Mediterranean diets and metabolic syndrome status in the PREDIMED randomized trial

Babio N, Toledo E, Estruch R, for the PREDIMED Study Investigators
CMAJ. 2014 Oct 14. pii: cmaj.140764. [Epub ahead of print]        

Background

Lifestyle modifications, such as increased physical activity [1], adherence to a healthy diet [2,3], or weight loss [4-6] are associated with reversion of the metabolic syndrome and its components. It is however unclear whether changes in the overall dietary pattern, without weight loss, might also be effective in improving the condition.
The Mediterranean diet is known to beneficially affect CV disease and related conditions such as diabetes, hypertension and metabolic syndrome. In previous studies that showed a beneficial effect of the Mediterranean diet on metabolic syndrome, it could not be distinguished whether the effect could be attributed to weight loss or to the diet.
Previous analyses of PREDIMED (PREvención con DIeta MEDiterránea) study already suggested that adherence to a Mediterranean diet supplemented with nuts reversed metabolic syndrome more so than advice to follow a low-fat diet [7]. These analyses were however based on 1224 participants followed for one year. The current analysis explores that relationship in the final PREDIMED cohort after a median follow-up of 4.8 years. Participants were randomised to one of 3 nutrition interventions (Mediterranean diet supplemented with either extra-virgin olive oil (EVOO)(n=2543) or with nuts (n=2454), or advised to follow a low-fat diet n=2450).  

Main results

• After follow-up, a significantly smaller increase in prevalence of metabolic syndrome was seen among participants randomised to the EVOO-supplemented Mediterranean diet than in the control-dietary advise group (P=0.013).
• Metabolic syndrome incidence did not differ significantly between the Mediterranean diet groups and the control group, neither did the components of metabolic syndrome show between-group differences.
• When looking only at those participants who met criteria for metabolic syndrome at baseline (n=3392 with complete data), reversion of metabolic syndrome was seen in 958 (28.2%) participants. This was significantly more likely with both Mediterranean diets (control vs. EVOO: HR: 1.35, 95%CI: 1.15-1.58, P<0.001, control vs. nuts: HR: 1.28, 95%CI: 1.08-1.51, P<0.001).
• Participants assigned to the Mediterranean diets were more likely to no longer fulfil the central obesity criterion as compared with the control group, even after adjustment for confounders. The criterion of high fasting plasma glucose was only significantly less often met in the group supplemented with EVOO, as compared to the control group.

Conclusion

This analysis of longer-term follow-up data shows that following a Mediterranean diet supplemented with extra-virgin olive oil is associated with less increase in the prevalence of metabolic syndrome as compared with receiving dietary advice on a low-fat diet. No difference was seen between the diets on new-onset metabolic syndrome, thus the smaller increase of prevalence was likely the result of reversion of the metabolic syndrome. Indeed, fewer participants assigned to the Mediterranean diet met criteria for central obesity and high fasting plasma glucose (only EVOO-supplemented). No differences were seen between weight loss or energy expenditure, thus the change appears to be attributed to the difference in dietary patterns. Thus, the Mediterranean diet may be useful to reduce central obesity and hyperglycaemia in patients with high CVD risk.

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