Milk contains less sugar, which is an important source of energy for the human body. If you only drink milk for breakfast and do not eat staple food, you can not get enough sugar as energy, forcing the body can only be taken from the milk protein to replace sugar as energy supply, and protein is originally used to replenish the human body tissues within the protein consumption, which results in a waste of protein. Therefore, it is best to drink milk with a staple food, such as bread, cake, cookies, etc., or add some cereal in the milk.