In the study, "Bottle Size and Weight Gain in Formula-Fed Infants," which is published in the journal Pediatrics, researchers looked at 298 infants whose parents said they were strictly formula feeding at their two month well visits. What they found was that using a larger bottle predicted 0.16 kg more weight gain and a larger weight-for-length size by their six-month appointments.
How much is 0.16 kg? It's equivalent to 0.3527396 lbs., which doesn't sound like much. So does it matter? As lead researcher Charles Wood, M.D., M.P.H. NRSA, a chief resident/fellows & education at the Division of General Pediatrics and Adolescent Medicine at UNC School of Medicine in Chapel Hill, North Carolina, explained to Parents.com, "A 0.16 kg weight gain is highly dependent on the infant's growth and growth trajectory, so this will depend on each individual infant."
And let's keep in mind, babies are uber-tiny!
But it's not the actual number that's significant here. Research has already shown that formula-fed infants are at a higher risk for being obese later in life. This study indicates that the mode of feeding is important, not just the milk type. In fact, other research has actually pointed to the fact that infants who are fed breast milk via a bottle tend to gain more weight, as well. (This particular research did not look at babies who were fed breast milk in a bottle).
The takeaway for parents here is that a child's risk factors for gaining excessive amounts of weight—in a society where 1 out of 3 kids is considered obese, according to KidsHealth.org—start at birth. Again, this study showed when parents used a larger bottle at the two month visit, a baby was more likely to have increased weight gain by the six month appointment, suggesting overfeeding is taking place.
It's worth noting the study looked at mostly ethnic minority groups; 41 percent of the babies were black, 35 percent were Hispanic, and most were from households earning less than $20,000 per year, where the parents did not go to college. This is significant because we know babies in lower income areas are fed formula at higher rates, and are also more likely to be obese later in life, lending support to the notion that reducing a baby's bottle size may be a first step in preventing a lifetime of excessive weight gain.
Still, Dr. Wood cautions parents, "A larger bottle may be a factor involved in overfeeding and increased weight gain in the first months of life, but it is important to understand that there are likely other factors involved, and we need to study this in more detail in the future."
Melissa Willets is a writer/blogger and a mom. Follow her on Twitter (@Spitupnsuburbs), where she chronicles her love of exercising and drinking coffee, but never simultaneously.