Because when drinking milk on an empty stomach, protein, which is extremely useful to human body, will be regarded as carbohydrate and converted into heat, which is just like using oil instead of coal as fuel, which is uneconomical.
To give full play to the nourishing effect of milk on the body, it is best to eat some slow food, biscuits, porridge and other foods first, and then mix them with milk to give full play to its due nourishing effect, so as to achieve the effect of nourishing the body.
Besides, it is better to drink milk slowly than quickly. Dragging milk will reduce the chance of milk mixing saliva in the mouth, and the fat will form lumps and form indigestible substances, which will cause diarrhea for people with weak intestinal function or abdominal distension and discomfort due to abnormal fermentation.