Why do I get diarrhea when I drink yogurt?

It is the inability to absorb the lactose in milk. Drinking milk or milk powder will cause abdominal distension and diarrhea, which is called lactose intolerance.

Lactose is a disaccharide that is widely found in mammalian milk. There are approximately 4.5 grams of lactose per 100 ml of milk. Lactose is broken down into glucose and galactose by lactase in the human small intestine before it can be absorbed. In fact, we can decompose lactose when we are just born, but the content of the enzyme that decomposes lactose gradually begins to decrease, so that when we grow up, we cannot decompose lactose, resulting in lactose not being absorbed. Lactose intolerance simply means that lactose cannot be decomposed and absorbed in the small intestine, causing lactose to enter the large intestine, resulting in high osmotic pressure in the intestine, inability to absorb water, and diarrhea. The principle is somewhat similar to laxatives.

For people who experience diarrhea, bloating or stomach discomfort after drinking milk, it is usually due to a lack of a digestive enzyme called lactase. The milk you drink contains a large amount of lactose, and they do not have the enzyme lactase. The lactose cannot be broken down and absorbed, and a large amount of undigested lactose reaches the large intestine. Some bacteria in the large intestine use lactose to ferment, producing a large amount of gas, which can cause symptoms such as bloating, diarrhea, and farting. Lactose intolerance can cause abdominal bloating in mild cases, and necessitate the toilet soon after drinking milk in severe cases.