"This research may help us to understand early factors involved in human food preference and diet choice, an area with many important health implications," says lead author Julie Mennella of the Monell Chemical Senses Center in Philadelphia. "We can explore these early influences systematically by studying infants who are breastfeeding, as well as babies whose parents have decided to formula-feed." In the latest study, the researchers used two types of infant formulas: a standard milk-based formula and a second so-called protein hydrolysate formula, in which the proteins are broken down to aid in digestion. The former is quite bland whereas the latter is bitter and sour and quite disagreeable to most adults.
The team looked at 53 babies who were fed either just one of the formula types or a specific combination of the two. After seven months, the children were fed while being videotaped and the scientists analyzed their reactions to different formulas. Those babies who had never tasted the hydrolysate formula reacted strongly to it, showing their displeasure with distinct facial expressions (see top image, above). Subjects that had fed only on hydrolysate formula or had eaten it at some time previously, in contrast, were much more likely to enjoy it (see bottom image, above). "Because we know that flavor preferences established early in life track into childhood," Mennella explains, "eating habits in the growing child may begin to be established long before the introduction of solid food."