The three nutrients refer to protein, carbohydrates and fat. 1. Protein: is the material basis of all life, is an important part of the living cells; at the same time, protein can also be used as a carrier for normal human activities, transporting a variety of substances in the body, such as hemoglobin; Proteins are also involved in human antibodies and immunity, in which many white blood cells, lymphocytes, etc. are composed of proteins; proteins are also involved in enzyme catalysis, as well as hormone regulation, energy supply, etc. in the body. 2. Carbohydrates: Carbohydrates are part of the cellular structure of life, and the main energy-supplying substances, and also regulate cellular activity. 3. Fats: Fats vary greatly in chemical structure and composition, but they are also important components of living organisms. For example, the cell membrane of the organism is an important component of fat; also involved in various chemical reactions in the body, there are a number of fat-soluble vitamins, such as vitamin A, D, K, and steroid hormones, but also played a role in regulating life activities. The human body’s three major nutrients are indispensable, all play a very important biological role, so the usual diet should pay attention to the nutritional structure of a balanced, not picky, partiality.