Monday, 4 October 2004
10:41 PM
MSN ran an article today on "What you need to know about lactose intolerance." They represent lactose intolerance as ranging from mild to severe, although they do note that most people can tolerate small amounts. This sent me to my wonderful On Food And Cooking, the masterpiece by Harold MacGee on the science of, um, food and cooking. This is his note on lactose intolerance:It was not until the late 1960s that Western medical science realized that adult lactase deficiency -- the inability to digest milk sugar -- was the rule rather than the exception, and was not really a deficiency at all but the natural state of affairs. It took this long because most Westerners, in particular those of northern European background, are capable of digesting lactose in adulthood. Their lactase levels, and those of a couple of nomadic African tribes, do not drop off as drastically as those of the rest of the world's population. The "ethnic chauvinism," as it has been called, of assuming that everyone could digest milk led to such policies as shipping surplus powdered milk to famine areas where it could do as much harm as good. This attitude was overcome only when the researchers noticed that about 70% of American blacks are intolerant of lactose, while the figure for whites is closer to 10%. A few years of study showed that lactose-tolerant adults are a distinct minority on this planet.
This is not to say that only a minority can eat dairy products. Most lactose-intolerant adults can consume about a pint of milk per day, which provides valuable amounts of several nutrients, without severe symptoms. (This is not true of people who are allergic to milk proteins. Lactose intolerance is not an allergy.) And cheese, yogurt, and other cultured foods are practically free of lactose because the fermenting bacteria use it as fuel. But the practice of dairying would have been unlikely to develop in populations with a low tolerance for milk itself. It has been suggested that the genetic trait of continuing with lactase production arose in the people of northern Europe because it conferred the advantages of increased calcium intake and improved absorption of that mineral (one of the effects of lactose in the small intestine) on a group whose dark, cold environment developed little vitamin D in the skin. Of course, the ability to drink milk also simply widens the range of foods on which people can survive. In any case, lactose tolerance is probably a very recent adaptation. Mother's milk has been drunk on our branch of the phylogenetic bush for millions of years, but sheep, goats, and cows have been milked only for a few thousand.
-- Harold McGee, On Food and Cooking
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