Understanding breastfeeding supply and demand

A nursing baby with an insatiable appetite can cause a first-time mom to doubt more than just her sanity. But, a simple lesson in supply and demand can provide reassurance that her hungry infant is doing exactly as nature intended.

"Sudden increases in infant appetite and feeding frequency should not alarm breastfeeding moms," said Darryl Hadsell, a Ph.D. scientist who studies mammary cell response to lactation-related hormones and nutrient availability at the CNRC.

"Increased demand sets up a biological chain-reaction that ensures a mother's milk production keeps pace with her infant's needs for growth and development," he said.

According to Hadsell, the laws of physics require that the concentration of lactose, the milk sugar, remains constant in breast milk. This means that a mother's body naturally increases milk volume when it steps up production of lactose.

"Lactose production inside milk-producing cells is tied to the synthesis of a key protein that helps turn blood sugar into lactose," Hadsell said. The production of this protein, called alpha-lactalbumin, is under the control of hormones that are released in response to nursing.

Increased feeding frequency causes more of a hormone called prolactin to be released into a mother's bloodstream. This hormone, along with insulin and substances called glucocorticoids, turn on alpha-lactalbumin production, which causes more lactose to be made and leads to greater milk volume.

According to Hadsell, this cascade of events, from demanding infant to hormone-induced increased milk volume, continues until milk supply meets demand. Once it does, infant hunger, feeding frequency--and family life--generally return to normal.

However, a new mom who isn't aware of this natural progression might doubt her body's ability to meet her hungry child's needs and begin supplementing with formula. While this might give temporary relief, it can intensify breastfeeding problems in the long run.

"Feeding formula interrupts the nursing cycle and reduces breast emptying, which permits a build up of another protein involved in regulating milk production called the Feedback Inhibitor of Lactation, or FIL," Hadsell said.

A build-up of FIL reduces the sensitivity of milk-producing cells to prolactin, which cuts alpha-lactalbumin and lactose production. "In the short-run, the effects of FIL on milk volume are reversible if exclusive breastfeeding is soon resumed. But, if the situation becomes chronic, FIL is thought to trigger an actual reduction in the number of breast cells capable of producing milk," he said. "While this is normal during the weaning period, it is not desirable otherwise."

"A new mother can trust her body to respond to her infant's changing nutritional needs if she simply allows her infant to determine the timing and duration of feedings," Hadsell said.

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