Breast milk from the bottle may not have as many benefits for a baby's weight as feeding straight from the breast, a new study suggests.
The researchers found what many others have: Overall, breastfed babies tended to have a healthier weight than those who were formula-fed.
However, babies given pumped breast milk did not benefit as much as those who fed from the breast.
Researchers stressed that breast milk, in any form, is better than formula. But they said the findings support the notion that the method of feeding matters, too.
Many women, particularly in the United States, have to pump breast milk when they return to work, noted lead researcher Meghan Azad, an assistant professor of pediatrics and child health at the University of Manitoba in Canada.
"The message here is not that pumping is 'bad' or 'wrong,' " she said. "It's better than formula-feeding."
However, Azad explained, there are reasons why feeding at the breast might promote the healthiest rate of weight gain.
For one, she said, breast milk contains a range of "interesting enzymes and hormones." And it's possible that their activity is depleted when pumped milk is refrigerated.
In addition, Azad said, it's thought that babies learn to "self-regulate" food intake when they nurse at mom's breast. In contrast, when parents bottle-feed, they often take charge -- encouraging their baby to finish the bottle.
Dr. Joan Meek is chair of the American Academy of Pediatrics section on breastfeeding. She said the AAP recommends exclusive breastfeeding for about six months. Once the baby starts on solid foods, Meek said, breastfeeding can continue "for as long mother and child desire."
She agreed that there are reasons direct breastfeeding is ideal -- and the new findings support that. But practically speaking, Meek added, many women have to pump.
"The lack of paid maternity leave policies in the U.S. can be a barrier for mothers who work outside the home," Meek said. "Certainly for those mothers, their [pumped] breast milk is still the next best thing to direct breastfeeding."
The findings, published online Sept. 24 in the journal Pediatrics, are based on more than 2,500 mother-infant pairs.
On average, the study found, babies who were still exclusively breastfed at 6 months had the healthiest weight by the age of 12 months. By comparison, babies who were no longer exclusively breastfed at 6 months had a threefold greater risk of being overweight by their first birthday.
However, when the researchers looked at moms' feeding methods, they found that babies given pumped breast milk tended to weigh a little more than those who fed from the breast.
It all suggests that direct breastfeeding is better for a "healthy weight trajectory," said Dr. Alison Holmes, a pediatrician at Dartmouth-Hitchcock Medical Center in Hanover, N.H.
Like Meek, Holmes acknowledged the practical barriers. So she recommended that any time working moms are with their baby, they opt for the direct route rather than the bottle.
Holmes also pointed to a side benefit: "There's less time spent washing dishes."
The study also looked at the effects of solid food introduction on babies' weight. In general, it found, when babies started on solids before the age of 5 months, their weight gain was on the rapid side.
But there was no sign that introducing solids at 5 months, rather than 6 months, spurred especially quick weight gain.
"So introducing solids at that age may be OK, if that's what your baby wants," Azad said.
When it comes to starting solids, Holmes said, there seems to be a window that's best for babies' overall health.
"Introducing solid foods sometime after the 5-month mark, but before the 7-month mark is healthiest in terms of balancing the benefits of healthy weight gain, allergy prevention and infectious disease prevention," she said.
To Azad, the findings have implications not just for parents, but for policies on paid maternity leave.
"This is saying, you can't just give moms a breast pump and think you've solved the problem," Azad said.