The findings of the study suggest that the protein composition of infant formulas, may have implications for the risk of developing obesity, diabetes and other metabolic diseases later in life.
Published in Pediatrics, the new study found that the rate of weight gain for infants fed a formula containing protein hydrolysate was comparable to national values for breast-fed infants,. In contrast, infants fed a cow's milk formula gained weight at a greater rate than the same breast milk standards.
"Events early in life have long-term consequences on health and one of the most significant influences is early growth rate," said study lead author Dr Julie Mennella, a developmental psychobiologist at the Monell Chemical Senses Center, U.S.A. "We already know that formula-fed babies gain more weight than breast-fed babies. But we didn't know whether this was true for all types of formula."
The right formula
Rapid rates of growth during the first year increase the risk for later obesity, metabolic syndrome, and mortality from cardiovascular disease, which leads some to speculate that interventions designed to reduce the incidence and severity of disease should begin during infancy.
Using breastfed infants as the gold standard, past research has suggested that infants who are fed formula weigh more and have greater risk for later obesity.
Whilst most infant formulas are cow's milk-based, other choices include soy-based and protein hydrolysate-based formulas. Protein hydrolysate formulas contain pre-digested proteins and typically are fed to infants who cannot tolerate the intact proteins in other formulas.
The authors said that in adults, these pre-digested proteins are believed to act in the intestine to initiate the end of a meal – thus leading to smaller meals and intake of fewer calories.
“Recent evidence suggests that, relative to intact proteins, hydrolyzed proteins are absorbed and metabolized in a way that promotes greater satiation ... we conducted a randomized study on healthy, formula-fed infants to determine whether growth patterns and feeding behaviours differ on the basis of formula type,” said Mannella and colleagues.
Infants whose parents had already decided to bottle-feed were randomly assigned at two weeks of age to feed either a cow's milk-based formula (35 infants) or a protein hydrolysate formula (24 infants) for seven months.
According to the authors, both formulas contained the same amount of calories – but the hydrolysate formula had more protein, including greater amounts of small peptides and free amino acids.
The infants were weighed once each month in the laboratory, where they also were videotaped consuming a meal of the assigned formula.
Over the seven months of the study, Mennella and colleagues observed that infants fed the protein hydrolysate gained weight at a slower rate than infants fed cow milk formula. They noted that linear growth, or length, did not differ between the two groups, demonstrating that the differences in growth were specifically attributable to weight.
"All formulas are not alike," said Mennella. "These two formulas have the same amount of calories, but differ considerably in terms of how they influence infant growth."
"One of the reasons the protein hydrolysate infants had similar growth patterns to breast-fed infants, who are the gold standard, is that they consumed less formula during a feed as compared to infants fed cow's milk formula" said Mennella. "The next question to ask is: Why do infants on cow's milk formula overfeed?"
Mennella and colleagues added that their findings highlight a need to understand the long-term influences of infant formula composition on feeding behaviours, growth, and metabolic health.
However, they added that the longer-term effects of hydrolyzed protein diets, which are relatively new in the human food supply – but are growing in use – also need to be investigated.
Published online ahead of print, doi: 10.1542/peds.2010-1675
“Differential Growth Patterns Among Healthy Infants Fed Protein Hydrolysate or Cow-Milk Formulas”
Authors: J.A. Mennella, A.K. Ventura, G.K. Beauchamp