The study, published in The American Journal of Clinical Nutrition, notes that while previous research has shown that maternal obesity strongly affects a baby's risk for becoming overweight, but until now scientists have been unsure about how this risk of fatness is transmitted.
Led by corresponding author Professor Michael Goran from the University of Southern Carolina, the new research identified variations in complex carbohydrates found in breast milk - called human milk oligosaccharides (HMOs) – that are linked to variations in infant growth and obesity.
The study is the first to identify variations in HMOs as a possible protective or risk factor for obesity, said the team.
“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,” said Goran.
"The infant's first exposure to nutrition sets the stage either for increased or decreased risk of obesity,” commented first author Tanya Alderete - who noted that because they cannot be digested, HMOs accumulate in the colon and can act as prebiotics that play a role in shaping a baby's gut microbiome.
"How the gut microbiome develops will have a long-term influence on obesity and health risk," said Goran. "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."
The team noted that while genetics play a role in HMO composition, the factors that influence variation in the composition of breast milk are not yet known – adding that a mothers diet likely has a role.
"HMOs are the third most abundant component in human breast milk," said Lars Bode, a study co-author from the University of California San Diego and president-elect of the International Society for Research in Human Milk and Lactation. "The concentrations of these complex sugars are higher than the concentrations of all human breast milk proteins combined."
"To our knowledge, there are no studies examining how HMOs are affected by the mothers' diet," said Alderete. "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."
The study examined 25 mother-infant pairs and looked at breast milk and infant measures at ages one month and six months to test whether differences in the composition of human milk oligosaccharides (HMOs) correlate with infant growth and body composition.
Goran and his colleagues defined breastfeeding as not using infant formula and noted that some babies may have been introduced to solid food, which would have contributed to growth and body composition.
The study revealed that the specific mix of HMOs in breast milk can make a big difference – suggesting that the composition of individual breast milk may be more important in predicting obesity than even the mother's obesity and her weight gain during pregnancy.
"At 6 months of age, higher breast milk levels of LNFPII [lacto-N-fucopentaose II] and DSLNT [disialyl-lacto-N-tetraose] were each associated with approximately 1 pound of greater fat mass," revealed Alderete, who added that other HMOs were protective at 6 months.
“Increased amounts of a HMO called LNFPI [N-fucopentaose I] in breast milk was associated with about a 1-pound lower infant weight and fat mass,” she said.
The team noted that the study could not determine cause and effect between HMO composition and obesity, partially because it did not have any measures beyond 6 months of age – adding that further research, including longer studies, are now needed.
"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 formulae," said Goran – noting that current infant formula does not contain any HMOs.
Source: The American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.115.115451
“Associations between human milk oligosaccharides and infant body composition in the first 6 mo of life”
Authors: Tanya L Alderete, Chloe Autran, et al