Doctors and scientists have long known that formula fed babies gain weight faster, and are heavier, than breast fed babies. It’s been surmised that the differing growth rate has to do with the composition of the formula, which is cow based. Recent studies support this idea.
Researchers know that free amino acids and proteins increase satiety in adults. They wanted to see if infants had the same result. Headed by Julie Mennella, PhD, researchers at the Monell Chemical Senses Center in Philadelphia randomized 64 healthy term infants whose mothers had already chosen formula over breast feeding. The babies received either cow’s-milk formula (Enfamil) or protein hydrolysate formula (Nutramigen) from ages 2 weeks to 7.5 months. By the end of the study, those infants who received the Nutramigen had weight-for-length and weight-for-age scores closer to normal than those infants who received the Enfamil, or an average of two pounds. One of the reasons for the faster weight gain may be the comparatively higher consumption of the cow’s-milk formula despite both formulas containing the same number of calories per ounce, as reported in the journal Pediatrics.
Excess weight gain in formula-fed babies has long been thought to be caused by mothers missing satiety cues and overfeeding their infants. “This research calls that into serious question,” Mennella said. “What we’re finding is the type of formula that infants are feeding [on] is contributing to the faster weight gain.”
“We’ve known for a long time that infants who are formula-fed gain weight at a faster rate,” Mennella reported. “These results suggest that you can’t lump formula fed infants into one group.”
She cautioned against basing formula choices on this study, calling for a need for further research. Mennella did acknowledge, however, the reality that this research could have on later growth in children. “Emerging evidence is informing us that this early rate of growth during the first year of life can have long-term consequences, including increasing the risk for the development of obesity, diabetes, metabolic syndrome, and a variety of other diseases,” she said in an interview.
Formula’s based on cow milk, such as Enfamil, are used by more than 75% of infants who are not breast fed. More expensive, hypoallergenic protein hydrolysate formulas are most often reserved for infants who react poorly to cow milk formula.