Each of the nutrients performs its specific functions in the human body and is part of almost all cellular elements and enzymatic systems.
In the process of transformation from food substances specific for a given individual substance are synthesized.
Proteins are of exceptional importance in the life of the body. Without them, life, growth and development of the body are impossible. It is a plastic material for the formation of cells and intercellular substance. Proteins are part of hormones, immune bodies, enzymes. They participate in the exchange of vitamins, minerals, and the delivery of oxygen, lipids, carbohydrates, vitamins, hormones, and drugs by the blood. Fats and carbohydrates can form from proteins, but proteins cannot be replaced by other nutrients.
The earliest manifestation of protein deficiency is a decrease in the protective properties of the body in relation to the action of adverse environmental factors. With a lack of proteins, digestion, hematopoiesis, the activity of the endocrine glands, nervous system are disrupted, the growth and development of the body are inhibited, the mass of muscles, liver is reduced, trophic disturbances of the skin, hair, and nails occur. Protein deficiency weakens mental activity and reduces human performance. It can develop not only as a result of an inadequate intake of proteins with food, but also as a result of a violation of the principles of a balanced diet, in the event of various diseases, when the digestion and absorption of proteins and amino acids is disturbed.
Excessive intake of proteins in the body causes increased functioning of the digestive apparatus, the formation of degradation products in the intestines and incomplete breakdown, which can lead to intoxication and an increase in the load on the liver, kidneys, and impaired brain function.
Fats supply the body with energy, polyunsaturated fatty acids, phospholipids (lecithins), and sterols. They participate in plastic processes, contribute to the intake of fat-soluble vitamins - retinol (vitamin A), ergocalciferol (vitamin E), a-tocopherol (vitamin E), phylloquinones (vitamin K) - and their absorption. Fats improve the palatability of food. Their insufficient intake into the body can lead to dysfunction of the central nervous system, a disease of the skin, kidneys, organ of vision, and a decrease in body resistance.
Carbohydrates are the main source of energy. They are necessary to ensure metabolism. Carbohydrates also play a plastic role, as they are part of cells and tissues, stimulate the assimilation of proteins, contribute to the normal activity of the liver, muscles, nervous system, heart and other organs. The complete exclusion of carbohydrates from food dramatically disrupts the vital activity of the body; there is a significant loss of body weight, the assimilation of proteins and fats deteriorates, and mineral salts are lost. At the same time, carbohydrates are the main source of fat formation in the body, therefore, their excessive consumption leads to obesity. For every extra 100 g of carbohydrates, 30 g of fat are formed, which accumulates in the body, and an excess of sugar leads to disruption of cholesterol metabolism and an increase in its level in the blood.
Vitamins provide the normal course of biochemical and physiological processes in the body, being biological regulators of metabolism and entry into enzymes.
The activity of all systems and organs, the protective functions of the body depend on the degree of provision with its vitamins. Since vitamins in the human body are synthesized in very small quantities, and many are not synthesized at all, they must be supplied in sufficient quantities with food.
Minerals are vital to the human body and, along with other nutritional components, are an essential part of the diet. They play a large role in plastic processes, are part of all body tissues, especially bone tissue. Minerals are involved in metabolic processes; in the synthesis and maintenance of enzyme functions; are part of vitamins, hormones; normalize water-salt metabolism; maintain an acid-base state.
The role of amino acids in proteins and nutritional
The biological value protein foods depends on the amount and ratio of them to amino acids, particularly essential (which can not be synthesized in the body and fed with food only).
There are only 8 essential amino acids (lysine, methionine, tryptophan, phenylalanine, leucine, isoleucine, threonine, valine), and for the child's body - 10 (also arginine and histidine). Each of them plays a specific biological role. Particularly deficient are lysine, methionine and tryptophan. The adult's need for lysine is 3-5 g per day; its deficiency in the body leads to impaired growth, circulation, calcification of bones, to a decrease in hemoglobin in the blood. Methionine is involved in the metabolism of fats and phosphatides, is the most potent drug (preventing liver obesity), and is involved in the metabolism of cyanocobalamin (vitamin B | 2) and folic acid. It is necessary for the normal functioning of the adrenal glands. The daily human need for methionine is 1 g. Tryptophan promotes growth, education
6 Table. Protein content in the basic foodstuffs,%
|product Name||protein||product Name||protein|
|Pork lean||14||Wheat Bread||21,0|
|Chickens||18-20||- "- oatmeal||11,0|
|fat cottage cheese||14,0|
|- "- low-fat||18,0||White cabbage||1,8|
|Rye bread||6,0||Apples, pears||0,4|
|- "- wheat||8,1||Blackcurrant||1,0|
hemoglobin, whey protein, is involved in the process of tissue repair. The body's need for it is 1 g per day. Phenylalanine is involved in the functioning of the thyroid gland and adrenal glands. Leucine, isoleucine and threonine affect growth processes. With a lack of leucine, body weight decreases, changes occur in the kidneys and thyroid gland. Lack of valine leads to impaired coordination of movements.
