They are indispensable ingredients in human nutrition. Their role is very important for the proper functioning of the body. Proteins are composed of amino acids in the body and participate in the construction of tissues, hormones, and enzymes. Proteins (meat, eggs, fish) are degraded in the body into amino acids. 

Amino acids are divided into essential (those which enter our organism via food- tryptophan, lysine, phenylalanine, valine, threonine, leucine, isoleucine, etc.), and non-essential (which can be synthesized in our body- glycine, asparagine, alanine, serine, cystine, proline, etc.).

Proteins can be of animal or vegetable origin.

Milk is one of the most present food of animal origin and has a great importance in the diet of people, especially of children. Other dairy products are made of milk as well as beverages and these include sour milk, yogurt, kefir, cheese, butter, cream, sour cream and more. Milk is an ingredient of ice cream, chocolate, various types of dough and candies. It can be used sparingly and should not be combined with other foods of animal origin. In its composition, it contains casein protein, about 80%, which, on its own is digested relatively quickly, but in combination with lactose (milk sugar) and high-fat, welding time can be increased up to 8 hours. It is, therefore, not recommended as a supplement to coffee because it slows metabolism and digestion of food. Milk of plant origin, is not an adequate substitute because it contains a lot of sugar, without containing essential amino acids. People who have an allergy to lactose and casein, should completely avoid using milk or replace it, if necessary, with plant origin milk.

Sour milk is produced by the fermentation of milk over technological processes in industrial technology. There are several types of sour milk, such as yogurt, kefir and the like. Sour milk is easier to digest and is often recommended as an important ingredient in a dietary supplement.

Sour cream is obtained by collecting fat from the surface of the milk. It is rich in fat and is highly caloric kind of food, but is nevertheless a very digestible food, which is used in the diet of children and healthy people and those recovering from various ailments. It may be useful in increasing body weight (BW). Butter is made from sour cream.

Cheese is one of the high-quality food of big nutritional value. It contains a high percentage of protein, minerals, vitamins and fats (which mainly depends on the type of cheese). The proteins that are essential for growth and development can be found in cheese in a form that is easily digested, so the human organism easily gets the highest quality ingredients that are needed. Although cheese is mainly used in diets of healthy individuals, it can specially enrich feeding infants and children in developing as well as patients and people who are recovering from non-contageous diseases.

Yogurt should be consumed with a small percentage of milk fat. It contains proteins, vitamin B12, calcium, zinc. Its usage helps the preservation of intestinal flora and bowel function because it contains lactobacteria.

Delicatessen products are foods that are used in a healthy diet, but limited. It is best to consume meat products of domestic production, chicken breast, turkey breast, ham, beef ham, sirloin (with limited use of nitrates, nitrites and additives). Frankfurters, pâté, sausages should be avoided as in their production are used  grind bones, ligaments, intestine, blood vessels, intestines, skin and worst quality meat, and even added soybeans, water, starch, vegetables, salt, preservatives, emulsifiers and various extracts.

Eggs contain nutritious elements that are essential in the diet and have a favorable effect on the body. Thanks to a careful diet of livestock, eggs now have more omega-3 fatty acids, antioxidants (vitamin E and vitamin A), B vitamins, selenium, iodine, riboflavin, phosphorus, protein and manganese. Egg is a kind of food, which has the highest rate of protein of all animal origin kinds of food and should be an integral part of the menu in a healthy diet, especially egg whites. Due to the amount of cholesterol in the yolk, its implementation still has to be limited. The use of fresh eggs should be avoided because it may be contaminated with bacteria of the genus Salmonella. Frying eggs in fat should be replaced by cooking in water, poaching or roasting on a non-stick frying pan over low heat or foil pan. Any combination of eggs with meat, fish or their products increases fat and cholesterol, and therefore the atherogenic potential of food. Eggs can only be combined with vegetables and grains. The exception is called in patients with lower BMI, athletes and young children.

Plant proteins are more or less incomplete. No plant source contains all the essential amino acids in full (peas, string beans, lentils, soy, beans, grains, nuts, seeds). Regarding the entry and the combination of proteins of plant origin vegeterians should be particularly conscious in order to intake all the amino acids that are essential to the body. This can be achieved if the mushrooms are combined with integral rice or oatmeal cereals with yogurt.