sugar

Sugar, also known as carbohydrate, includes sucrose (brown sugar, white sugar and granulated sugar), glucose, fructose, galactose, lactose, maltose, starch, dextrin and glycogen. Among these sugars, except glucose, fructose and galactose, which can be directly absorbed by the human body for a long time, the rest of the sugars must be converted into glucose in the body to be absorbed and utilized.

The main function of sugar is to provide heat energy. Each gram of glucose is oxidized in the human body to generate 4 kilocalories of energy, and about 70% of the energy needed by the human body is provided by sugar. In addition, sugar is an important substance that constitutes tissues and protects liver function.

100g in common foods, meat contains protein 10-20g, fish contains 15-20g, whole egg contains 13- 15g, beans contain 20-30g and cereals contain 8-1.

Protein source

The human body supplements protein by ingesting plant and animal food. Protein is mainly provided by grain, generally containing 4%. Ll% of protein, rice contains 8%-9%, and flour contains about10%-1%. Among plants, the food containing the most protein is soybean, 100g soybean contains 35g of protein, and bean products contain protein. Among animal foods, the protein content of lean meat food is about 15%-20%, the protein content of fish, shrimp and mollusk food is about 15%-20%, the protein content of milk is 2.3%, and the egg is 12.8%. The content of protein in vegetables and fruits is generally low, about below 3%.

Physiological Function of protein

1. Construct the human body: protein is the material basis of all life, an important part of body cells, and the main raw material for the renewal and repair of human tissues. Every tissue of the human body: hair, skin, muscles, bones, internal organs, brain, blood, nerves, endocrine and so on. Are made up of protein, so diet makes people themselves. Protein is very important to human growth and development.

For example, the characteristic of brain development is to complete cell proliferation at one time, and the growth of human brain cells has two peaks. The first is when the fetus is three months old; The second is the period from birth to one year old, especially 0-6 months, when brain cells grow violently. By the age of one, the proliferation of brain cells is basically completed, and its number has reached 9/ 10 of that of adults. Therefore, 0- 1 year-old children have unique intake requirements for protein, which is particularly important for children's intellectual development.

2. Repair human tissues: The human body is composed of 10 trillion cells, which can be said to be the smallest unit of life. They are in an endless process of aging, death and rebirth. For example, the epidermis of young people is updated once every 28 days, while the gastric mucosa is completely updated in two or three days. Therefore, if a person has a good intake, absorption and utilization of protein, his skin will be shiny and elastic. On the contrary, people are often in a sub-health state. Tissue damage, including trauma, can not be repaired in time and with high quality, which will accelerate the decline of the body.

3. Maintain normal metabolism and transport of various substances in the body. Carrier protein is very important for maintaining normal life activities of human body. Can carry all kinds of substances in the body. For example, hemoglobin transports oxygen (the renewal rate of red blood cells is 2.5 million/sec), lipoprotein transports fat, receptors and transporters on cell membranes.

fat

The main sources of human dietary fat are animal fat and plant fat.

Animal fat is rich in saturated fatty acids (40%~60%), but the unsaturated fatty acids content is about 30% ~ 50%. Plant fat is rich in unsaturated fatty acids (80%~90%), mainly polyunsaturated fatty acids, and the content of saturated fatty acids is only 10%~20%.

Deep-sea fish is a good source of EPA and DHA.

Foods containing more phospholipids include egg yolk, liver, soybean, peanut and wheat germ. Foods rich in cholesterol include animal offal and eggs.

There are four main effects of fat on human body:

The function of providing heat for human body. Fat is oxidized in the human body and becomes carbon dioxide and water, giving off heat. Fat produces about 2.2 times as much calories as the equivalent protein or carbohydrate. This shows that fat is an important source of heat in the body.

Functional and bioactive substances that constitute body tissues. Fat is one of the important components of human cells, especially brain nerve, liver, kidney and other important organs contain a lot of fat. Fat also constitutes body tissues and bioactive substances in the body, such as the main components of cell membranes, forming phospholipids, glycolipids and so on.

The function of regulating physiological functions. Because fat is not a good heat conductor, subcutaneous adipose tissue is an isolation layer to protect the body and prevent body temperature from escaping. So fat has the function of keeping body temperature. Fat can also store "fuel" for the body as a backup. After eating fat, the inexhaustible part can exist in the body and be reused when the body needs calories. In addition, fat can also protect internal organs, moisturize skin and prevent earthquakes.

The function of dissolving nutrients. Some vitamins that are insoluble in water but only soluble in lipids can be absorbed and utilized by the human body only in the presence of fat.

Tip:

Long-term lack of fat can easily lead to vitamin A and D deficiency, leading to dry skin, dull hair, shedding, night blindness, dry eye and other diseases.

There are three main sources of glucose in cells or plasma, namely, ① digestion and absorption of carbohydrates in food; ② When the blood glucose concentration is lower than 80- 1.20 mg/dl, it is produced by the decomposition of liver glycogen; ③ It is transformed from other non-sugar substances (such as glycerol, amino acids, lactic acid, etc.). ) in metabolism; There are also three ways of glucose in cells or plasma, namely, ① intracellular oxidative decomposition provides energy; ② glycogen was synthesized in liver or skeletal muscle when the blood glucose concentration was higher than 100mg/dL; ③ Glycogen is transformed into other non-sugar substances in cells.

(2) Lipid metabolism

The textbook focuses on three components of lipid substances familiar to middle school students, namely fat, phospholipid and cholesterol, briefly introduces the metabolic pathways and characteristics of fat, and summarizes them in the form of tabular solutions. Finally, the textbook mentioned the knowledge about blood lipid and cholesterol.

(3) protein metabolism.

The textbook also briefly introduces protein metabolism from two aspects: the source of amino acids in cells or plasma and the utilization of amino acids in cells, that is, the direction of development. Finally, the textbook summarizes this knowledge in the form of tabular solution.

The main contents are as follows: there are three sources of amino acids, namely, the digestion and absorption of protein in food, the decomposition of protein, and the transamination to produce new amino acids; There are three ways of amino acids, namely, ① synthesis of various tissue proteins and enzymes; ② New protein is produced by transamination; ③ Decomposition by deamination, in which the nitrogen-containing part is converted into urea and the non-nitrogen part is converted into other substances such as sugar and fat.