A Mediterranean-style diet, combined with reduced caloric intake, moderate exercise, and professional weight loss support, may lower the risk of developing type 2 diabetes (T2D) by 31%, according to a new study co-led by researchers at Harvard T.H. Chan School of Public Health.
The study is set to be published on August 25, 2025, in the Annals of Internal Medicine.
“Diabetes is a global epidemic. Our study provides high-level evidence that modest, sustained changes in diet and lifestyle could prevent millions of cases worldwide,” said Frank Hu, Fredrick J. Stare Professor of Nutrition and Epidemiology and chair of the Department of Nutrition at Harvard Chan School.
Previous research has shown that the Mediterranean diet—which emphasizes fruits, vegetables, whole grains, healthy fats, moderate dairy and lean proteins, and minimal red meat—supports better health outcomes, including improved insulin sensitivity and reduced inflammation, thereby lowering T2D risk.
To explore whether the diet’s benefits could be amplified with additional lifestyle modifications, researchers from the PREDIMED-Plus trial—the largest nutrition and lifestyle randomized trial in Europe—examined 4,746 participants over six years. The participants, aged 55 to 75, were overweight or obese, had metabolic syndrome, but were free of T2D at the study’s start.
The intervention group followed a Mediterranean diet while also reducing daily caloric intake by approximately 600 calories, engaging in moderate physical activity such as brisk walking and strength exercises, and receiving professional weight loss support. The control group maintained a Mediterranean diet without caloric restriction, exercise guidance, or professional support.
Results showed that the intervention group had a 31% lower risk of developing T2D compared with the control group. They also lost an average of 3.3 kilograms and reduced waist circumference by 3.6 centimeters, compared with 0.6 kilograms and 0.3 centimeters in the control group.
“In practical terms, combining calorie control and physical activity with a Mediterranean diet prevented about three out of every 100 participants from developing diabetes—a clear, measurable public health benefit,” 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.
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