KIDS
May 5, 2016

Fertilizer for Babies

Breast milk is a complex mix of over 200 sugars that gets newborns off to a strong start.

Human breast milk has the most complex chemical composition of any mammal's milk. It contains more than 200 different types of sugar molecules; the milk from a cow or mouse only contains about 30 to 50 different sugars.

Advances in gene sequencing technologies will make it easier for researchers to study the composition of human breast milk and its role in culturing helpful bacteria in babies' intestinal tracts.

The importance of these molecules to infants' nutrition and development is just becoming clear. A new review of the scientific findings on breast milk reveals a wide range of benefits and the possibility that breast milk may be the ultimate personalized medicine.

Infants are born without any bacteria in their gut. Yet within weeks of birth, their digestive tract is colonized by billions of bacteria. This microbial diversity appears to offer infants a big advantage.

The sugar molecules in milk encourage the growth of the bacteria that make up the infant's microbiome. “It’s like a seeding ground, and breast milk is the fertilizer,” Thierry Hennet, co-author of the review, said in a statement.

Breast milk also helps support the development of a baby’s immune system. This process is established early. Breast milk secreted in the first few days after birth, the colostrum, is rich in antibodies that provide protection against different disease-causing organisms.

During the first few weeks of life, anti-inflammatory molecules in breast milk, cytokines, contribute to the development of immunity on the mucosal membranes found in organs that link the newborn to the external environment, such as the lungs, intestines and urinary tract. This immunity is selective. It provides protection against infectious organisms, but allows the baby's body to tolerate the non-toxic environmental substances that come its way.

After about the first month, the composition of breast milk changes from primarily supporting immunity to supporting infant growth. Its fat content increases, and so do the levels of hormones that control satiety, fat storage, growth and blood sugar levels. At the same time, levels of maternal antibodies decrease by more than 90 percent. The diversity of sugar molecules also decreases.

Breast milk reduces infant mortality rates and the risk of gut and respiratory infections, but there is little scientific evidence suggesting longer-term benefits. Breast milk serves many important functions in newborns and infants, and children do thrive without it.

For this reason scientists need to be cautious about making recommendations about what is best for newborns, said Hennet, a physiologist at the University of Zurich. Even though breast milk is the product of millions of years of evolution, and has the optimal composition of nutrients, “The question becomes, ‘How long does the newborn really need this supply?’ We feel families should make that decision, not scientists.”

Advances in gene sequencing technologies will make it easier for researchers to study the composition of human breast milk. The authors believe the next few years will bring a better understanding of the hormones in human breast milk and the role of breast milk in culturing bacteria in a baby’s intestinal tract.

The article is published online in Trends in Biochemical Sciences.

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