Effect of a Mediterranean Diet Supplemented with Nuts on Metabolic Syndrome Status (PREDIMED)

This 1-year PREDIMED sub-study randomized 1,224 high-cardiovascular-risk adults with metabolic syndrome prevalence of 61.4% at baseline to three dietary interventions: Mediterranean diet supplemented with mixed nuts, Mediterranean diet supplemented with extra-virgin olive oil, or low-fat dietary advice as control.

The Mediterranean diet plus nuts arm reduced metabolic syndrome prevalence by 13.7 percentage points (adjusted OR for metabolic syndrome reversion 1.7 vs. control), while the Mediterranean diet plus olive oil arm reduced it by 6.7 points (not statistically significant versus control). The control arm had only a 2.0% reduction. These metabolic syndrome improvements were achieved without caloric restriction or mandatory weight loss goals.

Metabolic syndrome is a cluster of cardiovascular risk factors (elevated waist circumference, high triglycerides, low HDL-C, elevated blood pressure, elevated fasting glucose) that frequently co-occur in patients with insulin resistance and strongly predicts future cardiovascular events. Reducing metabolic syndrome prevalence through dietary pattern — without drugs — is a meaningful prevention strategy.

The nut-supplemented Mediterranean diet’s superiority over olive oil supplementation suggests that the bioactive components in nuts (polyunsaturated fats, plant sterols, arginine, fiber) contribute independently beyond olive oil polyphenols. These are observational differences between two active dietary interventions, and further mechanistic attribution requires caution.

We rate the evidence strong. A well-designed PREDIMED sub-study demonstrating that Mediterranean diet with nuts substantially reverses metabolic syndrome without calorie restriction — important evidence for dietary pattern as cardiovascular risk intervention.