Generally speaking, drinking milk on an empty stomach will not cause diarrhea. If a patient has diarrhea from drinking milk on an empty stomach, it may have a lot to do with the patient’s own health and the quality of the milk itself. Milk is rich in nutrients, and one of the components is a disaccharide called lactose. This kind of disaccharide has a large molecular weight and requires the participation of lactase to be broken down and metabolized in the body. If the human body fails to produce enough lactase in the small intestine, or if lactase fails to function in time, causing the component to reach the large intestine, it will ferment in the large intestine and produce a lot of gas, which will also stimulate the intestinal wall and speed up intestinal peristalsis, resulting in flatulence, abdominal pain, diarrhea and intestinal tinnitus. This condition is called galactose intolerance syndrome. In addition, if you drink cold milk in the morning on an empty stomach, it can also cause smooth muscle hyperfunction due to the cold effect, causing diarrhea and other conditions in the body. Of course, it is also important to make sure that the milk you drink has not expired and deteriorated. If your body is healthy and you drink hot milk that has not deteriorated, generally speaking, you will not have diarrhea. If you often have diarrhea after taking it, the main consideration is lactose intolerance, in which case you need to change to other animal sources of milk.