Nutrients refer to substances that the human body must ingest from the outside in the form of food in order to maintain survival and health and ensure growth and physical labor. Nutrients include protein, fat, carbohydrates, inorganic salts, vitamins and water. Its main functions are as follows:

(1) It supplies the body with heat energy needed for physiological activities and labor, such as protein, carbohydrate and fat.

(2) constituent of body tissues, such as protein.

(3) regulating physiological functions, such as various vitamins, inorganic salts and protein.