The main functions of protein are: 1, which constitutes the tissues and organs of the human body; 2. Important substances in the human body, such as enzymes, hormones and antibodies; 3. Supply heat energy. The daily requirement of adults is1.0 ~1.2 g/kg. Protein widely exists in animal and plant foods. The quality of animal protein is good, but it is rich in saturated fatty acids and cholesterol, while the utilization rate of plant protein is low.

Lipids include:

1, the role of triglyceride (fat) includes (1) as the storage form of energy in the body; (2) maintaining normal body temperature (3) protecting internal organs; (4) Help the body to use carbohydrates more effectively and save protein; (5) forming cell membrane; (6) synthesizing important substances of human body; (7) participating in cholesterol metabolism; (8) Provide fat-soluble vitamins such as A, D, K, E, etc., and also promote their absorption in the intestine. The main sources are: (1) animal fat contains more saturated fatty acids and monounsaturated fatty acids, but less polyunsaturated fatty acids; (2) Vegetable oil: mainly contains unsaturated fatty acids.

2. The functions of phospholipids include: (1) providing heat energy; (2) constitute the cell membrane; (3) Help lipids or fat-soluble substances to pass through the cell membrane smoothly; (4) As an emulsifier, it is beneficial to the absorption, transport and metabolism of fat. Mainly from egg yolk, animal liver, soybean, wheat germ, peanuts and so on.

3. The functions of sterols include: (1) forming cell membrane; (2) Synthesis of important active substances in human body. Mainly from animal brain, liver, kidney, eggs, meat, milk and so on.

The main functions of carbohydrates are: 1, storage and energy supply; 2, it is a component of the body; 3. Save protein; 4. Anti-ketogenic effect; 5, provide dietary fiber, increase the volume of feces and promote gastrointestinal peristalsis. The heat provided accounts for 60% ~ 65% of the total heat energy. Different kinds of carbohydrates come from different sources: fructose comes from fruits, honey and so on; Sucrose comes from sugarcane, sweets, honey, etc. Lactose comes from milk and dairy products; Trehalose comes from edible mushrooms, etc. Starch comes from potatoes, beans and cereals; Cellulose is contained in all plants (such as wheat products); Hemicellulose comes from wheat, rye, rice, vegetables and so on.