Key Points

The study was published on 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," added Co-author Frank Hu.

Prior research has linked the Mediterranean diet, which emphasises 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 randomised 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 approximately 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 individuals in the intervention group had a 31% lower risk of developing type 2 diabetes (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 centimetres, compared to 0.6 kilograms and 0.3 centimetres 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 Martinez-Gonzalez, 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.

- ANI