Timing is everything, they say.
Let s review what happens when someone with LI drinks a glass of milk as part of a meal. This takes about an hour on average. A liquid, such as milk, may move through faster, since an individual milk drop is already small, but nothing much happens immediately. In the second part of the small intestine, a place called the jejunum, the milk washes over the cells that manufacture lactase, the enzyme that digests lactose. Even those people with LI usually have some lactase activity, just not enough to make a difference.