Breast milk could be doing more than just nourishing a newborn -- it could also be helping them develop healthy bacteria to protect them from disease, illness and obesity.
New research from the University of Colorado Anschutz Medical Campus looked at the role of human milk hormones in the development of a baby's microbiome -- their bacterial ecosystem -- in their digestive system.
Published in the American Journal of Clinical Nutrition, it's the first study to suggest breast milk could shape an infant's microbiome.
The levels of insulin and leptin in breast milk were positively associated with a greater microbial diversity and families of bacteria in an infant's stool.
Insulin and leptin are associated with bacterial functions which help the intestine develop as a barrier against harmful toxins.
The researchers say the hormones could help protect children from chronic low-grade inflammation which can go on to develop into a number of digestive problems and diseases.
They also saw a difference in children born to obese mothers compared to those of normal weight.
Babies born to obese mothers had a significantly less gammaproteobacteria, which help intestinal development and the maturing of the microbiome.
The bacteria have been shown in mice and infants to cause a healthy amount of inflammation in the intestines which protects them from inflammatory and autoimmune disorders later in life.
Thirty babies two weeks old who were only breast-fed were studied, with the bacteria in the newborns' stool analysed. The metabolism of the bacteria was also studied.
A dozen of those were born to obese mothers, while the rest were born to mothers of normal weight.
"Just like children learn language and social cues as they grow, their digestive system learns how to regulate itself," said co-first author assistant professor Dominick Lemas.
"What we've found is that hormones in breast milk are linked to the development of infants' microbiome, potentially having long-term effects on children's intestinal and autoimmune health."
What the study suggests is the hormones bind to specific receptors in the intestines and may stimulate the body to product proteins which can kill certain types of bad bacteria. It can also stimulate intestinal cells to secrete molecules which allow good bacteria to grow.
Jed Friedman, corresponding author and professor of pediatrics at CU Anschutz, says he's interested to see whether the results of the study will help better understand what makes up a healthier immune system in infants born to obese mothers over their first year of life.
"What happens if you restore these bacteria in the infant born to an obese mother remains an open question."