In terms of their value, the proteins that make up food are not the same. Some of them are close in their construction and chemical composition to the proteins of the human body, that is, they contain all the constituent parts (amino acids) necessary for the construction of these proteins; others are significantly different from them and therefore less valuable. Proteins with high nutritional value include proteins of meat, fish, milk, eggs, and proteins of certain vegetables. So, high-grade proteins are contained in potatoes, cabbage. The value of croup proteins is not the same. In terms of amino acid composition, proteins of oatmeal, rice, and buckwheat should be considered more valuable. In contrast, millet, semolina, pearl barley contain proteins that are characterized by relatively lower nutritional value. These grains can be enriched with missing ingredients (amino acids) at the expense of other foods rich in such substances. Thus, the nutritional value of wheat can be increased due to the amino acids contained in meat, milk, and also in various vegetables.
Fats, like carbohydrates, are the main sources of energy and determine mainly the caloric content of food. In addition, fats perform protective functions in relation to protein, since with a sufficient content of them in the body less protein is destroyed than with a lack of these substances. In animals and humans, fats can be deposited not only with an excess of them in the diet, but also when a sufficient or excessive amount of carbohydrates is included in the food. Consequently, fats in the body are built not only from the fat itself, but also from carbohydrates and protein.
Animal fats are considered more complete than vegetable fats, since most animal fats carry specific vitamins.
Milk fats are most useful for humans, such as butter and ghee, cream fats, sour cream. But other fats, including margarine and vegetable oil, are valuable food products because they have a high calorie content and good digestibility.
Carbohydrates are especially rich in products of plant origin: cereals, vegetables, fruits. From animal products, some carbohydrates are found in milk (in the form of milk sugar).
Carbohydrates can be found in foods in the form of starch or in the form of various sugars, such as fructose; Both those and other carbohydrates are well absorbed in the human body; the difference between them is that pure sugar dissolves quickly in water and is instantly absorbed into the blood (so-called fast carbohydrates), while starch and fructose under the action of digestive juices undergo a gradual breakdown and enter the blood not immediately, but over a long period period (so-called. Slow carbohydrates).
Under special conditions, such as, for example, in cases of heart failure, with severe mental or physical fatigue, carbohydrates are required to be rapidly introduced into the body; in this case, sugar is needed, which is sometimes injected as glucose even directly into the blood (through a vein). In the normal state of the body, the main amount of carbohydrates is eaten in the form of starch and only a small part (60-100 g per day) in the form of sugar.
Vitamins are divided into groups according to their solubility: vitamin C and vitamins of group B are water soluble, vitamins A, D and E are soluble in fats and are called lipovitamins.
Vitamins are often called an additional factor of nutrition. This name does not correspond to the real value of vitamins: they are elements of food, as necessary as all other substances that make up the human body. It is known that in the absence of one or another vitamin in food, very serious violations of the activity of various organs and of the whole organism are observed. Such violations - avitaminosis, for individual vitamins are expressed in certain typical phenomena.
It is much more difficult to recognize and identify hypovitaminosis, that is, such violations, which are observed not in the complete absence, but with a lack of a vitamin in food.
When studying the physiological significance of vitamins, it becomes clear that their action is much more extensive than the prevention of a particular beriberi. All vitamins in their effects on the human body are dependent on one another. Therefore, the lack of one of them can disrupt the use of others.