Breast milk contains more than 700 types of bacteria, found a new study, which also revealed that the bacterial composition of a mother’s milk changes as her baby grows and that a woman’s body size and the kind of birth she has affect the bacteria that appear in her milk.

The study offers insights into the health benefits of breast milk and hints at how companies might eventually make more nutritious infant formulas.

“If the bacterial composition of human breast milk has co-evolved to maximize the infant’s metabolic efficiency and to optimally stimulate the immune system, a skewed microbial milk composition might have important consequences for the infant’s health,” the researchers wrote in the American Journal of Clinical Nutrition. “Those potential consequences would need to be evaluated for future recommendations in child nutrition.”

Breast milk is full of nutrients that protect babies from infections and help their guts cultivate populations of beneficial bacteria. To better understand the breast-milk microbiome, Spanish researchers collected milk from 18 women at three times: within two days of giving birth (when they were producing just colostrum), one month later and six months after delivery.

Through DNA analysis, the team revealed more than 700 species of microbes, more than they were expecting. Colostrum was the most diverse. After that, microbiomes changed in composition.

When the scientists separated women by body mass index (BMI), they found fewer bacteria species in the colostrum and early milk of moms who were overweight or who gained more than the recommended amount of weight during their pregnancies. It’s possible that microbiome transfer from mother to infant can also transfer a predisposition to obesity.

Women who delivered vaginally and those who had unplanned cesarean sections had more diverse colonies in their milk compared to women whose C-sections were planned. That suggests that a woman’s hormones during labor affect her milk in unexpected ways, which could also affect a baby’s risk for asthma and related diseases.

Still to be determined are what all those bacteria do and where they come from in the first place. More details might eventually lead to better strategies for keeping infants healthy.

“If the breast milk bacteria discovered in this study were important for the development of the immune system,” the researchers said in a press release, “its addition to infant formula could decrease the risk of allergies, asthma and autoimmune diseases.”

Photo: iStockPhoto