A Mediterranean-style diet, combined with reduced caloric intake, moderate physical activity, and professional weight-loss support, may lower 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 findings were published on August 25, 2025, in the Annals of Internal Medicine.
Global Health Implications
“We’re facing a global epidemic of diabetes,” said Frank Hu, Fredrick J. Stare Professor of Nutrition and Epidemiology and Chair of the Department of Nutrition at Harvard Chan School. He added, “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.”
Why the Mediterranean Diet Matters
As reported by sciencedaily, earlier studies have already linked the Mediterranean diet to better health outcomes. The diet is rich in fruits, vegetables, whole grains, and healthy fats. It also includes moderate dairy and lean protein intake, with minimal red meat. The diet improves insulin sensitivity, reduces inflammation, and lowers the risk of T2D.
Study Design and Participants
To expand on this knowledge, researchers from 23 universities in Spain and Harvard Chan School collaborated on the PREDIMED-Plus clinical trial, the largest nutrition and lifestyle randomized trial in Europe. They enrolled 4,746 participants aged 55 to 75 who were overweight or obese, had metabolic syndrome, but were free of T2D at baseline.
Participants were divided into two groups:
- Intervention group: Followed a calorie-restricted Mediterranean diet (about 600 calories less per day), engaged in moderate physical activity such as brisk walking and strength/balance exercises, and received professional weight-loss support.
- Control group: Followed a Mediterranean diet without calorie restriction, exercise guidance, or professional support.
Key Findings
Over six years, the intervention group showed remarkable benefits:
- 31% lower risk of developing T2D compared to the control group.
- Average weight loss of 3.3 kilograms versus 0.6 kilograms in the control group.
- Reduced waist circumference by 3.6 centimeters versus 0.3 centimeters in the control group.
Public Health Benefits
“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 Miguel Martínez-González, professor at the University of Navarra and adjunct professor of nutrition at Harvard Chan School.