Nutrients refer to the chemicals contained in food that can sustain life and promote the growth, development and health of the body. Nutrients needed by human body are divided into six categories, namely, protein, fat, carbohydrates, vitamins, inorganic salts and (trace elements) and water. Some people separate the dietary fiber of carbohydrates, which is called the seventh largest nutrient. In protein, the amount of food such as fat and carbohydrate is relatively large, so it is called macronutrient. Vitamins and inorganic salts (minerals) need less, which are called micronutrients. Inorganic salts that account for more than 0.0 1% of the total weight of human body are called macro elements. And those whose total weight is less than 0.0 1% are called trace elements. Carbohydrate, fat and protein are oxidized and decomposed in the body to produce a certain amount of heat energy to meet the heat energy needs of the human body, which is called thermogenic nutrients.

Nutrients are divided into five categories according to their chemical properties and physiological functions, namely, protein, lipids, carbohydrates, minerals and vitamins.

1, protein: It is an important component of cells, tissues and organs, an important component of functional factors and regulatory factors, and the material basis of all life.

2. Lipids: including fats and lipids. Fat is an important energy storage and supply substance in the body, and lipids are an important component of cell membranes, tissues and organs, especially nerve tissues. Lipids are also important nutrients in the diet. When cooking, they give food special color, fragrance and taste, stimulate appetite. Proper intake can meet the physiological needs of the body and promote the absorption and utilization of fat-soluble vitamins such as vitamin A and vitamin E.

3. Carbohydrate: It is an organic compound composed of three elements: carbon, hydrogen and oxygen. It widely exists in animals and plants, including skeleton substances that constitute animal body structure and substances that provide raw materials for energy metabolism. It is the main source of human dietary energy.

4. Minerals: refers to all kinds of elements in nature except carbon, hydrogen, oxygen and nitrogen contained in human tissues. All minerals with a body content greater than 0.0 1% of body weight become macro elements or macro elements, including calcium, phosphorus, sodium, potassium, sulfur, chlorine and magnesium; Minerals whose body content is less than 0.0 1% of body weight are called trace elements.

5. Vitamins are a kind of trace organic compounds with low molecular weight that are necessary to maintain the life activities of the body. According to its solubility, it can be divided into fat-soluble vitamins and water-soluble vitamins. Fat-soluble vitamins include vitamins A, D, E and K, which often exist with lipids in food; Water-soluble vitamins, including B vitamins and vitamin C, are stored in a small amount in the body and are easily excreted from urine, except for vitamin B 12, which is easily stored in the body.