Map of life expectancy at birth from Global Education Project.

Tuesday, February 26, 2013

Yes, this really is a breakthrough study

You may have seen coverage of this in the corporate media, but I'm going to give you a bit of value added. A randomized controlled trial finds that the so-called Mediterranean diet results in fewer strokes and heart attacks, not to mention fewer deaths, in people at high risk for heart disease.

Now here's why this is a big deal. Most of what we know about nutrition and health comes from observational studies. It's very difficult to sort out the effects of nutrition on human health because, among other problems:

  • People's diets are obviously very complex. You can't easily or convincingly sort out the effect of one dietary component or characteristic from all the other features of diet;
  • People's diets tend to be correlated with all sorts of other facts about them, including socio-economic status, where they live which is associated with all sorts of other exposures, their culture, their consumption of health care and all sorts of health-related behaviors from smoking to physical activity to how often they have sex;
  • There is confounding by indication. People who are overweight, or diabetic, or otherwise have been told by their doctors that they are at risk or believe they are for whatever reason may already be trying to modify their diets.
  • Doing long-term, randomized controlled trials is extremely difficult because people don't stick to the diets they are assigned.
These Spanish investigators overcame these problems by, first of all, deliberately selecting people who are at high risk -- who have been diagnosed with diabetes or overweight, with a median age of 67 years. They included smokers, and people who are taking medications for hypertension and cholesterol. They randomly assigned them to a low fat diet group, and two Mediterranean diet groups, one of which got free olive oil and one of which got free nuts in addition to nutritional counseling.

Finding #1: People could not stick to the low fat diet. We already know that: diets are very hard to stick to. So this group ended up being basically a control group of people who eat whatever. BUT, people could stick to the Mediterranean diet group. They got to eat all they wanted -- there was no attempt at calorie control. They were allowed to drink alcohol (encouraged to be in the form of red wine with meals). They didn't have to stop smoking or lose weight or do anything else. This diet is satisfying to eat, and allows all kinds of great tasting food. So unlike all the other diets out there, it's actually possible: you can do it.

Finding #2: No, the people didn't lose weight, but they didn't gain weight either, even though they were actually encouraged to eat a lot of fat, consisting of nuts, olive oil, and fatty fish. What they also didn't do was have as many heart attacks or strokes. The big win was stroke, which was statistically significantly less likely to happen with the Mediterranean diet after three years than the regular diet. That probably drove all of the results, but everything else got at least slightly better or no worse, including death, particularly with the olive oil supplementation, although this didn't hit the arbitrary p<.05 level of significance. Still, who wants a stroke?

So no, we don't know exactly what pieces of this were most important, but it confirms what I've been saying all along. It's not how much fat you eat, it's what kind of fat. Olive oil and nut oils are what you want. Also lots of veggies, legumes, and fish. (Alas, fish are not generally a sustainable food. We'll have to figure something out in that department.)  Skip the red meat and go very easy on the dairy fat. (Some Mediterranean cuisines have more goat cheese than cow cheese, which probably also helps since it's lower in fat.) Tomato sauces with olive oil are jes' fine, as are birds. You can do that!

Sure, you should also quit smoking and maintain a healthy weight and all that, but the news here is, even if you don't do that, you still benefit. Really. It's not a mystery.

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