The gene that causes type 2 diabetes can also cause stroke, but a Mediterranean diet neutralizes this risk.

A new study published in Diabetes Care shows the gene that predicts type 2 diabetes risk also increases a person’s likelihood of having a stroke. But there’s good news: if a person eats a Mediterranean diet, this increased risk disappears.

The gene, called TCF7L2 turns dozens of other genes and pathways on or off. “TCF7L2 is expressed in a broad [..] pattern, including tissues with important roles in glucose metabolism, such as brain, liver, skeletal muscle, fat, and bones,” explained Dr. Jose M. Ordovas, Director of the Nutrition and Genomics Laboratory at the USDA Jean Mayer Human Nutrition Research Center on Aging at Tufts University, in an interview with Healthline.

The gene has been associated with diabetes risk for many years, but its effects on stroke were unknown until now.

In a study that followed 7,018 people, dubbed PREDIMED (PREvención con DIetaMEDiterránea), Ordovas found a link between diet and stroke risk.

Participants were randomly assigned to one of three groups: a Mediterranean diet high in extra virgin olive oil; a Mediterranean diet high in nuts; and a control group on a low-fat diet. The researchers followed them for five years. The result was that those participants with the TCF7L2 gene who were on either Mediterranean diet had no increased rate of stroke at all.

With the exception of genes on the Y-chromosome (and the X, in men), everyone has two copies of each gene, one from their mother and one from their father. For TCF7L2, the high-risk version of the gene is called the T, and the low-risk version is called the C. Someone with two copies of C, who would be called CC, is at low genetic risk for type 2 diabetes and stroke. A person with two copies of T, called TT, is at higher risk. A CT person, with one copy of each gene, gains partial protection against diabetes and stroke, although environmental factors still play a role.

“The most recent estimates indicate that the heritability for stroke is about 40 percent,” says Ordovas. “However, keep in mind that there are different types of strokes and they can vary.” His study only examined stroke risk caused by this specific gene.

The T version of the gene is found most widely among African Americans, Native Americans, and European Americans, particularly those of Mediterranean rather than Northern European descent. It’s less common among Asian Americans, particularly those of Chinese ancestry.

In Ordovas’ study, TT subjects on a Mediterranean diet had no greater stroke risk than CC subjects who ate the control, low-fat diet.

The Mediterranean diet includes lots of fresh fruits and vegetables, nuts, beans and legumes, yogurt and cheese, and complex carbohydrates. Animal protein comes from eggs and moderate amounts of fish and poultry, with very little red meat. Olive oil is the primary source of fat, and is used widely in cooking.

Unlike many diets, the Mediterranean diet isn’t particularly low in fat. Rather, it’s the type of fat that makes all the difference.

American diets are high in saturated and trans fats, which are found in red meat, processed foods, and fried foods. The Mediterranean diet features monounsatured and polyunsaturated fats. There are not only less calorie-dense than their saturated counterparts, but they also make the body metabolize saturated fats more efficiently, lowering cholesterol and heart disease risk. Olive oil and nuts are both rich in monounsaturated fats.

“The PREDIMED study design provides us with stronger results than we have ever had before,” said Ordovas in a press release. “With the ability to analyze the relationship between diet, genetics, and life-threatening cardiac events, we can begin to think seriously about developing genetic tests to identify people who may reduce their risk for chronic disease, or even prevent it, by making meaningful changes to the way they eat.”