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Mediterranean Diet Prevents Heart Disease in Those at High Risk

Posted Feb 26 2013 3:00am
Before getting to the good stuff today, let's remind ourselves about the difference between observational studies (in all their various guises) and randomized controlled trials .  The former can only assist in developing hypotheses; they can only make associations & demonstrate links.  They're the medical version of hearsay evidence (in my non-legal mind).  Contrast that w/RCTs which actually demonstrate cause & effect, which is what any good prosecutor or district attorney wants to do, prove that the defendant committed the crime beyond a shadow of a doubt.  At the conclusion of the trial, there should be no doubt in the jury's minds that perhaps the defendant was just in the wrong place at the wrong time.

Along those lines, all prior evidence regarding the benefit of the Mediterranean diet has been observational in nature.  We monitor a bunch of folks as to what they claim to eat and see what happens to them after some given period of time.  We may ask them at the start how they eat (prospective observational study) or at the end (retrospective observational study).  We can look specifically for a cohort of those cases who eat a Mediterranean diet and then compare them to controls, those who are similar in every way except nutrition to the cases.  

But no matter how fancy the statistics, in the end, these studies only demonstrate support of the idea that eating a Mediterranean diet is good for your heart.  It doesn't matter how many of these studies are published, how many participants are involved, how long the studies last, none of these observational studies prove that Mediterranean diet prevents heart disease (the Lyon Diet Heart Study did demonstrate benefit in those w/known heart disease but that's secondary prevention).

Until yesterday, when a randomized controlled study was published in the New England Journal of Medicine in which the authors demonstrated that a Mediterranean diet supplement with either extra-virgin olive oil or with mixed nuts lowered risk for cardiovascular events compared to those who consumed a control diet (basically advised to reduce fat intake).

The authors found 7,447 participants (55-80yo of whom 57% were female) who were at high risk for but had no evidence of cardiovascular disease at study onset and randomized them to either a control diet (advised to reduce fat intake) or to Mediterranean diet supplemented by either extra-virgin olive oil or mixed nuts.  Due to the dramatic reduction in heart attacks, strokes & death from cardiovascular causes, the trial was stopped early after just under 5yrs.
So here's a reasonable RCT demonstrating cause & effect, that eating a Mediterranean diet supplemented with either extra-virgin olive oil or mixed nuts can prevent heart disease in those at high risk but w/o actual known disease.  Let's all start eating this way!  But wait, what is this Mediterranean diet?  Besides the high intake of olive oil, it's also high in fruit, nuts, vegetables & cereals; moderate in fish & poultry; and low in dairy products, red meat, processed meats & sweets.  The oenophiles will love this part: wine is consumed in moderation with all meals!

Is this the end of the story?  No, because it's the first of its kind.  Furthermore, it was performed on a group at high risk for heart disease.  Would it work for those at lower risk?  And as the study was of Spanish nationals, would the results be generalizable to non-Spanish men & women.  And what of the age group?  Would this diet work in a younger cohort?  After all, why wait until middle age to start eating in a health fashion?  So while we now have proof of cause & effect that the Mediterranean diet can prevent heart disease in middle-age Spanish men & women, we've only touched the tip of the iceberg.  We now have to explore all that exists under the water.
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