Mediterranean Diet May Prevent Diabetes

Tomatoes, onions, garlic and other vegetables, along with olive oil sit on a white table.
(Image credit: Vegetables and olive oil photo via Shutterstock)

Following a Mediterranean diet may help prevent diabetes in people who are at risk for heart disease, even if they do not also lose weight or increase exercise, a new study from Spain suggests.

In the study, people at risk for heart disease who followed a Mediterranean diet — which consisted mostly of fruits, vegetables, whole grains, fish and fats from either extra-virgin olive oil or nuts — were about 30 percent less likely to develop type 2 diabetes over a four-year period than people who were advised to follow a low-fat diet.

Participants who supplemented their diet specifically with fats from extra-virgin olive oil were 40 percent less likely to develop diabetes during the study compared with those who followed a low-fat diet. [5 Diets That Fight Diseases]

None of the participants were advised to cut calories or increase physical activity, and most had little change in their body weight during the study period.

Previous studies had found that weight loss and exercise can prevent diabetes, but the new findings suggest that changes in diet alone may reduce the risk of developing this chronic disease, at least in some people.

The study involved mostly white, older adults (ages 55 to 80) who were at high risk for heart disease, so the findings may not apply to other populations, the researchers said.

Mediterranean diet benfits

In the study, 3,541 older adults living in Spain were assigned to follow one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts or a low-fat diet. None of the participants had diabetes at the start of the study, but they had at least three risk factors for heart disease (such as high blood pressure, high cholesterol, history of smoking, obesity or a family history of heart disease).

Each year, participants answered questions about what they ate, to confirm they were sticking to their assigned diet. Some participants had their blood and urine analyzed for markers that would indicate they were consuming extra-virgin olive oil or nuts.

During the study, 273 participants developed diabetes: 80 people (6.9 percent)eating the Mediterranean diet with extra-virgin olive oil, 92 people (7.4 percent) eating the Mediterranean diet with nuts; and 101 people (8.8 percent) eating a low-fat diet.

After taking into account factors that could affect diabetes risk — such as total calorie intake, physical-activity level and alcohol intake — participants who followed the Mediterranean diet with extra-virgin olive oil had a reduced risk of developing diabetes compared with the group following a low-fat diet. Those who followed a Mediterranean diet supplemented with nuts also had a reduced risk of diabetes, but this particular finding could have been due to chance.

Diet vs. exercise

The study was originally designed to look at the effect of a Mediterranean diet on heart-disease outcomes, and last year, researchers found the diet was associated with a reduced risk of heart attacks and strokes. After this study was completed, researchers restudied the collected data to see whether a Mediterranean diet also prevented diabetes. Because the study was not originally designed to look at diabetes prevention, the current finding that a Mediterranean diet can prevent diabetes is suggestive rather than definitive, said Dr. Pieter Cohen, an assistant professor of medicine at Harvard Medical School and a general internist at Cambridge Health Alliance.

But Cohen, who was not involved in the current study, does not think another large study is necessarily needed to confirm the results relating to diabetes prevention. "We already know these two diets are good for your heart," Cohen said, referring to the Mediterranean diet with extra-virgin olive oil or nuts. "Why not go with the diet now?" Cohen said.

The new findings do not take away from exercise and weight loss as methods to help prevent diabetes, Cohen said. Rather, the findings suggest that the Mediterranean diet has its own additional benefits, Cohen said.

Dr. Robert Graham, an internist at Lenox Hill Hospital in New York, said that following a Mediterranean diet is really a lifestyle change — which includes cooking your own food and paying attention to what you put in your body. It is this lifestyle, and not a single "magic bullet," that helps people get healthy, said Graham, who was not involved in the research.

The study, published today (Jan. 6) in the journal Annals of Internal Medicine, was funded by the Spanish government's Instituto de Salud Carlos III. Olive oil and nuts were donated by industry groups.

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Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.