I. Energy
A unified unit, namely Joule (J) or cal, has been established internationally.
lk cal = 4. 184 kjlkj = 0.239 kcal l 000 kcal = 4.l 84 MJ(MJ)。
1MJ (megajoule) = 239 kcal energy coefficient: refers to the energy value produced by nutrient oxidation per gram of productivity in the body.
Each gram of fat can release 9 kilocalories, each gram of protein and carbohydrate can produce 4 kilocalories, each gram of alcohol can produce 7 kilocalories (but alcohol is not a nutrient, which is not conducive to the growth, maintenance and repair of body tissues), and each gram of dietary fiber can produce 2 kilocalories.
Second, carbohydrates
Carbohydrate is the main energy source for special problems.
After glucose produced by carbohydrate digestion is absorbed, a part of it is stored in liver and muscle in the form of glycogen.
Hepatic glycogen is mainly used to maintain the relative stability of blood sugar level.
Reference Intake of Carbohydrate and Food Sources: Suggestions from China Nutrition Society;
The reference intake of dietary carbohydrates for China residents is 50-65% of the total energy intake.
Requirements for carbohydrate intake: including carbohydrate starch, indigestible resistant starch, non-starch polysaccharides and oligosaccharides; Limit the intake of pure energy food, such as sugar, to ensure the needs of human energy and nutrients, improve the gastrointestinal environment and prevent dental caries.
The main sources of starch in the diet are cereals and potatoes. Cereals generally contain 60%-80% carbohydrates, 15%-29% potatoes and 40%-60% beans. GI: referred to as glycemic index for short, refers to the ratio of the blood glucose tolerance curve area of different foods at baseline to the postprandial standard sugar (glucose) tolerance area, expressed as a percentage.
GI is an index used to measure the influence of a certain food or a certain dietary component on blood sugar concentration.
Foods with high GI may indicate that after entering the gastrointestinal tract, they are digested quickly and absorbed completely, and glucose enters the blood rapidly, and the blood sugar concentration fluctuates greatly. On the contrary, the fluctuation of blood glucose concentration is small.
Third, lipids.
Fat is also an important energy substance. Under normal circumstances, 40%-50% of the energy consumed by the human body comes from the body fat. In the case of short-term hunger,
Energy is mainly supplied by body fat. But it can't supply energy when the human body lacks oxygen.
Classification: Neutral fat: It is composed of one molecule of glycerol and three molecules of fatty acid, so it is called triacylglycerol or triglyceride.
It accounts for about 95% of lipids. Most of the fat is distributed in subcutaneous tissue, omentum, mesentery and its surrounding tissues.
Fatty acid: It is the basic unit of triglyceride.
1. According to the carbon chain length of fatty acids, it can be divided into: long-chain fatty acids (containing more than carbon 14); Medium chain fatty acids (containing 8- 12 carbons); Short chain fatty acids (containing 2-6 carbons).
2. According to the degree of fatty acid saturation, it can be divided into: saturated fatty acid (animal fat); Monounsaturated fatty acids; Polyunsaturated fatty acids. The ratio of the three types is1:1:1; The overall function accounts for 20% ~ 30%; Essential fatty acids are derived from linoleic acid and linoleic acid in polyunsaturated fatty acids. Two linolenic acids;
3. According to the spatial structure of fatty acids, it can be divided into: cis fatty acids; Trans fatty acids (which increase the risk of cardiovascular disease). The intake of trans fatty acids should not exceed 2.2 grams per day, and should be lower than 1% of total daily energy. Lipids (immobile lipids): mainly phospholipids (lecithin, sphingomyelin), glycolipids (constituting cell membranes), steroids (cholesterol and phytosterols), etc.
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