The so-called acidity and alkalinity of food means whether the inorganic salts in food are acidic or alkaline. General metal elements such as sodium, calcium, magnesium, etc. are alkaline in human body, and foods containing more of these elements are alkaline foods, such as soybean, tofu, spinach, lettuce, radish, potato, lotus root, onion, kelp, watermelon, banana, pear, apple and milk. Some foods contain more nonmetallic elements, such as phosphorus, sulfur, chlorine, etc. After oxidation in the human body, acid radicals with anions are generated, which belongs to acidic foods. Such as pork, beef, chicken, duck, eggs, carp, oysters and shrimps, as well as flour, rice, peanuts, barley and beer.