In a study released this month in Pediatrics, “Bottle size and weight gain in Formula-fed infants,” Dr. Charles Wood et al. (peds.2015-4538) look at the very interesting question of whether bottle size impacts weight gain in formula-fed infants. The authors use data from “Greenlight”, a cluster randomized trial conducted at 4 pediatric residents clinics.
“Greenlight” enrolled predominantly low-income minority parents and infants at 2 months of age, and included a targeted obesity prevention intervention that did not specifically address bottle size. As part of “Greenlight”, the study team asked very specific questions about feeding, obtained reliable weight and length measures at 2 and 6 months, and actually confirmed the size of the bottle as “most like the one … use[d] to feed.” So, what is a “big bottle”? The authors established >6 ounce size as a “big” bottle – any 2 month old who is regularly chugging 6 ounces per feed is a pretty big (or “good” as many parents would say!) eater.
And yes, bottle size at 2 months of age did make a difference in weight for age and weight for length at 6 months of age, even after adjustment for multiple confounders. The methods and results sections are an easy read, and the study is well explained--please see the details for the whole story.
What are the take home points for pediatricians? Should we ask all parents to check their 6 and 8 ounce bottles at registration so we can confiscate them and substitute smaller bottles? It’s unlikely that this strategy will be effective, but this study certainly opens up some interesting new approaches. Bottle size may be a valuable “talking point” for anticipatory guidance among parents who are formula feeding. And similarly, I wonder if nipple flow speed will be another key variable to consider in the “battle of the [infant] bulge?”
Could “slow flow nipples” be as important to 6 month growth measures, and potentially to subsequent obesity, as smaller bottle size? Little data is available, and industry marketing claims are not helpful. In a recent study, milk flow rate was highly variable between advertised brands, and nipple name was uninformative (Pados BF et al. MCN Am J Matern Child Nurs. 2016 Mar 22). Clearly we need additional data in order to consider any recommendations.
Another arena pediatricians might want to consider is focused guidance on not just “hunger cues,” but on “satiety cues.” Hunger cues have taken on greater importance as part of the Baby Friendly Hospital Initiative with Step 8 (of the Ten Steps to Successful Breastfeeding) encouraging feeding on demand, which is only possible if parents are well educated that crying is a late sign of hunger, and that lip smacking, alerting and rooting signify early hunger (https://www.babyfriendlyusa.org/about-us/baby-friendly-hospital-initiative/the-ten-steps). So how do you know if your baby is getting full? We can coach parents that slowed and shorter sucking bursts, milk dribbling from the corner of the mouth, closed eyes, and relaxed and open hands let the parent know that it’s time to remove the bottle, rather than urging the baby to go for the “homerun” of an empty bottle.
Finally the excellent study of Woodet al again emphasizes that breastfeeding is a public health imperative. Despite the possibility of residual confounding, high quality studies show a 13% reduction in risk of obesity with breastfeeding (summary OR 0.87 [95% CI 0.76- 0.99]- Horta BL et al. Acta Paediatr Suppl. 2015; 104: 30-7.) And although the study of Woods et al specifically addressed formula fed infants, we know from the work of Li et al (Arch Pediatr Adolesc Med. 2012;166:431-6) that babies who are fed breastmilk by bottle gain more weight than those fed exclusively at the breast, so breast milk provision is also sensitive to method of feeding. Read and “digest” this article of Woods and colleagues that has implications for all of us who care for infants whether we are parents or health care professionals!