Cutting calories on top of a Mediterranean diet lowered diabetes risk by 31%

The Mediterranean diet has a stronger evidence base for cardiovascular outcomes than almost any other dietary pattern. What has been less clear is whether adding the two things most weight-loss programmes add — a calorie deficit and structured physical activity — buys anything further. A prespecified secondary analysis of the Spanish PREDIMED-Plus trial, published on 25 August, provides one answer for type 2 diabetes [s1].

The trial

PREDIMED-Plus is a randomised, single-blinded controlled trial run across 23 centres in Spain [s1]. It enrolled 4,746 adults aged 55 to 75 with metabolic syndrome and overweight or obesity, and without prior cardiovascular disease or diabetes [s1].

Participants were randomised 1:1. The intervention group received an energy-reduced Mediterranean diet with a planned reduction of 600 kcal per day, increased physical activity, and behavioural strategies for weight loss [s1]. The control group received advice to follow a Mediterranean diet ad libitum — the same dietary pattern, without the calorie target, the exercise programme or the behavioural support [s1].

This is the design feature that makes the study informative. Both arms got the Mediterranean diet. The comparison isolates the added ingredients rather than the diet itself.

Diabetes incidence was determined using American Diabetes Association criteria, anthropometric measurements were taken annually, and Cox regression models assessed the intervention effect [s1].

The result

Over a median six years of follow-up, the six-year absolute risk of type 2 diabetes was 12.0% in the control group (349 cases) and 9.5% in the intervention group (280 cases) [s1].

That is a relative reduction of 31% (95% CI, 18% to 41%) and an absolute risk reduction of 2.6 cases per 1,000 person-years (95% CI, 2.4 to 2.7) [s1].

The intervention group also achieved better adherence to the energy-reduced Mediterranean diet, higher physical activity levels, and greater reductions in body weight and waist circumference [s1].

Two ways of reading the same numbers are both fair. The relative figure — a 31% reduction — is the one that will travel. The absolute figure is that roughly 25 people in every 1,000 avoided a diabetes diagnosis over six years, or put differently, about 88% of controls and about 90.5% of the intervention group did not develop diabetes.

What the authors themselves flag

The paper lists three limitations plainly: this was a secondary outcome, the design was single-blinded, and dietary adherence was self-reported [s1].

Each matters. A prespecified secondary outcome carries less inferential weight than a primary one, because a trial powered and designed for a different endpoint is being asked a question it was not built around. Single-blinding means participants knew which arm they were in, which affects behaviour in ways that go beyond the intervention itself. And self-reported dietary adherence is the standing weakness of nutrition trials — people report what they intended to eat.

The trial was funded by Instituto de Salud Carlos III, Spain's national health research institute [s1].

An accompanying editorial published the same day considers what the result means for reducing diabetes risk through the Mediterranean diet [s2].

What it cannot separate

The intervention bundled three things: calorie restriction, physical activity and behavioural support [s1]. The trial cannot say which of them produced the effect, or in what proportion. Given that the intervention group lost more weight and more waist circumference [s1], weight loss is the obvious mediating candidate — but that is inference, not a reported finding.

Nor does the result transfer automatically outside its population. Participants were Spanish adults aged 55 to 75 with metabolic syndrome and overweight or obesity, already at elevated diabetes risk [s1]. In a lower-risk population, the same relative reduction would translate into a much smaller absolute one, because there are fewer events to prevent.

The trial also compared an intensive intervention against advice. Some of the difference reflects intensity of contact and support rather than the specific content of the advice — a limitation shared by nearly every lifestyle trial ever run.

Where it leaves things

The authors' conclusion is careful: an intensive intervention adding caloric reduction, physical activity and modest weight loss to the Mediterranean diet was more effective than ad libitum Mediterranean diet advice alone in reducing diabetes incidence in people with overweight or obesity and metabolic syndrome [s1].

That is a narrower claim than "the Mediterranean diet prevents diabetes," and a more useful one. It says that in a population already at elevated risk, telling people to eat a Mediterranean diet and leaving it there produced worse outcomes over six years than telling them to eat it, cut 600 kcal, move more, and supporting them while they did.

Nothing here is a recommendation for any individual. Diabetes risk, and what to do about it, is a matter for a clinician who knows the person's full history.

Sources

• 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, 2025-08-25
• Reducing Diabetes Risk Through the Mediterranean Diet — Annals of Internal Medicine, 2025-08-25