Milk -To Drink or Not To Drink?

About 70% of the world’s population lacks the ability to produce the enzyme beta-galactosidase, better known as lactase. Without this, lactose, the sugar in milk, cannot be properly digested.

“Lactose intolerance” is most prevalent among people of Asian, African and to a lesser extent, Mediterranian origin. Many parts of the Asian and African continents were once afflicted by sleeping sickness, a disease transmitted by the tsetse fly, that resulted in the destruction of most cattle populations. Geneticists believe that the resulting unavailability of milk in these area led to lactose intolerance. In terms of evolution, such a response would be appropriate, since disruption of the synthesis of a non-required enzyme would be energetically advantageous to the human body. Although lactose intolerance is rare among infants, the ability to produce the enzyme drastically decreases during the years after weaning in predisposed individuals. Even lactose intolerants, however, can usually consume a single glass of milk (about 15 grams of lactose) without the serious ill effects normally associated with the condition, namely diarrhea and abdominal cramps.

The diarrhea is likely the result of increased flow of water into the intestine (through osmosis) in response to lactose buildup. At the same time, fermentation of small amounts of lactose by bacteria commonly found in the digestive tract, results in the production of gases which in turn can lead to cramps. One of the gases produced, hydrogen, is used as an indication of lactose intolerance in a widely applied breath test. Since milk is the most common dietary source of calcium, there has been concern that people suffering from lactose intolerance become calcium deficient and are often given the advice to eat cheese and yogurt instead of drinking milk since these are low in lactose. An ounce of cheddar cheese provides as much calcium as a cup of milk, but less than one tenth as much lactose. Another way to attack the problem is with Lact-Aid, a preparation containing the missing enzyme. A few drops of this solution can be added to milk, leading to the destruction of most of the lactose within 24 hours.