In their multi-centre, randomised trial in Spain, 7447 high risk patients with no clinical vascular disease (age range 55-80, 57% women) were asked to follow one of 3 dietary options:
- a Mediterranean diet with
- extra-virgin olive oil
- or with mixed nuts
- or a control diet with advice to reduce dietary fat.
The primary end point was rate of major cardiovascular events (myocardial infarction, stroke, or death from cardiovascular causes). The trial was stopped early after median follow-up 4.8 years.
What did they find? After adjusting for obvious bias, both Mediterranean diet groups had significantly better outcomes: hazard ratios compared to the control group (109 clinical events)
- added oil: 0.70 (95% confidence interval [CI], 0.54 to 0.92) - 96 clinical events
- with nuts: 72 (95% CI, 0.54 to 0.96) - 83 clinical events
In other words, the relative risk of serious cardiovascular disease was reduced by one third by following a calorie unrestricted Mediterranean diet vs. a low fat diet. The absolute risk reduction was 3 fewer clinical events for every 1000 patient years of treatment ie ~3 fewer clinical events for every 200 patients following the Mediterranean diet option for 5 years. There were 2-3 future strokes per 1000 patient years of treatment.
Considering the impact of these preventable strokes alone, using UK data as an example, that decrease of 2-3 strokes per 1000 patient years of treatment would represent ~300-450 fewer strokes per year at a saving in direct and indirect health costs, and further societal annual costs of ~£16–25m [€18-28m].
Of note, patients were supported during the study by regular educational prompts, as well as some free food supplements.
These were clearly patients at high risk from cardiovasular disease either from:
- type 2 diabetes mellitus or
- at least three of
- raised bad (LDL) cholesterol
- low good (HDL) cholesterol
- overweight or obesity
- family history of premature coronary heart disease
The authors themselves raise the obvious questions whether people not living in a Mediterranean and/or at lower cardiovascular risk would receive similar benefit.
Their results at least however 'support the benefits of the Mediterranean diet for the primary prevention of cardiovascular disease' in patients already at high risk: an important message for policy makers, health professionals, and at least those with the above risk factors for serious vascular events.
Estruch R, Ros E, Salas-Salvadó J et al: the PREDIMED Study Investigators. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. N Engl J Med. 2013 Feb 25. [Epub ahead of print]