It’s long been known among doctors that maternal obesity is one of the strongest predictors of childhood obesity, and new research confirms this has to do with maternal milk.

The study shows that the molecular composition of the breast milk of an expecting mother who is obese differs from that of an expecting mother at a normal weight. This difference could affect the weight of the child. Researchers think that mothers with obesity and those at normal weight have different metabolites that contribute to their children's weight composition.

This finding is significant because variations in small molecule metabolites found in breast milk are possible risk factors for childhood obesity, said the study published online in The American Journal of Clinical Nutrition.

"Childhood obesity increases risk for type 2 diabetes, and a host of other health complications. Our aim is to identify the earliest risk factors that predict obesity in children,"Dr. Elvira Isganaitis, a researcher at the Joslin Diabetes Center and study lead author, said. "We know that one of those factors is nutritional exposures in the postnatal period."

The Joslin Diabetes Center is the world’s largest diabetes research center, diabetes clinic and provider of diabetes education. It’s located in the Longwood Medical and Academic Area in Boston, Massachusetts. The study also involved researchers from the University of Oklahoma Health Sciences Center and the University of Minnesota.

There wasn't much known about the composition of human breast milk beyond basic macronutrients before 2010, study senior author Dr. David Fields, PhD, an associate professor at the University of Oklahoma Health Sciences Center and an expert in pediatric diabetes, said.

"Our research digs deeper into the composition of breast milk, beyond simple carbohydrates, protein and fat."

Researchers analyzed breast milk content and infant body measures (fat and muscle) at both one month and six months of age in 35 mother-infant pairs. Mothers were classified by pre-pregnancy body mass index (BMI) less than 25 (normal) or greater than 25 (overweight/obese).

Dr. Isganaitis and collaborators analyzed the concentration of 275 individual small molecule metabolites in breast milk using “metabolomics analyses” (a technique for large-scale studies of small molecules involved in metabolism).

Their aim was to identify the molecular features of breast milk according to the mother's weight status (normal versus overweight/obese) and then to determine if any differences predicted excess weight in the first months of the infant's life.

They found that when a child reaches 1 month old, overweight or obese, and normal weight mothers had 10 metabolites that distinguished their breast milk. Three of those were complex carbohydrates that could affect gut microbiota. By the time the child is 6 months old, the study showed 20 different metabolites in overweight and normal weight mothers.

"Our findings suggest that a specific mix of factors -- nucleotide derivatives and complex carbohydrates -- could be therapeutic targets to improve the profile of breast milk and possibly protect children from obesity," Dr. Isganaitis said.

Obese mothers also had milk adenine, which is linked to weight gain in babies.

Researchers say knowing how a mother's breast milk could affect a child's weight may give health professionals better insight into how to advise parents on better diet or exercise habits.

They emphasized that breastfeeding should be promoted and supported. What researchers want is to identify the metabolic pathways that allow breast milk to be beneficial in terms of infant weight gain, and other child health outcomes.

"The hope is that this data could also inform ways to make baby formula more protective in terms of future childhood obesity risk,” Dr. Isganaitis said.