27 February 2013

Are Diet Benefits Transethnic?

A recently published study of 7,000 people in Spain found great health benefits for a Mediterranean diet.

A group of men and women, ages 55 to 80 at the start of the study, were randomly assigned to a low-fat diet or one of two variations of the Mediterranean diet: one featuring a lot of extra-virgin olive oil (more than a quarter cup a day) and the other including lots of nuts (more than an ounce a day of walnuts, almonds and hazelnuts). . . . Overall, the people consuming the diets rich in olive oil or nuts had about a 30 percent lower risk of having a heart attack, stroke or dying from a cardiovascular cause. In absolute terms, there were about 8 of those problems for every 1,000 person-years in the Mediterranean diet groups compared with 11 per 1,000 person-years in the low-fat diet group.
Clearly, for people of Mediterranean ancestry, a Mediterranean diet improves health relative to a low-fat diet, which has its roots in modern nutrition theory in the observation that many Asian countries with low rates of cardovascular diseases had diets very low in fat and high in carbohydrates. 

But, does a Mediterranean diet work equally well for non-Mediterraneans?

I have yet to see a study that really firmly establishes that people of all ancestries benefit equally from a Mediterranean diet or any other particular kind of diet.  American studies rarely break out their subjects at a sufficiently fine grained level to know, and since many Americans have significant Southern European ancestry (including many Hispanics), if a Mediterranean diet is particularly helpful to them, there would be an improvement in that average health of the study subjects.

My intuition that this might be the case begins with the observation that I personally do not fair well with meals that are high in olive oil.  Even if the quantity of olive oil is no more than an equivalent amount of butter that I would have no trouble with, too much olive oil can leave me with an upset stomach and the runs (even though I like the taste).  It seems plausible to me that this might have something to do with the fact that my immigrant ancestors who hail from Finland, what is now North Central Germany, and Ireland, where olive oil was rarely used right up to the point that my ancestors emigrated, and where butter and lard were commonly used in cooking up through that point.

At any rate, it is certainly plausible to me that people of European origins to the north of the cultural olive oil-butter line, are less tuned, genetically and in their overall diet mix, to diets rich in olive oil, something rarely available to their ancestors, and more tuned, genetically and in their overall diet mix, to processing the saturated fats that were consumed by their ancestors.  Likewise, it is plausible to me that an optimal diet for someone of East Asian or of West African ancestry might be different from an optimal diet for someone from Southern Europe or the Middle East.

For example, the diet of people in Northern France is very rich in saturated fats, but have surprisingly low levels of health problems given their diet.  One factor known to buffer the harms from their seemingly heart unhealthy diet is a high level of red wine consumption that has an effect similar to statin drugs or low dose asprin regimes in reducing cardiovascular problems associated with bad cholesterol.  But, it wouldn't surprise me at all if people in that region also had genetic adaptations that made their bodies better tuned to the regional diet.

Gense that affect how our bodies process foods that are abundant in an area, and genes that impact mortality risks from diseases that are present in an area are almost never selectively neutral.

Now, some foods, like large quantities of highly refined sugars, were not widely available to almost anyone until the last century or two.  So, it would be no surprise if these foods are unhealthy for almost everyone.  But, that doesn't necessarily mean that all people in a multiethnic society will benefit to an equal extent from any particular diet.

Ethnic differences in diet benefits could also have something to do with the intersection of cultural background and diet compliance.  It is much easier to keep to a vegetarian diet if you are a Hindu from India who knows many recipes for vegetarian dishes and for whom "home cooking" and "comfort food" rarely involves meat, than it is if you grew up in a Texas ranching community where beef and pork were a part of your diet in almost every single meal and you've never eaten lentils or an eggplant or tofu in your entire life.  Even if the bodies of the Texan and the Hindu process vegetarian meals identically, the Texan is going to find it much more difficult to stick to a vegetarian diet than the Hindu will.

Comments pointing out any research on this issuse are welcome.

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