In nutrition, foods are generally divided into two categories: acidic foods and alkaline foods. The acidity and alkalinity of food has nothing to do with the ph value of the food itself (sour food is not necessarily acidic food), which is mainly defined by the fact that food is digested, absorbed and metabolized in the human body and eventually becomes acidic or alkaline. Those that produce acidic substances are called acidic foods, such as animal viscera, muscles and plant seeds (grains). Alkaline substances are called alkaline foods, such as vegetables, melons and beans, tea and dairy products. Animal viscera, muscle, fat, protein and grain are rich in sulfur (S), phosphorus (P) and chlorine (cl), which are metabolized in human body to produce sulfuric acid, hydrochloric acid, phosphoric acid and lactic acid, which are the sources of acidic substances in human body. However, most vegetables, fruits, kelp, beans and dairy products contain many elements such as calcium (ca), potassium (K), sodium (na) and magnesium (mg), which can become alkaline substances after metabolism in the body.