Why Is The Mediterranean Diet So Healthy? Study Lets Us Count The Ways

For some of us, the more we understand about why we need to do something, the likelier we are to do it.

So if you already know you'll soon resolve to eat a healthier diet — in particular, the much-vaunted Mediterranean diet — a new study that helps explain its health benefits might add some impetus.

I spoke with senior author Dr. Samia Mora, a cardiologist at Brigham and Women's Hospital and associate professor at Harvard Medical School, and have lightly edited our conversation below.

What did you set out to find?

We set out to see whether women who were eating a Mediterranean-type diet in the U.S. had reduced risk of vascular events over a long-term period, which was about 12 years. And if so, how can that be?

And what did you find?

We found that women who were more closely following a Mediterranean-type dietary pattern were indeed at reduced risk for cardiovascular events over about 12 years. They had about a 25 percent reduction in heart attack and stroke and vascular death.

And that we could explain a lot of that benefit by looking at inflammatory bio-markers that were improved, as well as bio-markers related to glucose and insulin resistance, as well as body adiposity.

There were also some other beneficial effects on blood pressure and lipids and some other metabolites that also contributed to that benefit.

I would have expected more than 25 percent....

Actually, 25 percent improvement is similar to what people find for medications that people use for preventing cardiovascular disease, such as statins, which are commonly prescribed, and it's even greater than what's seen for aspirin. The benefit from a Mediterranean diet has ranged anywhere from about 10 percent up to about 40 percent, depending on the studies.

Your study included about 26,000 women. Is there any reason to think findings in men would be different?

There's no reason to think that, based on the prior data from studies that included both men and women.

If I were your patient, how would you explain to me why the Mediterranean diet is good for my body?

Well, the best news is that it's a combination of different foods that you would be eating. It's really a lot of fruits and vegetables and nuts and legumes and olive oil, and decreasing your amount of red meat and saturated fat and simple sugars. So the health benefits are actually very varied.

As we found in our study, there are many pathways that it affects. We, of course, did not study all the pathways out there. So there are probably additional pathways that could also be contributing.

But we know inflammation had a big effect, and many people suffer from inflammation, and inflammation has a strong risk with vascular events. We also found improvements in insulin resistance — in the way the body metabolizes the glucose, the sugars, that we eat. That was really improved as well.

And even the weight. Some people think, Oh, if I follow the Mediterranean diet, will my weight increase? In fact, the body mass index was lower, and that's actually what's also been found in some other studies, that it is also improved by the Mediterranean diet.

Also, it affected blood pressure, and even cholesterol — in particular for HDL, which is supposedly the good cholesterol, as well as reducing the triglycerides. So there were these many ways that it contributed.

And what we know from other studies is that even a two-point difference in adherence to the Mediterranean diet on a 15-point scale leads to a substantial improvement in reducing cardiovascular events.

At the end of the paper, though, you seem to be saying there's still some mystery about how the diet affects our bodies.

Yes. We did not examine all the potential pathways out there. We examined many of the leading pathways that we know can be related to cardiovascular disease.

But there are other pathways — for example, the Mediterranean diet also has been shown to have anti-arrhythmic properties, preventing people from having heart arrhythmia, which we did not really have a good measure of in our study. We didn't have a really good measure of other pathways, such as vascular function — how healthy the blood vessels in our bodies are.

So we weren't able to measure everything out there; we had measurements for quite a few different pathways but there could be new novel pathways out there as well.

But I think the take-home point is that even small changes in these things, which may not be clinically even noticeable from day to day or from year to year, can cumulatively, in a multi-factorial fashion, really contribute to the benefit over the long term.

So even if I don't lose weight today or tomorrow with having a more Mediterranean-type diet, it is still benefiting me. So I can't focus on necessarily my weight changing or my blood pressure changing from day to day, because these small effects can have cumulative effects in the really long term.

Is it clear which elements of the diet matter most?

In fact, we still don't know which particular element of the Mediterranean diet help more than others. So people can choose from the vegetables, fruits, legumes, nuts, olive oil — especially the extra virgin olive oil — and from other other things as well, such as increasing their fish intake, decreasing the red meat and the saturated fats and the simple sugars and processed foods. You have a variety of foods that you can mix and match and still have benefit from them.