The Bigger the Bottle, the Bigger the Baby?

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CHAPEL HILL, NC – UNC School of Medicine researchers found that exclusively formula-fed babies who use larger bottles may be at risk of greater weight gain in infancy and, in turn, of obesity later in life. Data for the study was collected from the Greenlight Intervention Study, a cluster randomized trial to prevent childhood obesity at four pediatric resident clinics.

“There has been quite a bit of research around the relationship between container or plate size and food intake for adults, and we wanted to explore whether the same relationship exists early in life with bottles,” said Charles Wood, MD, MPH, lead author of the study and clinical instructor of general pediatrics and adolescent medicine at UNC-Chapel Hill.

The study, published today in the journal Pediatrics, shows that infants who are regularly fed from a large formula bottle (greater than 6 oz.) by the time of their 2-month well visit exhibited greater weight gain and weight-for-length size than infants of comparable age. Wood said that the weight gain was independent of other factors.

“Growth in infancy is complex,” he said, “but bottle size may be a risk factor for rapid weight gain and, in turn, later obesity.”

This study followed 379 exclusively formula fed infants from the Greenlight study starting at their 2-month well visits through their 6-month well visit. Investigators had parents bring in the bottle they were using and show how much formula was being given to the infant at feeding time or choose a bottle similar to the ones they typically used from samples the researchers had on site.

By the time of the 6-month visit, infants fed formula exclusively from large bottles had gained nearly half a pound (7.4 oz.) more than those who were fed with smaller bottles.

Wood said weight gain varies widely among infants, but it is important for parents to establish an understanding of appropriate hunger and fullness cues, whether the child is receiving formula, breastmilk, or a combination of both.

“The exciting part of this study is to think about the fact that this relationship between weight gain and container size may start really young – younger than we thought,” said senior author Eliana Perrin, MD, MPH, professor of pediatrics the UNC School of Medicine, one of five principal investigators of the NIH-funded Greenlight Intervention Study.

“This gives us some novel things to think about when we are trying to prevent obesity — a major public health problem,” Perrin said. “A lot of us eat more when our food is on larger plates — even when we are not hungry for it. The large size of the bottle combined with pressuring the baby to finish it may not be as healthy for our babies as remembering that we all have hungry days and less hungry days.”

Wood, Perrin, and their team previously reported that larger bottles are associated with more daily intake of formula. But they said that more research is needed to completely understand the link between bottle feeding and obesity risk to help inform interventions.

“There is a whole host of bottle sizes and types out there that are marketed to parents, and for some, a bigger bottle may be chosen because of cost, availability, or other factors,” Wood said. “Regardless of the bottle size, adults who are feeding the infant need to have a ‘bidirectional’ relationship during each feeding. That means not being distracted by the phone or the television, and watching for cues that the baby is full.”

Infant weight gain is complex, but the research team said it’s important to study the trajectory of growth and making sure children are tracking along a healthy curve.

“What our study helps uncover is that the size of the bottle may be one of several ways we can optimize healthy weight gain in the first year of life,” said Wood.

Wood’s team and their collaborators plan to follow up with additional studies around infant feeding behavior.

This research was funded by the National Institutes of Health. Charles L. Wood, M.D., M.P.H, is a NRSA Primary Care Research Fellow at the Cecil G. Sheps Center for Health Services Research and a clinical instructor for the division of general pediatrics and adolescent medicine at the UNC School of Medicine; and Eliana M. Perrin, MD, MPH is a professor of pediatrics in the division of general pediatrics and adolescent medicine in the department of pediatrics at the UNC School of Medicine and a pediatrician at North Carolina Children’s Hospital.

Their co-authors include: Asheley Skinner, PhD, of the Duke Clinical Research Institute and department of medicine at Duke University; Shonna Yin, MD, MS, of NYU School of Medicine Pediatrics; Russell Rothman, MD, MPP, of Vanderbilt University Medical Center, Center for Health Services Research; Lee Sanders, MD, MPH of Stanford University Pediatrics; Alan Delamater, PhD, of University of Miami Pediatrics.