forestwalker
Bushcrafter (boy, I've got a lot to say!)
We all are born Lactose tolerant.
I was tought 30+ years ago in med school that Lactose intolerance can happen two ways:
1: we stop to drink milk and then lose the production of the enzymatic system, a normal body reaction.
2: we lose the enzymatic system despite drinking milk. This is a pathologic reaction.
I am sure sciense has better understanding, knowledge and explanation today though.
personally I stopped drinking milk and developed the intolerance. I am fine with proper aged cheeses, and small amounts if Lactose free milk, small amounts in my cofee, or in sauces.
There are at lest some reports that it is an inducible enzyme[1,2], but others claim not[3] (i.e. production may be restarted if you start ingesting it, but don't expect it to be instant). I would not be surprised if there is a huge genetic variation here...
[1] http://nutritionreviews.oxfordjournals.org/content/28/5/138
[2] http://onlinelibrary.wiley.com/doi/10.1111/j.1432-1033.1994.tb19969.x/pdf
[3]http://www.efsa.europa.eu/sites/default/files/scientific_output/files/main_documents/1777.pdf