This is rather simple to answer actually. Most people have no problem drinking and digesting milk and dairy products when they are young, usually until they are late teenagers. Then for no explicable reason, a glass of milk or two or a bowl of rich ice cream will cause digestive problems and an upset stomach, may be even worse.
What gives is that most of us humans and animals for that matter are born with a digestive enzime called lactase-phlorizin hydrolase or just LPH or lactase. LPH is the enzyme that digests the lactose sugar in milk. Animals are much smarter than humans. When nature takes its course and makes milk unpalatable for a growing animal it moves on from its mother’s milk to other nutrition more suitable for their age. Humans, not so much. Humans think, “wow, it isn’t cool to suckle my mothers breast any more, but boy I like milk, so I’ll just drink milk from animals to be more PC.”
What happens is that as we grow our bodies don’t need the nutrition that our mother’s milk or animal’s milk might provide in that form, so nature in it’s infinite wisdom reduces the body’s output of lactase. Some people’s output remains higher than others just like some people are bald and some aren’t. It’s kind of like developing “shame” when we leave our 20’s so we don’t hurt ourselves doing stupid things any more.
Bottom line is that once you reach the age of around 20 you don’t need to drink milk any more, so stop. Easy Pezzy, no more Lactose intolerance.
Questions? – jug