Thank you to Dr. Moehring for this thoughtful email, and for providing more information on lactose intolerance. We greatly value feedback from our members and online audiences, and are encouraged by the discourse the article, "Today's Paleo Diet" has inspired.
Dear Dr. Garneau:
As a physician I would like to make a brief comment re lactose tolerance in humans following your article on the Paleo Diet. Tolerance of milk beyond the lactation period and early childhood is mainly present in Caucasians, especially in North and Central Europeans and their descendants and people in North India. Most African and Asian races have lactose intolerance of various degrees due to a rapid decline in lactase production after weaning. The continuous expression of the lactase gene may not only be genetically determined, but also due to the continuous consumption of cows milk (or other mammalian milk) among Caucasians. If no milk is consumed after lactation, there is no substrate for lactase, hence the promoter region of the lactase gene is no longer activated. I do not know whether this status is reversible with gradual re-introduction of milk.
I am an (retired) allergist and is often confronted with the differential diagnosis of milk allergy vs. milk (lactose) intolerance.
Although lactose intolerance is reportedly the rule in adult Blacks and Asians I find it fascinating that so many tribes in Subsaharan Africa and people in the steppes of Central Asia (i.e. Mongolians) engage in animal husbandry, especially raising cattle (or buffalo and yaks, etc.). Although this is primarily done I presume for the meat, the milk is consumed, although usually processed as yogurt, cheese or kefir in which the lactose is turned into lactic acid, at least partially.
Roswitha Moehring, M.D.