A healthy diet and regular physical activity have long been recognized as cornerstones of type 2 diabetes prevention. Specifically, most healthcare providers steer people away from ultra-processed foods, refined carbs, and saturated fats in favor of more balanced choices. However, new research suggests that one well-studied approach to eating may offer an even stronger layer of risk protection.
In an August 2025 study published in the Annals of Internal Medicine, researchers from the Harvard T.H. Chan School of Public Health found that eating a Mediterranean-style diet—when done alongside regular exercise, reduced caloric intake, and professional weight loss support—cut the risk of developing type 2 diabetes by 31%. As defined by the Mayo Clinic, the Mediterranean diet focuses on “eating based on the traditional cuisines of countries bordering the Mediterranean Sea.”
The team from Harvard collaborated with researchers from 23 universities in Spain for the PREDIMED-Plus trial—the largest nutrition and lifestyle randomized clinical study in Europe. The trial followed 4,746 adults aged 55 to 75 who were overweight or obese and had metabolic syndrome but no prior diagnosis of diabetes. Participants were divided into two groups: the “intervention” group followed a traditional Mediterranean diet and reduced their caloric intake by 600 calories a day, moderate exercise such as brisk walking or strength training, and professional support for weight control; the “control group” followed the Mediterranean diet alone.
After six years, the results were striking. Those in the intervention group had a 31% lower risk of developing type 2 diabetes versus those in the control group. In addition to diabetes prevention, participants in the intervention group lost more weight (about 3.3 kilograms or 7.2 pounds) and reduced their waist circumference by 3.6 centimeter, compared to modest changes in the diet-only group.
“With the highest-level evidence, our study shows that modest, sustained changes in diet and lifestyle could prevent millions of cases of this disease worldwide,” said study co-author Frank Hu. MPH, MD, PhD, chair of Harvard’s department of nutrition, in a university news release.
Added co-author Miguel Martínez-González, MPH, MD, PhD: “In practical terms, adding calorie control and physical activity to the Mediterranean diet prevented around three out of every 100 people from developing diabetes—a clear, measurable benefit for public health.”
The Mediterranean diet focuses on plant-based foods and whole grains, according to the Cleveland Clinic. You’ll also find a lot of healthy fats included, like olive oil, and fish rich in omega-3 fatty acids, such as salmon. The diet limits eating red meat, butter, and sweets.
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