A newborn’s risk of becoming obese could be determined by his mother’s breast milk, according to new findings from the University of Southern California. The study, published in The American Journal of Clinical Nutrition, is the first to identify how different carbohydrates in breast milk are linked to infant growth and obesity. Mothers therefore could be protecting or increasing the risk of their newborn becoming obese each time they breastfeed.

"Early life experiences related to the environment and different feeding modalities contribute to obesity," said the study’s co-author Michael Goran, a professor of preventive medicine and pediatrics at USC’s School of Medicine, in a press release. "But typically we think of obesity risk kicking in after weaning — the timing of introduction to solid foods, early exposures to sugary beverages. Clearly there is something going on before weaning even in babies who are exclusively breastfed."

For the study, the research team examined 25 mothers’ breast milk and their 1- to 6-month-old infants. They measured different levels of carbohydrates found in their breast milk called "human milk oligosaccharides" (HMOs), which are known to play a role in the development of an infant’s immune system. But now researchers have discovered different types of HMOs may be able to protect a baby from becoming obese or increase the risk by the time they’re 6 months of age.

Researchers combed through 71 previous reports on the overall effects of breastfeeding on obesity, and found that breastfeeding was able to reduce excess weight and obesity by about 10 percent. But when they took a closer look, they found a specific mix of HMOs in breast milk can mean the difference between a child born with a weight problem or not despite the mother’s weight. In fact, researchers believe the kind of carbohydrates found in breast milk influence the baby’s weight more than the mother’s own weight gain or obesity during pregnancy.

HMOs became the focus throughout all of the studies because they’re the third most abundant ingredient in human breast milk and are found in higher concentrations than proteins. HMOs can’t be digested, so they accumulate in the colon and shape the way a baby’s gut microbiome forms, which is the population of bacteria in the intestine. This gave research teams from the dozens of past studies an opportunity to measure the baby’s HMO levels from their poopy diaper.

Babies who were 6 months of age and had higher levels of two different carbohydrates (LBFPII and DSLNT) were more likely to have one pound more of fat than babies with normal or low levels of those carbohydrates. Meanwhile, other HMOs, like one called LNFPI, had a protective effect and were linked with a one pound lower of fat.

"How the gut microbiome develops will have a long-term influence on obesity and health risk," Goran said. "These compounds that are not being digested go straight into the infant's gut and act as prebiotics. They act as fuel for microbes in the gut and help them grow and become diverse."

Gut microbiome influence the immune system, brain function, and weight because of the influence they have on insulin, appetite, and metabolism. An unbalanced mix of gut microbes can lead to obesity and inflammation, says Dr. Gerard Mullin, a gastroenterologist and nutritionist at Johns Hopkins Hospital. Consuming a diet high in fat and refined carbs favors fat accumulation and obesity. According to these new findings, gut microbiomes may start building and influencing the future of a person as young as 6 months old.

"Ultimately what we would like to be able to do is identify which of the HMOs are most important for obesity protection and then use that as a supplement that can be given to the breastfeeding infant and added to infant formula," Goran said.

Currently, HMOs are not added into infant formula. Using them to influence how a baby begins to develop their unique microbiome community may lead to a future of feeding babies anti-obesity concoctions. In the last 30 years, childhood obesity has more than doubled in children and quadrupled in adolescents, according to the Centers for Disease Control and Prevention. Intervening and improving their diets earlier could set the stage for a healthier upbringing.

"The infant's first exposure to nutrition sets the stage either for increased or decreased risk of obesity," said the study’s lead author Tanya Alderete, a postdoctoral researcher at USC’s School of Medicine, in a press release. "It would be very interesting if dietary sugar or fat consumption were found to be related to HMOs. That is something we hope to explore in future studies."

Source: Alderete T and Goran MI, et al. The American Journal of Clinical Nutrition. 2015.