Histidine is part of hemoglobin, its deficiency or excess in the body worsens conditioned activity. Arginine is involved in the formation of urea, the end product of protein metabolism.
Essential amino acids perform various functions in the body and play no less physiological role than essential ones. For example, glutamic acid is the only acid that supports the respiration of brain cells.
Amino acids are found in all products of plant and animal origin, with the exception of refined products such as sugar, starch, various oils. However, the content and ratio of them in the products is different. Products of animal origin - milk, meat, fish, eggs - contain essential amino acids in the most favorable proportions. Milk protein is especially valuable because it contains deficient amino acids - tryptophan, lysine, methionine - in the best ratio. Lean meat contains more protein than fat. There are a lot of proteins in such products of plant origin as peas, beans, buckwheat and pearl barley, millet, rice. The protein content in staple foods is given in table. 6.
The rate of digestion of proteins in different foods is different. Fish and milk proteins are digested quickly, meat proteins take a little longer and proteins of cereals and bread are digested even longer. The speed and completeness of protein digestion is influenced by the culinary processing of products. Boiling food increases the absorption of proteins.
Lipids are a group of organic compounds that include fats (or triglycerides) and lipoids (fat-like substances). Lipoids, which are especially important in the human body, include sterols (in particular, cholesterol) and phospholipids.
The biological value of the fat is, first of all, their high energy consumption. However, in humans, and they perform other vital biological functions. In the form of compounds with fats, proteins are part of cellular membranes and nuclei involved in the regulation of metabolism in the cells.
Deficiency of fats in food weakens the immune system and, therefore, reduces the resistance to infections. With insufficient intake of fats, the body's need for energy is satisfied mainly due to carbohydrates and, in part, proteins, which increases the consumption of proteins and essential amino acids.
Together with fats, fat-soluble vitamins (retinol, or vitamin A; ergocalciferol, or vitamin O, tocopherols, or vitamin E, phylloquinones, or vitamin K) and biologically important phospholipids (lecithin and choline) enter the body.
Fats consist of glycerol and fatty acids, which can be saturated (palmitic, stearic, butyric, caproic, etc.) and unsaturated (oleic, linoleic, linolenic and arachidonic). Linoleic, linolenic and arachidonic acids are polyunsaturated fatty acids. Arachidonic acid is synthesized in the body from linoleic acid, which is an indispensable component of nutrition.
Polyunsaturated fatty acids increase elasticity and reduce the permeability of the vascular wall, form readily soluble compounds with cholesterol and increase its excretion, ensure the normal growth and development of the body, enhance the lipotropic (decreasing fatty liver infiltration) effect of choline and contribute to its synthesis.
The minimum daily requirement of an adult in linoleic fatty acid is 2-6 g, which is contained in 10-15 g of vegetable oil (sunflower, corn, cotton).
To create a certain excess of linoleic acid in the body, it is recommended to add 20-25 g of vegetable oil to the daily diet.
There is no absolute deficiency of linoleic acid in the diet, but there are cases of insufficient consumption. So, if a person consumes 100 g of butter per day and does not consume vegetable fats at all, then the body receives only about 1 g of linoleic acid. Deficiency of polyunsaturated fatty acids can also occur in children of the first year of life when they are fed with milk formulas made from cow's milk (human milk contains 12-15 times more linoleic acid than cow's). In this regard, vegetable oil, which is a source of linoleic acid, is introduced into modern infant formula ("Baby").
With insufficient intake of linoleic acid with food, the synthesis of arachidonic acid, which is a vital substance, is disrupted. Of animal fats, arachidonic acid contains most of all pork and especially fish oils.
The need of the human body for fats depends on the nature of work, gender, age and other factors. The harder the physical labor, the greater the need for fats. This takes into account not only explicit fats that come with those or other fatty foods, but also hidden ones contained in other foods.
Currently, the population of economically developed countries consumes fatty foods in an amount corresponding to 40–45% of the total energy value of the diet. In our country, there is also an increase in the consumption of fat products. This is a dangerous trend. Excessive enthusiasm for fatty foods adversely affects the state of the body, leads to the development of various diseases, in particular blood circulation organs, etc.
Very valuable for the human body is lecithin, which is found in many foods. This lipoid is involved in the exchange of cholesterol, helps to remove it from the body. In general, phospholipids, which include lecithin, contribute to better absorption and absorption of nutrients. Cells of the nervous system are especially rich in them. Phospholipids improve oxidative processes, stimulate growth, increase the body's resistance to oxygen starvation and the action of high temperature.
Phospholipids are found in large quantities in eggs (3,4%), unrefined vegetable oils (1-2%), cheeses (0,2-1,1%), meat (0,8%), poultry (0,5— 2,5%), fish (0,3-2,4%), butter (0,3-0,4%), bread (0,3%) and other grain products.
The role of cholesterol in the human body
A constant component of fatty foods are sterols, of which cholesterol is the most studied. It is present in all cells and tissues of the body, especially a lot of it in the nervous tissue and brain (4%), less in the liver (0,3%) and muscles (0,2-0,25%).
