The Spanish PREDIMED trial is being considered “landmark” due to its demonstrated dramatic reduction in the risk of a major cardiovascular event by an impressive 30%. The study took place from 2003–2011 and included three groups of volunteers each given a different diet: two with variations of the Mediterranean diet and one simply given a low-fat diet based on the American Heart Association (AHA) guidelines.
The AHA low-fat group was so clearly at a disadvantage for cardiovascular health protection and risk of stroke reduction (which was reduced a significant 49% for those in the Mediterranean diet groups).
The key to cardiovascular benefits so talked about with the Mediterranean diet is the type of fat consumed, not how much: Eat more fat from unrefined plant sources as opposed to saturated fat from animal sources.
The most clear evidence pointed to the plant-based phytonutrients found in unrefined fats from such foods as olive oil and a variety of nuts. While these foods provided the potential benefits, researchers were careful to note that simply adding in a few healthy foods to an already unhealthy diet would make little difference to benefit health; they asserted that whole dietary pattern changes were necessary to provide real results.
Estruch et al. (2013). Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. The New England Journal of Medicine