Congenital and experiential factors in the development of human flavor preferences.

Experimental modifications of congenitally based human responses to taste stimuli are being evaluated during the first few years of life. Sweet- and salty-tasting substances form the focus of our research. Prior studies indicate that human preference for sweet substances is innate whereas need-free acceptance of salty-tasting substances has been thought to be learned. Our recent studies indicate that ingestive expression of the innate preference for sweet tasting substances may be subject to modification quite early in life, although the effects of experiences are specific to the particular food context in which sweet is experienced. A sense of what should and should not be sweet, rather than a generalized hedonic responsiveness to sweetness itself, appears to be shaped through dietary experience. In studies with salt (NaCl), our data reveal two distinct changes in the acceptance of near-isotonic salt solutions during early development. The first is a shift from indifference to relative (to water) preference which appears around 4 months of age. We hypothesize this is due to maturation rather than learning. The second shift is one from relative acceptance to relative rejection which is variable in its time of appearance (although it occurs by 2 to 3 years of age in populations we have studied) and is probably due in part to the development of neophobia in conjunction with a lack of experience with salty water. We suggest that in the absence of need, the appeal of both sweet- and salty-tasting substances, in large part at least, is innately determined. Dietary experience during development determines the appropriate food-related contexts for these appealing tastes.