How much weight loss is too much? Nursing researcher Diane Thulier is conducting a study that could result in new guidelines for breastfed infants.

Wrapping up this September, the year-long study is investigating whether existing standards—which now direct health care providers to recommend supplementing breast milk with formula if babies lose too much weight—could be too stringent. All breastfed babies are expected to lose some weight, usually between 5 and 7 percent of birthweight in the first week. If that number can safely be higher—Thulier suspects up to 10 percent—then doctors can delay intervening. That’s important because supplementing with formula often triggers an early end to breastfeeding and the life-long protections it offers.

“Right now, we lack good information about what is normal,” says Thulier. “I want to arm parents, doctors, and other health-care workers with updated information so that parents can relax a bit, mothers can continue to nurse their babies, and providers can have accurate guidelines.”

Previous studies have focused on the first few days of a baby’s life, and primarily tracked formula-fed infants. Thulier’s work is following the first weeks in the lives of 180 babies, drinking breast milk, formula, and a combination, at South County Hospital, Wakefield, R.I.