.

Still, this approach “is more objective, so I would say it’s a step in the right direction,” she said.

The importance of the findings is underscored by the rising rates of diabetes around the world, said Dr. Anna Beth Bradley, an assistant professor of medicine, diabetes, endocrinology and metabolism at the Vanderbilt University School of Medicine.

“If you look at the prevalence of diabetes globally, you see that in Europe, the incidence is around 6% to 7%, while in the U.S., it’s around 11%, which suggests that the standard American diet probably has contributed to the rise in diabetes,” Bradley said. “That terrible American diet is leaking over to other countries with diabetes rising in pretty much every country.”