Mediterranean diet combined with calorie reduction and exercise may reduce diabetes risk by nearly one-third: Study

A Mediterranean-style diet, in combination with reduced caloric intake, moderate physical activity, and professional support for weight loss, may cut the risk of type 2 diabetes (T2D) by 31%, according to a new study co-authored by researchers at Harvard T.H. Chan School of Public Health.

The study will be published August 25, 2025, in the Annals of Internal Medicine.

“We’re facing a global epidemic of diabetes,” said co-author Frank Hu, Fredrick J. Stare Professor of Nutrition and Epidemiology and chair of the Department of Nutrition. “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.”

Prior research has linked the Mediterranean diet-which emphasizes high intake of fruits, vegetables, whole grains, and healthy fats, moderate intake of dairy and lean proteins, and little to no intake of red meat-to better health outcomes, including lowered risk of T2D through improved insulin sensitivity and reduced inflammation.

A team of collaborators from the PREDIMED-Plus clinical trial, the largest nutrition and lifestyle randomized trial in Europe, sought to understand how the diet’s benefits may be enhanced with additional healthy lifestyle changes.

The researchers, from 23 universities in Spain and Harvard Chan School, split 4,746 PREDIMED-Plus participants into an intervention group and a control group and followed their health outcomes for six years. The intervention group adhered to a Mediterranean diet; reduced their caloric intake by about 600 calories per day; engaged in moderate physical activity, such as brisk walking and strength and balance exercises; and received professional support for weight loss control. The control group adhered to a Mediterranean diet without calorie restriction, exercise guidance, or professional support. Participants ranged from age 55 to 75, were overweight or obese, and had metabolic syndrome, but were free of T2D at baseline.

The study found that those in the intervention group had a 31% lower risk of developing T2D compared to those in the control group. Additionally, the intervention group lost an average of 3.3 kilograms and reduced their waist circumference by 3.6 centimeters, compared to 0.6 kilograms and 0.3 centimeters in the control group.

“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,” said co-author Miguel Martínez-González, professor at the University of Navarra and adjunct professor of nutrition at Harvard Chan School.

Reference:

Miguel Ruiz-Canela, Dolores Corella, Miguel Ángel Martínez-González, Comparison of an Energy-Reduced Mediterranean Diet and Physical Activity Versus an Ad Libitum Mediterranean Diet in the Prevention of Type 2 Diabetes: A Secondary Analysis of a Randomized Controlled Trial, Annals of Internal Medicine, https://doi.org/10.7326/ANNALS-25-00388