Nearly 20 percent of children and adolescents and 14 percent of toddlers in the United States are obese and researchers are trying to figure why. One major influence, among many possibilities, may be what a baby eats during their critical first six months of life and how it sets the stage for their continued growth. Ideally, breast milk is their only food during this critical stage. Given the importance of breast milk, School of Public Health Professor Ellen Demerath has been conducting a long-term study to analyze its complex composition and track the ways it relates to growth and weight gain.

As a part of that larger MILk study, Demerath recently published a paper in the journal Obesity measuring the levels of appetite-regulating hormones in the milk of women who had varying weight status before, during, and after pregnancy. Demerath looked at appetite-regulating hormones in breast milk because some previous research suggests that high levels of some types may interfere with the growth rate of children during their early months.

“Breast milk is complicated, and through this new research, we found its composition really does differ and it depends to some extent on the mom’s weight status,” says Demerath.

To measure the relationship between weight and hormone levels, the study team collected health record weight data and milk samples from 135 exclusively breastfeeding women participating in the long-term study.

The researchers measured three particular hormones in the milk:

• Leptin, an appetite suppressant
• Insulin, which suppresses eating as well as controls sugars entering body tissues
• Adiponectin, a hormone that has a role in appetite regulation and limits inflammation in the body

The analysis showed that obese mothers had elevated levels of leptin and insulin, and lower amounts of adiponectin in their milk. The investigation also found that leptin milk levels were higher for women with greater weight gain during pregnancy and decreased for mothers who lost weight postpartum.

According to Demerath, it’s much too early to speculate what the hormone levels mean for babies and their risk for becoming obese.

“We’re very early in the understanding of how breast milk works and differs among people,” says Demerath. “It could be that the hormone levels we found in obese mothers are beneficial to the baby. Also, the main risk may have nothing to do with the mom’s weight status, and could be driven by other factors, such as the mother’s diet quality.”

Demerath says the next step in the investigation is to follow the babies who drink the milk by measuring the amounts of hormones they consume and tracking how that relates to their growth and weight gain. She hopes to secure funding to follow the children up to age five, when they start choosing food largely on their own.