April 5, 2004 -- What makes children picky eaters? Why do some kids only eat bland foods while others scarf down curry? Likely, it's due to flavors they are exposed to very early, before they reach 4 months old -- and even while they are in the womb.
Flavor preferences take shape during sensitive periods in an infant's development and serve as the foundation for lifelong food habits, writes lead researcher Julie A. Mennella, PhD, with the Monell Chemical Senses Center in Philadelphia. Her study appears in the April issue of Pediatrics.
The study "may help us understand early factors involved in human food preferences and diet choice, an area with many important health implications," writes Mennella. "We can explore these early influences systematically by studying infants who are breastfeeding, as well as babies whose parents have decided to formula-feed."
Infant Formula Provides Insights
Most babies get milk-based infant formulas like Enfamil or Similac, which are often described as being "sour and cereal-like." But for babies with milk or protein intolerance or allergy, or with colic, there are hydrolyzed protein-based formulas like Alimentum, Pregestimil, and Nutramigen - which have a bitter and sour taste, unpleasant smell, and horrible aftertaste, explains Mennella.
In earlier studies, Mennella has shown that 4- or 5-year-old children fed Nutramigen during their infancy had a more positive response to the formula several years later.
Her current study involved 53 babies, each fed either Nutramigen or Enfamil for seven months. Two more groups of infants were given three months of Nutramigen, introduced at different times, with four months of Enfamil.
At the end of seven months, all were given both types of infant formula, as well as a third hydrolyzed formula, Alimentum. Researchers videotaped the babies' responses to each of the formulas to get a better idea of their reactions, which illustrated their sensory response to each infant formula.
Which formula the infants accepted depended on which they had tasted before -- and when they first tasted it:
- Those who had tasted Nutramigen before responded to both Nutramigen and Alimentum as if they were very acceptable. Babies fed Nutramigen longer than three months accepted it even more.
- Those babies who had never gotten the bad-tasting Nutramigen strongly rejected it and Alimentum. The babies' facial expressions showed that taste and smell were factors driving their responses.
While it's known that newborns reject bitter, sour tastes, her study shows that this rejection does not occur until after 4 months of age, she writes. The "bitter" taste receptors may not mature until the infant is several months old.
The studies highlight a fundamental feature of dietary learning among mammals, she writes. Humans and other animals taste their mothers' diet while in the amniotic fluid of the womb. After they are born, infants are again exposed to her diet if they nurse.
Flavors common to an ethnic group are therefore experienced early in life, she writes.
"Because we know that flavor preferences established early in life track into later childhood, eating habits in the growing child may begin to be established long before the introduction of solid food," Mennella says in a news release.