Mediterranean diet combined with calorie reduction and exercise may reduce risk of type 2 diabetes by nearly one-third

Embargoed for release: Monday, August 25, 2025, 5:00 PM ET

Key points:

• Those who adhered to a Mediterranean diet, reduced their caloric intakes, engaged in moderate exercise, and received professional weight loss support had a 31% lower risk of developing type 2 diabetes compared to those who adhered to a Mediterranean diet alone.
• The findings come from PREDIMED-Plus, the largest nutrition and lifestyle clinical trial ever conducted in Europe.

Boston, MA—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.

The study was funded by the European Research Council, the Spanish National Institute of Health, the Biomedical Research Networking Centre (CIBER), and the U.S. National Institute of Diabetes and Digestive and Kidney Diseases (1R01DK127601).

“Comparison of an Energy-Reduced Mediterranean Diet and Physical Activity Versus an Ad Libitum Mediterranean Diet in the Prevention of Type 2 Diabetes,” Miguel Ruiz-Canela, Dolores Corella, Miguel Ángel Martínez-González, Nancy Babio, J. Alfredo Martínez, Luis Forga, Ángel M. Alonso-Gómez, Julia Wärnberg, Jesús Vioque, Dora Romaguera, José López-Miranda, Ramón Estruch, José Manuel Santos-Lozano, Luis Serra-Majem, Aurora Bueno-Cavanillas, Josep A. Tur, Vicente Martín-Sánchez, Antoni Riera-Mestre,  Miguel Delgado-Rodríguez, Pilar Matía-Martín, Josep Vidal, Clotilde Vázquez, Lidia Daimiel, Pilar Buil-Cosiales, Sangeetha Shyam, Jose V. Sorlí, Olga Castañer, Antonio García-Rios, Laura Torres-Collado, Enrique Gómez-Gracia,  M. Ángeles Zulet, Jadwiga Konieczna, Rosa Casas, Naomi Cano-Ibáñez, Lucas Tojal-Sierra, Rosa M. Bernal-López, Estefanía Toledo, Jesús García-Gavilán, Rebeca Fernández-Carrión, Albert Goday, Antonio P. Arenas-Larriva, Sandra González-Palacios, Helmut Schröder, Emilio Ros, Montserrat Fitó, Frank B. Hu, Francisco J. Tinahones, Jordi Salas-Salvadó, the Annals of Internal Medicine, August 25, 2025, doi: 10.7326/ANNALS-25-00388

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Harvard T.H. Chan School of Public Health is a community of innovative scientists, practitioners, educators, and students dedicated to improving health and advancing equity so all people can thrive. We research the many factors influencing health and collaborate widely to translate those insights into policies, programs, and practices that prevent disease and promote well-being for people around the world. We also educate thousands of public health leaders a year through our degree programs, postdoctoral training, fellowships, and continuing education courses. Founded in 1913 as America’s first professional training program in public health, the School continues to have an extraordinary impact in fields ranging from infectious disease to environmental justice to health systems and beyond.