Healthy eating: what does every person need to know?

Nutrition is the science of food and its impact on human health. Nutrients are chemical compounds found in food that the body uses for growth, maintenance, and energy. Nutrients that are not synthesized by the body are the most valuable (essential) and must therefore be obtained from food. These include vitamins, minerals, some amino acids, and fatty acids. Nutrients that are synthesized by the body from other compounds, even though they can be obtained from food, are not essential. Macronutrients are needed by the body in relatively large quantities, while micronutrients are needed in small quantities.

Deficiencies of certain nutrients can lead to various diseases (e.g. kwashiorkor, pellagra) and other disorders. Excessive consumption of macronutrients leads to obesity, and excess consumption of micronutrients can cause toxic manifestations.

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Macronutrients

Food consists primarily of macronutrients, which serve as a source of energy and many essential nutrients. Carbohydrates, proteins (including essential amino acids), fats (including essential fatty acids), macronutrients, and water are macronutrients. As energy sources, carbohydrates, fats, and proteins are interchangeable; fats yield 9 kcal/g (37.8 kJ/g); proteins and carbohydrates yield 4 kcal/g (16.8 kJ/g).

Carbohydrates

Carbohydrates in food are broken down to form glucose and other monosaccharides. Carbohydrates increase blood glucose levels and replenish energy reserves. Simple carbohydrates, mainly monosaccharides or disaccharides, are small molecules and are low-molecular compounds that are quickly absorbed. Complex carbohydrates are high-molecular compounds whose molecules break down to form monosaccharides. Complex carbohydrates increase blood glucose levels slowly but over a longer period of time. Glucose and sucrose are simple carbohydrates; starch and fiber (cellulose) are complex carbohydrates (polysaccharides).

The glycemic index measures how quickly carbohydrates raise blood glucose levels. The values range from 1 (slowest rise) to 100 (fastest rise, equivalent to pure glucose). However, in reality, the rate at which blood glucose rises also depends on the nature of the carbohydrates in the food.

High glycemic index carbohydrates quickly raise blood glucose levels to high levels. As a result, insulin levels rise, causing hypoglycemia and hunger, which encourage excess calorie consumption and, consequently, weight gain. Low glycemic index carbohydrates raise blood glucose levels more slowly, resulting in lower postprandial blood insulin levels and less hunger. This results in a more favorable lipid profile and, consequently, a reduced risk of obesity, diabetes and its complications.

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Dietary proteins are broken down to form peptides and amino acids. Proteins are essential for the maintenance, renewal, functioning and growth of tissues. However, if the body does not receive enough calories from depots (especially fats) or from food, protein can be used as an energy source.

Glycemic index of some foods

Category	Name	Index
Beans	Beans Red lentils	33 27
Bread	Soy Rye bread White bread Whole wheat	14 69
Cereals	All bran Cornflakes Oatmeal Puffed rice Wheat flakes	54 83 53 90 70
Dairy	Milk, ice cream,	34-38
Products	Yogurt
Fruits	Apples Bananas Oranges Orange juice Strawberries	61 43 32
Corn	Barley Brown rice White rice	66
Pasta	-
Potato	Instant puree (white) Mashed (white) Sweet Potatoes	86 50
Appetizers	Corn chips Oatmeal cookies Potato chips	57 56
Sugar	Fructose Glucose Honey, Refined sugar	100 91 64

The body's use of dietary protein to form tissues is net protein intake (positive nitrogen balance). In catabolic states (e.g., starvation, infection, burns) associated with tissue damage, more protein may be used than is obtained from food, resulting in a net loss of protein (negative nitrogen balance). Nitrogen balance is the best determinant of the difference between the amount of nitrogen consumed and the amount of nitrogen excreted by the body in urine and feces.

Of the 20 amino acids, 9 are essential amino acids; they are not synthesized in the body and must be obtained from food. Adults need 8 amino acids, and children from 0 to 1 year additionally require histidine.

At normal weight, the need for dietary protein is related to the growth rate, which decreases from infancy to adulthood. The protein requirement decreases from 2.2 g/kg in 3-month-old infants to 1.2 kg/g in 5-year-olds and 0.8 kg/g in adults. The protein requirement corresponds to the requirement for essential amino acids. Adults who want to reduce muscle mass require minimal amounts of protein.

The amino acid composition of proteins varies widely. Biological value reflects the similarity of the amino acid composition of the protein with the proteins of animal tissues. The most harmonious is egg white, the biological value of which is taken as 100. Animal proteins of milk and meat have a high biological value (~90); proteins of cereals and vegetables have a low biological value (-40); some other sources of protein (for example, gelatin) have a biological value of 0. The amino acid composition of individual proteins that make up the diet determines the overall biological value of the diet. According to the RDA [recommended daily allowance (dose)], a mixed diet is recommended, having a biological value of 70.

