The growth and development of organisms depend on the process of substance metabolism in the body. The new substances obtained in the process of substance metabolism in the body are mainly absorbed from food. The comprehensive process of obtaining and utilizing food is called nutrition. Nutrition is an important factor to ensure the normal growth and development of human body. Reasonable nutrition can promote health and can be used as a means to prevent and treat diseases.
Nutrition and physical exercise are both important factors to maintain and promote human health. Nutrition is the material basis of body tissue, and physical exercise can enhance the function of the body. The scientific cooperation of the two can effectively promote physical development and health. Only paying attention to nutrition without necessary nutrition guarantee, the material and energy consumption in the body can not be compensated, which will have an adverse impact on physical health or physical development. Reasonable nutrition requires that the diet must contain all the nutrients needed by the body. Appropriate contents of various nutrients can fully meet the needs of the body, maintain the normal physiological functions of the body and promote growth and development. This diet is called a "balanced diet". In addition, reasonable nutrients also require that food is easy to digest and absorb, and does not contain harmful substances. In order to choose food correctly and give full play to the nutritional function of food, we must understand the nutritional knowledge.
Second, nutrients
Nutrients are substances that can be digested and absorbed in the body, can provide heat, constitute body tissues and regulate physiological functions, and are necessary for normal substance metabolism in the body. The nutrients the human body needs are sugar, fat, protein, vitamins, minerals and water. Various nutrients have their own unique functions, but they are closely related in the process of metabolism in the body. Their basic functions and proportions in the human body are as follows:
Basic functions of nutrients and their proportion in human body
Carbohydrate 1% ~ 2%
10% ~ 15% fat heating energy.
Protein 15% ~ 18%
55% ~ 67% water
4% ~ 5% of inorganic salt
Vitamins for regulating physiological functions (trace)
dietary fibre
(1) protein
Protein is composed of carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus and other elements, mainly containing nitrogen. The basic unit of protein is amino acid. Protein is the main component of cells, accounting for 80% of the solid components in cells. Muscle, blood, mucous membrane, tendon, cartilage, skin and other tissues are mainly composed of protein. Protein is also the main substance for tissue regeneration and repair after growth and injury.
When protein is lacking for a long time, protein deficiency will appear in the body: intestinal mucosa will be affected first, and symptoms such as indigestion and chronic diarrhea will appear; Liver function declines, plasma protein synthesis is hindered, plasma protein concentration decreases, and edema may occur; The enzyme activity decreased; Globulin decreases and resistance decreases; When the body's stress ability decreases, the child's growth and development will be slow, and even mental retardation will occur; Adult weight loss, muscle atrophy, anemia; Women also have menstrual disorders.
Protein's storage in the body is very small, and it can be stored in a small amount under the condition of adequate nutrition. Excess protein enters the body and is decomposed into urea by the liver. Therefore, we should supplement the right amount of protein every day to meet the needs of the body.
(2) Fat
Fat is composed of carbon, hydrogen and oxygen, and is an important component of cells. Fat can be divided into neutral fat and lipid-like fat. Adipose tissue can store heat energy, regulate body temperature, support and protect organs. Fat is a substance with high heat energy, and 1 g fat can generate 37.65 kilocalories when it is oxidized and burned in the body. The digestion and absorption of fat is related to its melting point, and it is easier to digest and absorb when the melting point is lower than body temperature. 50 grams of fat in the daily diet can basically meet the needs of the human body. It is generally believed that fat should account for 17% ~ 20% of the total daily calorie supply, and should not exceed 30%. Too much fat is harmful to human body, which will cause obesity and metabolic disorder, and is the main cause of hypertension, hyperlipidemia, coronary heart disease and gallstones. Fat comes from animal foods, such as lard, butter, cream, fish oil and egg yolk, and also from plant foods, such as sesame, rapeseed, soybean and peanut.
(3) Sugar (carbohydrate)
Sugar, also known as carbohydrate, is the most important economic and thermal substance. The heat energy provided by sugar is easier to digest and absorb than fat and protein. Fast decomposition, fast heat production and low oxygen consumption. It can also decompose and release heat energy under aerobic or anaerobic conditions. Sugar is an important substance that constitutes the body. Sugar can increase the storage of liver glycogen and maintain and enhance liver function. Glucuronic acid is directly involved in the detoxification function of the liver. Sugar is an important substance to maintain the normal physiological function of the central nervous system and the only energy source for the brain. Brain tissue has no energy reserve, and energy is supplied by blood sugar. When the blood sugar drops below the normal value, the brain tissue may have hypoglycemia symptoms such as dizziness and fainting due to insufficient energy supply materials. When the body is short of sugar, the working ability of the heart and skeletal muscle decreases. Insufficient glycogen storage in skeletal muscle leads to insufficient endurance. Lack of myocardial glucose can lead to angina pectoris.
The supply and consumption of sugar should depend on the nature of work and labor intensity. The greater the labor intensity and the longer the time, the more sugar is needed. Generally speaking, sugar accounts for 60% ~ 70% of the total daily calorie supply. Usually adults need about 4 ~ 6 grams per kilogram of body weight every day, while athletes need 8 ~ 12 grams. The sugar reserve in the human body is very small, about 300 grams. Therefore, it must be taken from the diet every day. Studies have shown that excessive intake of sucrose is harmful to health, which is related to obesity, diabetes, cardiovascular diseases, dental caries, myopia and other diseases.