It seems like every time you turn around, you're being told to drink more milk. Yet, roughly one-sixth of the U.S. population, and probably even a higher percentage in our Chihuahuan Desert, is lactose intolerant, and dairy products cause such symptoms as nausea, bloating, gas, and diarrhea. Lactose is milk sugar, and all mammals normally start out being able to split this double sugar into its digestible parts with the enzyme lactase. After all, sugar is a vital energy source in the mother's milk.
On a worldwide basis, most humans drastically reduce the amount of
lactase they produce as they get beyond the age of weaning. Without sufficient amounts
of the enzyme, lactose is no longer digested, and the symptoms of lactose intolerance
appear. Maintenance of the enzyme into adulthood is common only in peoples whose
ancestry included heavy reliance on dairy products: Europe, the Middle East, and India.
As you might expect, talking about the "milk of human kindness" originated in
those regions; for the rest of the world, that equation is badly curdled.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.