The blood serum of healthy people contains 3,6 mmol / l of cholesterol.
Cholesterol is necessary for the formation of adrenal hormones, sex hormones, calciferols and other important compounds. Being a constant component of the cellular contents, it is involved in maintaining a certain level of water in the cell, transporting various substances through cell membranes. He has the ability to bind some poisons, contributing to their neutralization.
Along with a positive role, cholesterol in metabolic disorders is involved in the development of atherosclerosis and coronary heart disease. High cholesterol in the blood leads to these diseases. Blood cholesterol is associated with protein substances in lipoproteins. Part of the so-called a-lipoproteins (high density lipoproteins) cholesterol does not stimulate the development of atherosclerosis. On the contrary, a high content of a-lipoproteins in human blood is considered an anti-sclerotic factor. An increase in blood levels of p-lipoproteins (low density lipoproteins) with a large amount of cholesterol contributes to the development of atherosclerosis and coronary heart disease. Low density lipoprotein cholesterol is deposited in the walls of the arteries and condenses them.
In the human body, as a result of metabolism, a constant level of cholesterol is maintained both due to its intake with food, and due to the synthesis of fats and carbohydrates. The source of food cholesterol is animal products. Especially a lot of it in egg yolks, butter, beef fat, sour cream, animal brains.
With food, 0,5 g of cholesterol enters the body daily, and much more is synthesized. Limiting cholesterol in food dramatically stimulates its synthesis. Previously, excess cholesterol in food was considered the main nutritional factor for the development of atherosclerosis, so it was recommended to sharply limit and even exclude foods containing this substance from food. Currently, scientists associate the development of atherosclerosis with excessive consumption of animal fats (rich not only in cholesterol, but also saturated fatty acids), simple carbohydrates, and metabolic disturbance as a result. Reception of cholesterol with a beggar within the daily norm (0,6 g) does not significantly increase its level in the blood. Thus, the observation showed that with the daily use of two eggs containing 0,4-0,5 g of cholesterol for 54 days, its level in the blood of healthy young people does not noticeably change. However, if these same people ate 9 yolks a day, supplying the body with about 2 g of cholesterol, then after 2 weeks its content in the blood increased significantly.
When lipid metabolism is disturbed, eating food containing even a slightly increased amount of cholesterol leads to an increase in its level in the blood. Therefore, in the diet of patients with atherosclerosis, coronary heart disease, as well as in the diet of the elderly and old people, foods high in cholesterol should be limited. However, even in these cases, eggs and milk fats should not be excluded from the diet. In egg yolks, cholesterol is combined with lecithin, which improves cholesterol metabolism and prevents the development of atherosclerosis. Sour cream and cream contain more lecithin than butter, so they need to be widely used in the diet of the elderly.
There is no cholesterol in vegetable oils. It contains phytosterols (R-sitosterol), which have biological activity. They contribute to the normalization of fat and cholesterol metabolism. Under the influence of polyunsaturated fatty acids contained in vegetable oils, cholesterol is transferred from cells to blood plasma and excreted from the body, partially converted by the liver into bile acids, which enter the intestines. In the intestines, part of the cholesterol received with bile, under the influence of microorganisms constantly present here, turns into insoluble substances and is excreted from the body.
Carbohydrates and their role in nutrition
There are two main groups of carbohydrates: simple and complex. Simple carbohydrates include glucose, fructose, galactose, sucrose, lactose, and maltose. The complex ones are starch, glycogen, fiber and pectin. The main source of carbohydrates in human nutrition is plant foods, and only lactose and glycogen are found in animal products. Simple carbohydrates are easily soluble in water, quickly absorbed in the food channel and easily absorbed. They have a pronounced sweet taste.
Sucrose is used in human nutrition as predominantly sugar.
Sweet foods and drinks (third courses) are useful at the end of a meal, as they inhibit the secretion of gastric juice and create a feeling of fullness.
Lactose - milk sugar - is found only in milk (4-6%) and dairy products. In the presence of lactose, lactic acid bacteria develop, which inhibit the growth of other microorganisms in the intestine.
Complex carbohydrates are poorly soluble in water and are absorbed into the body gradually, after cleavage by appropriate enzymes to simple carbohydrates. In human nutrition, starch is the main carbohydrate; it makes up 75–80% of consumed carbohydrates per day. Starch is found in large quantities in the grains of wheat, rye, barley, rice, corn, and up to 20% of starch contains potatoes. Therefore, the main source of starch supply to the body is bread, cereals, potatoes (table. 7).
7 Table. The total amount of carbohydrates in the food 100 g (core carbohydrate source)
Glycogen, or animal starch, is a complex carbohydrate of animal origin. It is found in small amounts in the liver and meat. In the human body, glycogen is formed from glucose. It accumulates in the liver and muscles. With significant physical exertion, glycogen can be used as a backup energy material.
Under ordinary conditions of glycogen maintains normal liver function.