Humans are the only animal that continue to drink milk beyond their infancy (they’re also the only animal that regularly drink milk produced from another animal too, but that’s out of scope of this post). The ability for humans to do this is courtesy of a genetic mutation that has evolved in different herding communities (Europeans, East Africans, and Saudi Arabians) throughput history. Contrary to popular American belief, lactose tolerance is the exception, not the rule, around the world. [See: From Atoms to Traits, Scientific American, January 2009, pg 52; and Evolution of Evolution].
I, however, am of mostly European descent and that the rest of my immediate family retains their lactose tolerance suggests that I too should have retained mine outside of infancy. My lactose tolerance was going strong up until about four or five years ago. Since then I’ve been able to handle milk products in small amounts (milk on my cereal, small glass with cookies, moderate amounts of cheeses) but larger amounts (any amount of ice cream and heaven forbid a bite or two of cheesecake) results in extreme agony unless I pop a lactase (the enzyme needed to break down lactose) pill prior to the consumption.
This inconvenience is just that, an inconvenience. With adequate forethought and preparedness I’m still able to have that scoop of Rocky Road ice cream for dessert.
What’s puzzled me though is why the onset of lactose intolerance occurred at all. It is true that lactose tolerance can dwindle as one ages due to the body’s declining production of lactase — or in other words I’m just getting old. The onset of lactose intolerance after a time when one had a tolerance is also a result of celiac disease – which is an intolerance for gluten: the body’s reaction to gluten results in an inability to break down lactose. Because of this outside possibility I’ve been on a gluten-free diet for the past 1.5 weeks to give it a go.
More details on my gluten-free experience will be forthcoming (the details were originally destined for this post but I kept backtracking to give enough background that we got stuck on lactose instead :).