The most common category of functional nutrition is fermented milk products, which normalize the intestinal microflora and increase the immune status of the human body. Fermented milk products are characterized by high biological and nutritional values. This means a high degree of balance in the amino acid composition of milk proteins, compared to the so-called ideal food protein, the amino acid composition of which meets the needs of the human body. In addition, the proteins of fermented milk products are well digested by proteolytic enzymes of the gastrointestinal tract. The main casein proteins are capable of being broken down equally well by proteolytic enzymes in their native and denatured states. The macroorganism and intestinal microflora are a relatively stable and balanced ecological system, the balance of which, on the one hand, is determined by the physiological and immunological characteristics of the macroorganism, on the other, by the species and quantitative composition of microbial associations and the diversity of their biological activity. In a normal physiological state, the relationship between the macroorganism and the microflora is symbiotic in nature, and the latter has a significant impact on the general immunity and natural resistance of the host to infections, takes an active part in the processes of digestion and the synthesis of various biologically active substances. In turn, the macroorganism regulates the composition of the intestinal microflora due to factors such as the acidity of gastric juice and the content of bile salts. Fermented dairy products are the main suppliers of probiotic microorganisms that contribute to the maintenance and restoration of human microbial ecology. Probiotic cultures that provide beneficial effects on the consumer’s body and normalize the composition and functions of the microflora of the gastrointestinal tract include such types of lacto- and bifidobacteria as Lactobacillus acidophilus, Lactobacillus casei, Bifidobacterium spp. (B. adolescentis, B. animalis ssp. lactis, B. bifidum, B. longum, B. breve).