Primary Prevention of Cardiovascular Disease with a Mediterranean Diet, New England Journal of Medicine, 25 February 2013
7447 people "with no cardiovascular disease at enrollment" were randomly assigned to one of 3 diets. After ~4.8 years into the study:
- 96 people assigned to the Mediterranean diet plus olive oil (about 4 tablespoons/day) group experienced a major cardiovascular event.
- 83 people assigned to the Mediterranean diet plus nuts (about 1 ounce/day mixed - 15 g walnuts, 7.5 g almonds, 7.5 g hazelnuts) group experienced a major cardiovascular event.
- 109 people assigned to the control diet (advised to reduce fat but didn't) experienced a major cardiovascular event.
Why did 179 people who had no cardiovascular disease (CVD) prior to entry into this study experience heart attacks or strokes after eating a Mediterranean diet supplemented with olive oil or nuts? It sounds like what they were doing before they started supplementing their diets with olive oil and nuts protected them more from CVD, since they apparently developed it only after partaking in the study.
Dr. Esselstyn had much better success with his plant-based, oil-free diet and his patients did have CVD:
"The patients in Dr. Esselstyn’s initial study came to him with advanced coronary artery disease. Despite the aggressive treatment they received, among them bypasses and angioplasties, 5 of the original group were told by their cardiologists they had less than a year to live. Within months on Dr. Esselstyn’s program, their cholesterol levels, angina symptoms, and blood flow improved dramatically. Twelve years later 17 compliant patients had no further cardiac events. Adherent patients survived beyond twenty years free of symptoms."Back to the present study ... There was a 30% reduction in risk (of a "major cardiovascular event" but only stroke reached significance) for eating the Mediterranean diet, but this article from the New York Times said:
"Those assigned to a low-fat diet did not lower their fat intake very much. So the study wound up comparing the usual modern diet, with its regular consumption of red meat, sodas and commercial baked goods, with a diet that shunned all that."The authors said so much:
"We acknowledge that, even though participants in the control group received advice to reduce fat intake, changes in total fat were small."Perhaps the benefit was due to eliminating red meat, soda, commercial baked goods, and dairy (the control group was advised to consume 3 or more servings of dairy a day, the Mediterranean diet groups were not) and not due to eating olive oil or nuts. It's hard to say since the authors did not divulge what participants in each group ended up eating. (Update: I was wrong about this. I just reviewed the supplemental materials. Here are some additional facts:
- The control group, which had been advised to eat a low-fat diet, was eating 37% of their calories from fat. The low-fat diet community says a low-fat diet gets 10-12% of its calories from fat. The American Heart Association says a low-fat diet is <30% fat. By any standard, this was not a low-fat diet.
- Both Mediterranean diet groups ate more vegetables, fruits, legumes, wine, and seafood than the control group. (Table S5, p<0.05).
- The Mediterranean diet groups did not reduce risk for heart attack, death from cardiovascular causes, or death from any cause. "Only the comparisons of stroke risk reached statistical significance."
Given Esselstyn's scorecard, people eating the Mediterranean diets in this study could have reduced their CVD risk further by reducing intake of processed fats (including olive oil) and nuts.
This study was conceived and conducted in Spain. The olive oil and nuts given to participants were supplied by producers in Spain, who were probably very happy to see the results lauding oil and nuts' benefits published in a prestigious journal. Also, the authors of this study report the following conflicts of interest:
- Research Foundation on Wine and Nutrition
- Beer and Health Foundation
- European Foundation for Alcohol Research
- California Walnut Commission
- International Nut and Dried Fruit Council
- Mediterranean Diet Foundation