se Intolerance
In order to understand the physiology behind primary LI,
we must examine what happens to lactase activity as childhood
proceeds. We mentioned before that lactase levels remain high
during infancy. However, what happens after infancy is determined by ones genetic makeup. If one possesses the more
common autosomal recessive gene, lactase activity begins to
drop between the ages of 2 and 20 years(3,4). On the other
hand (or chromosome), if one possesses the less common autosomal dominant gene, lactase activity remains high into adulthood.
What does this mean to those of us sitting in this room?
How many of you can drink milk right now and be free of any
problems? Raise your hands. Do those of you with your hands
raised realize that you are mutants? When I told my sons they
were mutants, they had visions of Ninja Turtles and X-Men,
but I had to clarify that they dont get to live in the sewers or
chase bad guys. Why are you mutants?
No mammal other than man has the ability to ingest milk
as an adult. Even then, only a small percentage of the worlds
humans are actually lactase persistent, as those of you who
raised your hands are known. As many as 75 percent of humans are not able to drink milk as adults without experiencing embarrassing and painful symptoms. Why did some population groups develop the mutation that allowed them to drink
milk as adults? For one possible answer, we turn to simple
Darwinian evolutionary theory.
http://archive.ajpe.org/legacy/pdfs/aj640216.pdf
So depending on the source its anywhere between 75% and 90% of humans are "lactose intolerant"..which makes you the odd ball if you can drink it with absolutely ZERO issues with it...
Also though cheese and yogurt are more tolerable because they are fermented.So some may be able to tolerate those ..while they can not tolerate drinking milk.