Do Mediterranean Diets Prevent Type 2 Diabetes?

Jamaluddin Moloo, MD, MPH reviewing Salas-Salvadó J et al. Ann Intern 
Med 2014 Jan 7.
A Mediterranean diet supplemented with extra-virgin olive oil was 
associated with 40% reduction in risk for diabetes.

Weight loss through calorie-restricted diets and exercise lowers risk 
for type 2 diabetes. To assess whether Mediterranean diets without 
caloric restriction also protect against diabetes, researchers in 
Spain analyzed data on the 3500 nondiabetic participants in the 
PREDIMED prevention trial (NEJM JW Gen Med Mar 12 2013http://
www.jwatch.org/jw201303120000001), in which adults with ≥3 
cardiovascular risk factors were randomized to one of three diets: a 
Mediterranean diet supplemented with extra-virgin olive oil (EVOO; 3–
4 tablespoons daily), a Mediterranean diet supplemented with mixed 
nuts (1 ounce daily), or a control diet (consisting of advice to 
reduce intake of all fats). No participants were advised to restrict 
calories or to increase physical activity.

During median follow-up of 4 years, 273 participants developed 
diabetes. Incidence rates were 16, 19, and 24 cases per 1000 person-
years, respectively, in the EVOO group, the nut-supplement group, and 
the control group. After adjustment for potential confounders, the 
hazard ratios for diabetes were significantly lower for the EVOO group 
(0.60) and slightly but not significantly lower for the nut group 
(0.82) relative to controls. No significant changes occurred in 
weight, waist circumference, or physical activity levels across groups.

COMMENT

In this study, a Mediterranean diet supplemented with extra-virgin 
olive oil lowered diabetes incidence without associated weight loss or 
increased physical activity. The mechanism by which a Mediterranean 
diet might lower diabetes risk is unknown, but, as the authors note, 
such diets might alleviate inflammation, oxidative stress, and insulin 
resistance.

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