Composition and benefits of breast milk

Protein and fat components

Reduced protein load. Mature human milk contains a physiologically low protein concentration—about 1.15 g per 100 mL, which is significantly lower than in cow's milk or formulas. This protects the infant from protein overfeeding, which leads to excessive weight gain and overloads the liver and kidneys. Whey proteins predominate in qualitative composition, specifically $\alpha$-lactalbumin (25–35%). It serves as a source of essential amino acids, stimulates the growth of bifidobacteria, and improves calcium and zinc absorption.

Amino acid profile. Human milk minimizes the toxic load on the central nervous system due to reduced levels of phenylalanine, tyrosine, and threonine. At the same time, it is rich in cysteine, tryptophan, and taurine. The latter is essential for infants: it is required for the differentiation of CNS tissues and the retina, and for stabilizing cell membranes.

Fat characteristics. The concentration of polyunsaturated fatty acids (PUFAs) is 12–15 times higher than in cow's milk. PUFAs are necessary for the myelination of nerve fibers, synthesis of tissue hormones (prostaglandins), and prevention of atherosclerosis. Fats are easily digested due to a high degree of emulsification and the presence of the enzyme lipase.

Carbohydrate profile and microbiota

The primary carbohydrate of breast milk is $\beta$-lactose (80–90%). Unlike the $\alpha$-lactose of cow's milk, it performs a plastic function in brain development and stimulates calcium absorption. Part of the $\beta$-lactose reaches the colon, where it is converted into lactic acid, creating an ideal environment for the normal flora.

About 15% of carbohydrates are represented by oligosaccharides. They are not digested in the small intestine and act as a powerful prebiotic. Oligosaccharides also play the role of decoy receptors: they bind bacteria, toxins, and viruses (including rotaviruses) in the intestinal lumen, preventing them from attaching to enterocytes.

Milk itself is not sterile: it serves as a source of live bifidobacteria and lactobacilli that directly colonize the GI tract and trigger the formation of the immune system, which reliably reduces allergic sensitization.

Minerals, vitamins, and osmolarity

Breast milk has low osmolarity, which protects the excretory system. For example, the sodium concentration in it is significantly lower than in cow's milk, which reduces the risk of developing autonomic dysfunction in puberty.

The key advantage of the mineral composition is colossal bioavailability:

• Iron (Fe): 50% absorbed (vs. 20% from formulas) thanks to the transport protein lactoferrin.
• Calcium (Ca) and Phosphorus (P): their absolute quantity is small, but the proportion is ideal for assimilation.
• Copper (Cu): transported by the specific protein ceruloplasmin.

Milk contains a full spectrum of vitamins, depending on the mother's diet. However, the physiological level of vitamin D is initially low, which requires medicinal prevention of rickets in infants who are exclusively breastfed.

Immunity and digestive system maturation

Milk provides the infant with humoral and cellular defense. It contains secretory immunoglobulin A (sIgA), which creates a protective film on mucous membranes, as well as lysozyme and live macrophages, neutrophils, and lymphocytes. This reliably reduces the incidence of acute respiratory infections and acute intestinal infections.

Of particular interest is the phenomenon of microchimerism: maternal stem cells from milk are not digested, but instead penetrate the child's systemic circulation and integrate into developing organs.

Natural feeding maintains gastric secretion at a physiological level. The introduction of formulas, by contrast, forces secretion 5 times over, which disrupts the GI tract's genetic biological clock and prospectively increases the risk of gastroduodenitis, dyskinesia, and peptic ulcer disease.

Class and exam questions

What else to study on this topic

• Mechanisms of iron absorption and the role of lactoferrin
• The phenomenon of microchimerism: pathways of maternal stem cell migration
• Synthesis and functions of secretory immunoglobulin A (sIgA) in the gut
• The role of human milk oligosaccharides (HMOs) in microbiome formation

Other topics in "Chapter 3. Adaptation, Early Childhood Nutrition, Rickets"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.