Some people find that when they catch a cold, their stomach hurts from the milk. If it was a common milk intolerance, they would not digest milk in principle, but here only during illness.
Usually it's the milk sugar lactose. Everyone is accustomed to the fact that if the enzyme lactase is not produced in the intestine, then milk begins bloating, pain and diarrhea. With age, this happens to many.
All the trick is in the villi of our intestines. In order for the intestines to absorb food, its surface is not just bumpy, but all covered with microscopic villi. This is designed by nature to increase the suction area.
So the enzymes that break down milk sugar are localized at the very tips of the intestinal villi. If there is some kind of infection or inflammation in the intestines, then the tips of the villi are the first to die. Together with lactose digesting enzymes.
The villi regenerate after a few days with full armor and enzymes attached to their place. Therefore, lactase deficiency disappears.
Bacteria
There are still oddities with the intestinal flora. Sometimes in the small intestine germs begin to grow. Although there are usually very few of them. At the same time, a person has his own native lactase, which is ready to digest milk sugar, but microbes intercept it on arrival, and even healthy villi cannot digest anything. Microbes begin to make hydrogen from this lactose, and bloating begins. It's not fair. Because there were enzymes.
On the other hand, sometimes people do not have the enzymes to digest lactose, and the microbes in the large intestine fatten on it. But it turns out that on a hearty milk diet, the composition of microbes changes so that they assimilate not only lactose, but also the hydrogen obtained as a result of its fermentation. It turns out that bloating is reduced, and a person without enzymes suffers less. We discussed this in the topic about gas in the intestines.
It just seems to me that even those who do not have colds attack the intestines cannot stand milk. Although... who knows them there, these viruses.
