Food systems
About healthy nutrition
With a rational diet, food should, firstly, contain the necessary amount of protein, fat, carbohydrates, salts and vitamins for a person, secondly, create a sense of satiety and, thirdly, be pleasant to the taste, moderately stimulating the activity of the digestive tract.
During the digestion of food in the gastrointestinal tract (GI), proteins, fats and carbohydrates are decomposed into more or less simple substances, which are then absorbed by the intestinal walls, enter the bloodstream and spread throughout the body.
In the body, substances are burned (oxidized), releasing carbon dioxide (CO2) and water (H2O). The heat generated from their combustion is partly used to maintain body temperature, and partly converted into other types of energy consumed by muscles and organs.
The amount of heat energy is usually measured in calories. By the way, a calorie is the amount of heat that can increase the temperature of 1 liter of water by 1 degree.
So, energy consumption, and hence the need for food, depend not only on the gender and age of a person, but also on their lifestyle, that is, on the work they do. For example, people who are engaged in mental work should get about 3,000 calories a day, and people who are engaged in physical work have a higher energy expenditure the more they perform muscle movements. With mechanized work, this expenditure is 3,500 calories, and with very hard work, it can even exceed 5,000 calories!
