It's been known for some time that infants who are fed formula usually gain more weight than babies who are breast-fed. A recent study suggests that this depends on the type of formula an infant is fed.
Specifically, the study found that infants who were fed pre-digested proteins in the form of protein hydrolysate-based formula gained less weight than infants fed cow's milk based formula.
The weight gain seen in cow milk-fed infants was accelerated -- faster than the rate normally seen with breast milk.
Protein hydrolysate formulas are most often fed to infants who cannot tolerate the intact proteins found in other infant formulas.
A major reason for the difference in weight gain was that infants fed protein hydolysate formula drank less at a meal than those fed cow milk formula. One interpretation of these results is that infants fed the hydrolysate formula are behaving normally while those on cow milk formula are being introduced to overeating at a very early age.
In adults, one signal that the body is full comes when digested protein from a meal enters the intestine. When a meal contains pre-digested proteins, these enter the intestine faster and the signal occurs earlier. This is thought to lead to smaller meals and lower calorie intake. The researchers believe that this is why infants fed protein hydolysate formula drank less during a feeding.
The study was of 59 infants whose parents had decided to bottle feed. The infants' weight gain and feeding behavior was followed for seven months. 35 of the infants received cow milk formula while 24 received protein hydrolysate formula. Both formulas contained the same amount of calories. Once a month, infants were weighed in the laboratory and their feedings videotaped, so the length of a meal could be determined. Meals ended when infants signaled that they were full.
Because feeding behavior while breast feeding is considered the norm, it's thought that the feeding behavior with cow milk formula constitutes overfeeding. Further studies are needed to find out why infants fed cow milk formula tend to overfeed and the long-term effects this has on their growth and health.