There are many contributors to childhood weight gain — diet, inactivity, genes — but a study released on Dec. 27 in Pediatrics identifies another potential cause: certain types of baby formula.
Researchers from the Monell Chemical Senses Center recruited 56 mothers with new infants to test two types of infant formula. The women, who had already decided to feed their children formula, were split into two groups: For seven months, starting when the babies were two weeks old, 32 of the babies got traditional formula made from cow’s milk — the most popular kind available; 24 received a “hypoallergenic” formula called protein hydrolysate formula (PHF), which contains predigested proteins that are easier on infants’ digestive tracts. (More on Time.com: How Your Dad’s Diet Affects Your Weight)
All the infants were regularly weighed and measured, and were also videotaped while feeding. Early on, researchers found that the traditional formula-fed group was gaining more weight more quickly than the PHF group; the babies getting cow’s-milk formula had significantly higher weights per length by 2.5 months. After just 3.5 months, researchers found that the cow’s-milk formula group also weighed significantly more for their age, compared with PHF-fed babies, who weighed on average the same as breast-fed infants.
What’s more, the cow’s-milk formula group remained heavier throughout the study, even though all the infants began eating solid foods at about the same time. It’s not clear why cow’s-milk formula may contribute to increased weight, but the researchers speculate that the type and amount of protein in PHF may make babies feel fuller faster, or that babies dislike the taste of PHF and eat less. The Los Angeles Times reported:
[Researchers] speculate that the free amino acids in the pre-digested formula did a better job of stimulating receptors in the mouth and gut that signal to the brain that the stomach is full and it’s time to stop eating. Though babies in both groups spent about the same amount of time eating at each feeding (between 11 and 12 minutes), the babies on the PHF formula drank less during that time before pushing the bottle away.
“Because dietary and nutritional programming can have long-term consequences in terms of later development of obesity, diabetes, and other diseases, it is imperative that we learn more about the long-term consequences of the early growth differences caused by environmental triggers, such as those associated with infant formulas, and how and why they differ from breast-feeding, which is the optimal mode of feeding,” the researchers wrote.