Is Nutrition Really the Key to Good Health?

Having recently returned from Madrid, I confess that I saw little evidence of the Mediterranean diet being consumed there (apart, that is, from the red wine): though, of course, Madrid is in the middle of the peninsula, far from the Mediterranean. Perhaps things are different on the coast. Nevertheless, at over 80 years, Spain has one of the highest life expectancies in the world.

Is this because of the much-vaunted Mediterranean diet? Spanish research recently reported in the New England Journal of Medicine provides some – but not very much – support for the healthiness of that diet.

The researchers divided 7000 people aged between 55 and 80 at risk of heart attack or stroke because they smoked or had type 2 diabetes into three dietary groups. One group (the control) was given dietary advice concerning what they should eat; the two other two groups were cajoled by intensive training sessions into eating a Mediterranean diet, supplemented respectively by extra olive oil or nuts, supplied to them free of charge.

They were then followed up for nearly five years, to find which group suffered from the most (or the least) heart attacks and strokes. The authors, of whom there were 18, concluded:

Among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the incidence of major cardiovascular events.

The authors found that the diets reduced the risk of the subjects suffering a heart attack or stroke by about 30 percent. Put another way, 3 cardiovascular events were prevented by the diet per thousand patient years. You could put it yet another way, though the authors chose not to do so: 100 people would have to have stuck to the diet for 10 years for three of them to avoid a stroke or a heart attack. This result was statistically significant, which is to say that it was unlikely to have come about by chance alone, but was it significant in any other way?

Such significance is in the eye of the beholder, or rather in the opinion of the patient. There are reasons for liking the Mediterranean diet other than health reasons, namely aesthetic ones; and this is important, because if it were discovered that a diet of raw cabbage and boiled fish without salt produced the same result, would anyone other than a masochist contemplate adhering to it? After all, only hypochondriacs turn their meals into medicines and nothing else.

Even if the study had found much more dramatic results than it did find, it would have been severely limited in its application. It does not follow from the fact that the diet prevents stroke or heart attack in people at relatively high risk of having one in the first place that it would prevent either or both of them in people at much lower risk.

On the other hand, it is also possible that the Mediterranean diet would have prevented the development of the high risk in the first place if taken early enough in life. It is true that Mediterraneans, on the whole, have fewer heart attacks and strokes than people of more northerly climes; what is not so clear is how far Mediterraneans actually consume a Mediterranean diet. The idea that diet is the sovereign way to health is a very old one, but given the fact that nations of the most diverse dietary habits are among those with the highest life expectancy, it might not be correct.

In any case, the Spanish research involved the monitoring and one might almost say the badgering of patients to get them to comply with the diet. What is found in the context of a trial is not necessarily transferable to “real” life.
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