How much energy does the human body need in a day? How much is enough to eat a day?

The amount of heat needed by human daily work.

The human body consumes heat energy all the time, whether it is resting or working, it is no exception. This heat consumption can only be supplemented by three meals a day. Generally speaking, the heat energy consumed by healthy adults from food is always balanced. In order to maintain this balance, the human body must reserve a certain amount of nutrients (mainly sugar and fat) for use when hungry. When the heat energy intake exceeds the consumption, the body has a certain storage capacity and gains weight; On the other hand, if the heat energy supplied in the diet is insufficient, it is necessary to use the nutrients or tissues stored in the body to lose weight, which will affect health in the long run. Therefore, when preparing meals, we must meet the heat demand of people who eat in different situations.

A, the unit of heat energy

The unit of calculation of heat energy is usually expressed in calories. One calorie is the heat energy required to raise 1 gram of water to 1 degree Celsius at one atmospheric pressure. Because this unit is small, it is generally calculated according to 1000 times of the heat in the nutrition measurement unit, that is, the heat energy required to raise 1000 grams of water to 1 degree Celsius. In order to make a difference, the former is called "small card" and the latter is called "big card" or "thousand card". However, in nutrition, "small card" is generally not used, and it is generally called "big card".

Second, the human thermal energy demand

The heat energy needed by the human body is mainly consumed in two aspects, one is to maintain the basic metabolism of the human body, and the other is to meet the consumption of work and labor. The heat energy required for basal metabolism refers to the heat energy required to maintain constant body temperature, blood circulation, lung breathing, heart beating, gastrointestinal peristalsis, kidney excretion and other necessary activities in the body when resting in a static posture and stopping all physical and mental activities. The heat energy consumed by basal metabolism is closely related to human surface area, age, gender and climate conditions. The body surface area is large, the heat dissipation area is also large, and more heat energy is consumed. Generally speaking, the basal metabolism of young men is higher than that of women and the elderly; It is higher in cold environment than in warm environment. The basal metabolic heat energy can be calculated according to the body length and weight, and then the body surface area can be calculated. In practical work, the weight can be roughly calculated. In general, the heat consumed by basal metabolism per kilogram of body weight per hour is about L calories, so the heat energy required by basal metabolism can be calculated by the following formula: heat energy required by basal metabolism (calories) = 1 (calories) x body weight (kilograms) X 24 (hours). If a person's average weight is 60 ~ 65 kg, the daily heat energy required for basal metabolism is about 1400 ~ 1600 calories. Heat energy needed for work and labor. It varies with work, nature of labor and length of time. Strong physical labor. The longer the time, the more heat energy is consumed. In addition to the heat energy consumed by basic metabolism, the heat energy that needs to be supplemented for various degrees of labor per hour is as follows: heat energy (calories) supplements the types of labor per hour, and light labor: office work, lesson preparation, class, self-study, housekeeping, walking, meeting, theater, dressing, washing, etc., or jobs with light physical strength of 50-75. Medium labor: medium-intensity manual labor such as standing guard, typing, lecturing, cleaning guns, repairing guns, shooting vertically and singing. 75 ~ 150 Heavy physical labor: walking or marching (90 ~10 steps per minute), shooting in prone position, carpentry, porters, running, swimming and other sports 150 ~ 300 muscles. High-intensity labor: March in haste, dig fortifications, play football, basketball, ambush, fight, bump, throw grenades, cross obstacles, fight and other special intensity of more than 300 muscle movements. The total heat energy consumed by human body every day is the sum of the heat energy consumed by basic metabolism and the heat energy consumed by work. As far as everyone is concerned, the consumption of calories varies greatly due to the differences in age and weight. So there will be no difference in basal metabolism. The amount of heat energy a person needs mainly depends on the intensity and duration of labor. The total heat energy consumed by different people can be estimated according to their living and working conditions, which can be divided into three levels: light manual workers: they mainly study, have meetings or work in one day, and consume about 2400 ~ 2800 calories in one day. Moderate-intensity labor: within one day, it mainly focuses on general training, and consumes about 2800 ~ 3200 calories every day. Heavy physical labor: camping, marching, construction, automobile driving or agricultural production are the main tasks in a day, and the total calorie consumption is about 3200 ~ 4200 calories per day.

Thirdly, the calorific value of food and the reasonable distribution of heat sources.

The calorific value of food is determined by the amount of nutrients it contains. Carbohydrate, fat and protein are the main productive substances in food, and the actual heat energy they can provide in human body is: carbohydrate produces about 4 calories per gram; Fat produces about 9 calories per gram of thermal energy; Every gram of protein produces about 4 calories. Therefore, the caloric value of food is actually the sum of the heat energy generated by these three nutrients, that is, the caloric value of food is 4 calories x carbohydrate (g) 19 calories x fat (g) 14 calories x protein (g). Carbohydrate, fat and protein can supply heat energy in the body, which can replace each other to a certain extent, but at the same time they have their own special nutritional functions and cannot completely replace each other. Therefore, there must be a reasonable proportion in the diet to maximize nutritional efficiency. Of course, this ratio is also related to factors such as national agricultural production, living habits and working conditions. Generally speaking, carbohydrates are oxidized rapidly and completely in the body, which is the primary source of heat energy; Although fat produces high fever, its thorough oxidation should be carried out on the basis of carbohydrate oxidation. Only when the supply of carbohydrates is insufficient will the utilization of fat increase. In general, its heating only takes the second place. Although the egg autoplasm is mainly used as the raw material for tissue regeneration and supplements the aging part of the tissue, the protein of the aging tissue still decomposes and releases heat in the body. Under normal circumstances, the daily intake of protein is basically the same as that of protein released by aging in the body. So from the point of view of heat source, protein's intake is also a part of heat source. The reasonable distribution of heat energy in diet is as follows: the heat energy provided by carbohydrates should account for two-thirds of the total heat energy, that is, about 65%, at least not less than 50% of the total heat energy; The heat energy provided by fat should account for about 20% of the total heat energy, and not more than 30% at most. The heat energy provided by protein should account for 10 ~ 15% of the total heat energy.