Macronutrients include proteins, fats and carbohydrates.

Macronutrients are organic compounds which are put into our body in relatively large quantities (grams) and serve as an energy source but also have other important functions.

  • fats have the highest energy value, since 1 g of fats contains 9 kcal (37 kJ) of energy;
  • one gram of proteins contains 4 kcal (17 kJ);
  • one gram of carbohydrates also contains 4 kcal (17 kJ);
  • one gram of alcohol provides 7 kcal (29 kJ) during the oxidation, but it is not considered a nutrient due to an adverse effect on physical growth, development and regeneration.
Food energy density gives us the number of kilocalories per 1 gram of food or meal. Recommended meal energy density for a normally fed person is from 1 to 1.5 kcal/g (4.2 to 6.3 kJ/g).

If a meal contains more than 2.5 kcal/g (10.5 kJ/g), it may represent a risk factor for excessive weight gain and obesity. Including foods with low energy value in the meals (e.g. vegetables, fruit), the meals' energy density is successfully reduced.

The recommended intake of total fats for healthy adults is 30 % of the daily energy intake. Long-term intake of total fats in adults over 40 % of daily energy intake is proven harmful to health, representing a risk factor for
  • arteriosclerosis,
  • different types of cancer, especially cancer of the intestine and rectum and
  • obesity.
Fat intake during illness and reconvalescence, as well as in the elderly: 30 - 50 % energy from non-protein sources, depending on the individual patient's tolerance for carbohydrate and fat. Saturated fatty acids (mainly animal fats) in consumed quantities larger than recommended, are harmful. Excessive consumption of saturated fats represents a risk factor for cardiovascular diseases, however they are important as a source of excess energy in cancer risk. The proportion of saturated fatty acids should come to maximum one third of all fats consumed. Saturated fatty acids also cause increased levels of LDL (bad) cholesterol in blood.

The unsaturated fatty acids include
  • polyunsaturated (linoleic, linolenic and arachidonic fatty acid) and
  • monounsaturated fatty acids, such as oleic acid (18 carbon atoms).
Unsaturated fatty acids reduce the risk of cardiovascular diseases and should therefore represent two-thirds of all fats consumed in the daily diet. Polyunsaturated fatty acids decrease LDL levels as well as HDL levels in blood, while the monounsaturated oleic acid only reduces LDL, but not HDL cholesterol. Polyunsaturated fatty acids should contribute up to 10 % of the daily energy intake. Monounsaturated fatty acids have an important role in preventing cardiovascular diseases, so their recommended intake is higher than 10 % of the daily energy intake.
Essential fatty acids (omega-3 and omega-6) can not be synthesized by the body itself. They are important for the growth and development of the brain, nervous system, retina and they cooperate in the synthesis of tissue hormones. They are also necessary for normal functioning of the immune system, so their absense increases the chances of infection and inflammatory processes. Recommended proportion of omega-3 fatty acids in a healty diet is 0.5 %, while the recommended proportion of omega-6 fatty acids is 2.5 % of the daily energy intake. In terms of health protection it is important to have the proper ratio of omega-6 and omega-3 fatty acids (omega-6: omega-3 =5:1). Omega-3 fatty acids are found primarily in fatty, cold water fish, fish oil, nuts, algae, oils from seeds and nuts and green leafy vegetables. Omega-6 fatty acids are found in sunflower and corn germ oil. Many studies have shown that eating foods rich in omega-3 fatty acids is associated with reducing the risk of coronary artery disease, high blood pressure and cancer. 
However, trans fatty acids can be health-threatening. They occur naturally in small amounts in fat, milk products and meat of ruminants or as a by-product of the process of partial hydrogenation, physical refining or frying liquid vegetable oils with unsaturated fatty acids (usually corn). The foods of natural origin have a 2-3 % share of trans fatty acids in total fatty acids, while in the industrial food this share is up to 60 %. Otherwise the quantity and type of trans fatty acids arising from partial hydrogenation, physical refining or frying, depends on temperature, pressure and duration of hydrogenation or refining and frying. Since trans fatty acids provide longer durabilty period of a food, they are often found in margarine, biscuits, cakes, ice cream, frozen potatoes and fast food. They are also found in foods that are heat-treated by frying or roasting (above 150 ˚C), because unsaturated fatty acids with double bonds (e.g. in sunflower oil or corn germ oil) oxidize at high temperatures and thus form isomers of trans fatty acids. Research results have shown that besides saturated fatty acids, also trans fatty acids have a bad influence on the amount of LDL cholesterol in blood, and also cause an increased amount of total fats. Thus trans fatty acids should be consumed in very limited quantities and their content should not exceed 1 % of the daily energy intake. This means that the daily meal with an energy value of e.g. 2000-3000 kcal should not include more than 2.2 - 3.3 g of trans fatty acids.

