Source: de Lorgeril M, Salen P, Martin, J, et.al. Mediterranean Dietary Pattern in a Randomized Trial. Archives of Internal Medicine 1998, 158: 1181-7.
de Lorgeril M, Renaud S, Mamelle N, et al. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. The Lancet; Jun 11, 1994; 343:1454-9.
Efficacy Endpoints: Overall survival, new cancers, heart attack
Harm Endpoints: None
Narrative: Background: The Mediterranean population is known to have a lower incidence of coronary heart disease compared to other groups.1 It is unclear what the reason for this is, speculation is mostly dietary and includes the protective effects of olive oil (linoleic acid) or flavonoids in red wine, the heavy reliance on fruits and vegetables, and the relative paucity of dairy and red meat. The “typical” Mediterranean diet:
Mediterranean diets are low in saturated and omega-6 fats, but high in omega-3 fats, oleic acids, fiber, antioxidants, vegetable proteins, and B vitamins.
Study Descriptions: In this single blinded secondary prevention trial 605 survivors (10% female) of a first acute myocardial infarction were randomized to the American Heart Association Step 1 diet or to a Mediterranean-type diet for 5 years. Patients randomized to the Mediterranean-type diet were given free quantities of a rapeseed oil-based margarine. Rapeseed oil is similar in composition to olive oil, though it is composed of slightly higher amounts of linolenic acids.
The study was terminated early due to significant benefit found at intermediate analysis at ~4 years. Death occurred in 34/303 (8.0%) in the control group versus 14/302 (4.6%) in the Mediterranean diet group (p=0.03). There were new cancers discovered in 17/302 (5.6%) of the control group versus 7/302 (2.3%) in the Mediterranean diet group (p=0.05). There were 33 (8.2%) non-fatal MI’s in the control group versus 8 (2.6%) in the Mediterranean diet group.
Patients who developed cancer in both groups had much higher rates of smoking. There were no significant differences in the 2 groups in terms of tobacco use, medications used (including anti-lipids), exercise, weight, blood pressure, and psychosocial factors that were addressed in a separate paper.2 The only significant difference found between the control and experimental groups was in nutrient intake. Interestingly, there was no significant difference between the groups in terms of serum cholesterol, triglycerides, or HDL at the end of the study.
Caveats: It is not certain to what degree each diet was followed in each group, though surveys and serum samples of the experimental group point to strong Mediterranean diet adherence. The authors specifically tried to evaluate for a placebo effect from the diet counseling via surveys and concluded there was none. The fact that the patients were 90% male makes it harder to draw conclusions about the possible impact of diet in women.
The magnitude of this study’s results is astonishing. To compare saving a life post-heart attack with this diet (NNT= 30) and with statins (NNT=83) suggests that diet is nearly three times more powerful as a life-saving tool. A few factors make this particularly remarkable. Cancers were also reduced, while some authors have raised concerns about statins increasing cancer risk (without supporting evidence in the industry-sponsored trials to date). Imagine that the control group had been following a typical dietary pattern rather than the AHA recommended diet; the size of the effect could be even greater. Finally, the study suggests that cholesterol, which was not reduced by the Mediterranean diet, may not be as important a dietary consideration for heart disease prevention as currently thought and practiced.
It is difficult to make sweeping statements from a single study, but given the existing data and lack of harms the Mediterranean diet seems beneficial and should be strongly recommended at this time.
Author: Joshua Quaas, MD
Published/Updated: September 17, 2010
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