Breast Milk. Types, Composition, and Benefits

Breast milk is the best food for your baby because it is fully aligned with the baby’s biology. It is easy to digest and contains the right amount of essential nutrients and other factors contributing to the child’s immune health and development.

Key takeaways:
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    Breastmilk is the best food for the baby, providing the optimal amounts of macro and micronutrients, hormones, growth factors, and other molecules.
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    Each group of nutrients from breast milk has specific health benefits.
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    Both the mother and the baby benefit from breastfeeding.

The American Academy of Pediatrics recommends breastfeeding until the baby is 1 year of age and even longer, with complimentary solid foods introduced to the diet after 6 months of age.

The three types of breast milk

Breast milk composition changes over time, matching the baby’s nutritional needs. The composition is also different between term and preterm babies.

Colostrum is the first fluid made in the first three days of life. It is produced in small amounts, thick and sticky. Colostrum is lower in fat and higher in proteins compared with mature milk. It is also rich in compounds that support immune health like lactoferrin, white blood cells and secretory IgA.

From day five to 14, breast milk is called transitional milk. It is creamier due to its higher content in fat and is also full of nutrients and bioactive ingredients. Mature milk is the milk formed from four weeks onwards. It is rich in macro and micronutrients, hormones, enzymes, growth factors and live cells needed to support the baby’s growth and development.

Mature breast milk composition

Human breast milk contains about 87-88% water, 7% carbohydrates, 1% protein and roughly 3.8% fats. Typically, mature milk contains about 65–70 kcal per 100 mL of energy, with about half of the total caloric energy coming from fats and 40% from carbohydrates. The composition varies depending on the mother’s diet, mother’s overall health and other factors.

  • Proteins. The most abundant proteins in breast milk are whey and casein. Proteins are essential for the growth, development and proper function of all cells and the body's tissues. Certain proteins also play important roles in fighting infections. For example, whey contains lactoferrin, which can inhibit iron-dependent bacteria and fungi. Another whey protein component called secretory IgA helps protect the baby from viruses and bacteria and may also help prevent allergies.
  • Lactose, also known as milk sugar, is the main source of carbohydrates. Lactose plays an essential role in nutrition and the development of the baby’s gut flora. Furthermore, gut flora supports immune system function, digestion, and brain health.
  • Fat content varies significantly, with lower amounts found in the full milk lactating breast to higher amounts in the more drained lactating breast. Breast milk contains different fats, including triglycerides, essential fatty acids, linoleic acid and alpha-linolenic acid. The content of omega 3 fatty acids depends on the mother's diet- the milk is richer in omega 3s if the mother consumes more of them in the diet or takes supplements. Fats provide energy for the baby and are important for the development of the brain, eyes, immune system, and growth. Fats also help the baby absorb fat-soluble vitamins A, D, E and K.

The mother’s diet highly influences the vitamin content of breast milk. For this reason, healthcare providers recommend a well-balanced nutritious diet and to continue supplementing with prenatal vitamins during lactation. Babies may require vitamin D and K supplements if exclusively breastfed because breast milk may not provide sufficient amounts. Lactating mothers who are vegan or vegetarian need additional supplementation with B vitamins, particularly B6, B12, and folate.

Breast milk contains 20 minerals, including iron, copper and zinc, with higher amounts in colostrum. Unlike vitamins, the content of minerals in the breastmilk is not significantly affected by the mother’s diet or supplement intake. Iron supplements are not recommended before 4-6 months of age. After six months of age, iron-enriched foods can be introduced into the diet.

  • Breast milk contains various compounds, including hormones like insulin, leptin and ghrelin, which regulate the metabolism and support immune health.
  • Growth factors play key roles in blood vessels, digestive system, brain and hormonal balance development.
  • Among other bodily fluids, breast milk is one of the richest sources of microRNAs. MicroRNAs are biologically active compounds that play essential roles in immune health, growth and development.

Breast milk is not sterile

In the past, it was believed that breast milk was sterile. However, research from the last two decades found that milk contains a microbial community, including plenty of friendly bacteria. A recent study identified 820 microbial species, including some strains of Lactobacillus and Bifidobacterium, in the human milk microbiota. Scientists are still investigating how these bacteria accumulate in the milk and their role in the baby's health.

Breast milk benefits

Benefits for the baby. According to the American Academy of Pediatrics, children who are breastfed experience better health, with a decreased risk of ear infections, diarrhea, respiratory tract infections, eczema, asthma, celiac disease, Crohn’s disease, ulcerative colitis, diabetes type 1 or 2, leukemia, excess weight during childhood, necrotising enterocolitis and Sudden Infant Death Syndrome (SIDS).

Benefits for the mother. Lactating mothers also experience health benefits. Compared with women who fed their babies with infant formula, those who breastfed have a lower risk of breast, ovarian, thyroid, and endometrial, decreased risk of developing high blood pressure, type 2 diabetes, rheumatoid arthritis, and heavy periods. Lactating also helps the mother bond with the baby.

Breast milk offers the perfect combination of macronutrients (proteins, fats, carbohydrates), micronutrients, various hormones, growth factors and other molecules. While infant formulas mimic the macro and micronutrient content, the living cells and other biologically active compounds found only in breast milk make the difference.

Lactation consultants can help support all women who are interested in breastfeeding. Milk banks and donor milk are good options for those unable to breastfeed.


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