Mediterranean diets heavy in two foods -- olive oil and nuts -- are linked to a lower rate of strokes in older people whose genetic makeup boosts their risk of diabetes, according to a new study.
The research suggests but doesn't conclusively prove that the diet lowers or even eliminates the extra risk of stroke, perhaps by lowering the rate of diabetes. Still, "our work has placed a solid step on the ladder of personalized nutrition and successful health," said study co-author Jose Ordovas, director of the nutrition and genomics laboratory at Tufts University's USDA Human Nutrition Research Center on Aging.
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The so-called Mediterranean diet is thought to help citizens of Greece, Spain and southern Italy lower their rates of heart disease and cancer. While the diet has received tremendous attention in recent years, there's no firm definition of what it is because foods vary from region to region.
The Mediterranean diet is generally defined, however, as emphasizing olive oil, nuts, fresh produce and fish along with whole grains, seeds and healthier kinds of fat. There's less focus on dairy products and meat, and -- despite the Italian connection -- not much consumption of pasta.
In the new study, researchers randomly assigned more than 7,000 people aged 55 to 80 in Spain to eat a low-fat diet, or a Mediterranean diet high in nuts, or a Mediterranean diet high in extra-virgin olive oil. The researchers then followed the participants for an average of five years through 2010.
Some of the participants had a genetic trait in common: a mutation in a gene that boosts the risk of type 2 diabetes by as much as 50 percent compared to others with another form of the gene. Ordovas said that about 30 percent of whites have the riskiest form of the mutation.
Those with the mutation who went on the low-fat diet were nearly three times more likely than others to have a stroke, the investigators found. But those who went on the Mediterranean diets had about an equal level of risk as those without the genetic mutation.
The percentage of people in the various groups who suffered strokes ranged from 1.4 percent to 4.3 percent, Ordovas said.
"Switching to a Mediterranean diet is not going to hurt anybody, and it will help those people with risk factors or a family history of disease," Ordovas said. "However, if switching is not totally possible, then incorporating elements of this diet such as extra-virgin olive oil, nuts, veggies, fruits, will get you somewhere. Or better yet, exchanging less healthy items with those in the diet."
Robert Eckel, M.D., a professor of medicine and director of the Clinical and Translational Research Centers Network at the University of Colorado, who was not part of the study, said that the findings are useful. However, researchers still don't know how the genetic variations are related to diabetes and stroke risk, he said.
In general, Dr. Eckel said, the variations -- differences in DNA sequences between genes -- "are common and may have no effect, adverse effect or favorable impact on cardiac health, the risk of complications from diabetes, or both."
The finding were published online in the journal Diabetes Care.