Proteins supply the body with amino acids and other nitrogen compounds that are necessary to produce the body's own proteins and other metabolically active substances. Proteins are important as the body can not grow, develop or regenerate without them. The protein needs vary by age but they are essential for life. There are nine indispensable (essential) amino acids which must be provided in the diet:
  • histidine,
  • isoleucine,
  • leucine,
  • lysine,
  • methionine,
  • phenylalanine,
  • threonine,
  • tryptophan and
  • valine,
and they must be obtained from food. Studies indicate that no histidine in the diet causes reduction of histidine in plasma and reduction of haemoglobin synthesis. Children and adolescents are recommended a minimum daily intake of 0.9 to 1.0 g of proteins per kilogram of body weight per day, according to their age.
The experimentally determined average adult needs for proteins of high biological value (eggs, milk, meat, fish) are 0.6 grams of proteins per kilogram of body weight per day. The biological value of proteins is the ratio between the available and the total digested and absorbed proteins. The daily diet provides proteins of plant origin which on average have a lower biological value, so the recommended protein intake is 0.8 g per kg body weight per day. Protein intake should represent 10 to 15 % of daily energy intake by age group, but not more than 20 % of daily energy intake.
The needs for protein during illness and reconvalescence, as well as in elderly people, are
1 - 1.5 g/kg body weight/day

Foods of animal origin, such as meat, fish, eggs, cheese, milk, are a rich source of protein. However, there are also some foods of plant origin which contain more protein, especially legumes (e.g. beans, peas, soybeans). Proteins of animal origin are found in meat (choose lean pieces of meat, poultry without skin), meat products, fish, seafood, eggs, milk, cheese and curd cheese. A rich source of proteins of plant origin are whole grain cereals and cereal products, legumes, nuts and soy. 
Nutritional values of protein foods of animal or plant origin complement each other and only combined they have a high biological value and available energy value.
Consuming too much proteins can slow down your metabolism, so exceeding the recommended daily amounts in the diet is unnecessary and may even be harmful. Excessive consumption of animal proteins is also associated with higher intake of saturated fat. It should be noted that foods of animal origin are often high in fat, especially saturated fatty acids and cholesterol. Numerous studies have shown that an additional protein intake in excess of 2.5 grams of protein per kg body weight per day, does not increase muscle mass or strength. It is important to include quality proteins in the diet which can be used effectively by the organism. Degradation of body protein increases during exercise, if carbohydrate reserves are low.

Carbohydrates provide the body mostly with energy, however, their ingredients are included in each body cell. Carbohydrates are the main nutrients that provides energy to the body. There are simple and complex carbohydrates. 
On one hand, simple carbohydrates include
  • monosaccharides (glucose, fructose, mannose and galactose) and
  • disaccharides (sucrose, lactose, maltose).
They are quickly digested, provide a fast source of energy and rapid secretion of insulin.
On the other hand, complex carbohydrates are polysaccharides (glycogen, starch and fiber).
The recommended intake of carbohydrates in the daily diet is at least 50 % of daily energy intake. Especially carbohydrate foods containing essential nutrients and dietary fiber are recommended. A very large intake of carbohydrates (more than 400-500 g/day in younger adults) can cause an increased synthesis of saturated fatty acids from glucose (on a small scale also from fructose) which are stored in fatty tissue. 
Simple sugars should not contribute more than 10 % of the daily energy intake and are best digested among the carbohydrates, also causing a rapid increase in insulin. They are found in kitchen sugar, honey, chocolate, sweets and sweet drinks; however, they are naturally present in fruits. If a person needs 2000 kcal per day, simple sugars should contribute up to 200 kcal of energy. One gram of sugar contains 4 kcal which represents about 50 grams of total simple sugars per day. Excess consumption of simple sugars is a major risk factor for overweight and obesity. Kitchen sugar does not contain essential nutrients and increases energy density of meals.
The impact of carbohydrate foods on increased blood glucose levels is evaluated upon glycemic index (GI). GI is a parameter that describes how fast the carbohydrates are absorbed into the blood after consumed, compared with pure glucose. The consumption of foods with high GI results in more rapid and higher increases in blood glucose level and causes increased secretion of insulin. Inhibition of the endocrine pancreas, which secretes insulin, can be seen in chronically increased blood glucose and insulin levels which can lead to impaired glucose metabolism and insulin resistance. 
The advantage of complex carbohydrates lies in higher levels of dietary fiber. Dietary fiber in a healthy and balanced diet is very important because it reduces the GI value of food/meal and has a beneficial effect on digestion. Dietary fiber is a substance of plant origin for which the human digestive tract does not have the proper enzymes to digest it and therefore remains undigested and is excreted as such. Dietary fiber generally has no energy value available, but it influences various important functions in the gastrointestinal tract. An orientation value for dietary fiber intake of adults is about 12.5 g/1000 kcal for women (if a woman daily needs e.g. 2000 kcal, then her recommended fiber intake is 25 g) and 10 g/1000 kcal for men. Recommended dietary fiber intake for children is around 10 g/1000 kcal. However, xcessive dietary fiber intake partly reduces the absorption of nutrients in the gastrointestinal tract, which should also be taken into account when planning diets, especially in children and the elderly. Dietary fibre can prevent many diseases and functional disorders. The most important are
  • constipation,
  • colon diverticulosis,
  • colon cancer,
  • gallstones,
  • overweight,
  • high cholesterol in the blood,
  • diabetes and
  • arteriosclerosis.
Fiber belongs to the protective substances, reduces the energy density of food, slows gastric emptying, while promoting digestion in the small and large intestine. There are soluble fiber, such as β-glucans, pectins, gums and partially hemicellulose, which are found in pome fruit, oranges, grapefruit, peas, lentils, soybeans, vegetables, and insoluble fiber, such as cellulose, hemicellulose and lignin, which are mainly found in whole grain cereal products.