Fats

Fats are broken down to form fatty acids and glycerol. Fats are essential for tissue growth and hormone production. Saturated fatty acids, which are found in animal fats, are solid at room temperature. Vegetable fats, with the exception of palm and coconut oils, are liquid at room temperature; they contain high concentrations of monounsaturated fatty acids or polyunsaturated fatty acids. Partial hydrogenation of unsaturated fatty acids produces trans fatty acids.

The most important (essential) fatty acids (EFAs) are -6 (p-6) linoleic and -3 (n-3) linolenic acids. Other -6 acids (e.g. arachidonic acid) and other -3 fatty acids [eicosapentaenoic acid, docosahexaenoic acid] are also necessary for the body, but they can be synthesized from EFAs.

EFAs are required for the formation of various unsaturated fatty acids (eicosanoids), including prostaglandins, thromboxanes, prostacyclins, and leukotrienes. a-3 Fatty acids reduce the risk of coronary artery disease.

The need for essential fatty acids varies with age. Adults require linoleic acid equivalent to at least 2% of total caloric needs and linolenic acid equivalent to 0.5%. Vegetable oils are rich in linoleic and linolenic acids. Oils made from saffron, sunflower, corn, soybeans, evening primrose, pumpkin, and wheat germ are rich in linoleic acid. Marine fish oils and oils made from flaxseed, pumpkin, soybeans, and hemp are rich in linolenic acid. Marine fish oils also provide large amounts of some other -3 fatty acids.

In the United States, the leading dietary source of trans fatty acids is hydrogenated vegetable oil. Trans fatty acids increase LDL cholesterol and decrease HDL cholesterol; they also independently increase the risk of coronary artery disease.

Macronutrients

Na, Cl, K, Ca, P and Mg are required by the body in relatively large quantities daily (see Tables 1-3, 1-4 and 5-2).

Water. Water is considered a macronutrient because its requirement for energy expenditure is 1 ml/kcal (0.24 ml/kJ), or approximately 2500 ml/day. Water requirements vary with fever; in warm or cold climates; and in high or low humidity.

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Microelements

Vitamins and minerals as microelements are required in small quantities.

Water-soluble vitamins are vitamin C (ascorbic acid) and the eight elements of the vitamin B complex: thiamine (vitamin B1), riboflavin (vitamin B2 ₎, niacin, pyridoxine (vitamin B6 ₎, folic acid, cobalamin (vitamin B12), biotin and pantothenic acid.

Fat-soluble vitamins include retinol (vitamin A), cholecalciferol or ergocalciferol (vitamin D), alpha-tocopherol (vitamin E), and phylloquinone and menaquinone (vitamin K). Only vitamins A, E, and B accumulate in case of significant changes in the body.

Essential trace minerals include iron, iodine, zinc, chromium, selenium, manganese, molybdenum, and copper. Except for chromium, each is a component of enzymes or hormones involved in metabolism. With the exception of iron and zinc, trace mineral deficiencies are rare in industrialized countries.

The importance of other minerals for humans (e.g. aluminum, arsenic, boron, cobalt, fluorine, nickel, silicon, vanadium) has not been proven. Fluorine, although not an essential microelement, is involved in the prevention of caries by forming a composite with Ca, which stabilizes the mineral matrix of teeth. All microelements are toxic in large quantities, and some of them (arsenic, nickel, and chromium) can cause cancer.

Other food substances

The typical composition of food consumed daily by humans contains more than 100,000 chemically active substances (for example, coffee contains 1000). Of these, only 300 are nutrients and only some of them are essential. But many substances that have no nutritional value and are contained in food products are useful. For example, food additives (preservatives, emulsifiers, antioxidants, stabilizers) improve the quality of products and their stability. Microcomponents (for example, spices, indifferent substances that change the smell and taste, aroma, color, chemically active substances of plant origin and many other natural products) improve the appearance and taste of food.

Fiber, which occurs in various forms (e.g., cellulose, hemicellulose, pectin, resin), increases gastrointestinal motility, prevents constipation, and improves the course of diverticulosis. It is believed that fiber increases the rate of elimination of substances produced by colon bacteria that promote cancer development. Epidemiological studies have proven a close relationship between the development of colon cancer and low fiber intake, and a beneficial effect of fiber on functional bowel disorders, Crohn's disease (during remission), obesity, and hemorrhoids. Digestible fiber (found in fruits, vegetables, oats, barley, and beans) reduces postprandial increases in blood glucose and insulin and helps lower cholesterol.

The typical Western diet has a low fibre intake (approximately 12 g/day) due to high consumption of highly refined flour, wheat, and low intake of fruits and vegetables. Increasing fibre intake to approximately 30 g/day by consuming more vegetables, fruits and high fibre cereals is strongly recommended.