Sensitive period in flavor learning: effects of duration of exposure to formula flavors on food likes during infancy

Abstract

Background & aims: Emerging research has revealed the existence of periods in which the developing brain has heightened sensitivity to environmental influences. We discovered a sensitive period, <4 months of age, when exposure to the flavor of extensively hydrolyzed protein hydrolysate formulas (ePHF) determines its hedonic tone. This formula has pronounced bitter, sour, and savory tastes compared to cow-milk-based formulas (CMF). This study aimed to determine the effects of duration of exposure during the sensitive period on a food containing an exemplar of the savory flavor.

Methods: Formula-fed infants were randomized into four groups at age 0.5 months: one control group fed the CMF for 8 months, and three groups fed ePHF for 1, 3, or 8 months and CMF otherwise. When infants were 8.5 months, their acceptance of a savory and plain broth was measured.

Results: Infants fed hydrolysate formula for 3 or 8 months, but not 1 month, showed greater acceptance of the savory broth relative to the plain broth (p < 0.01) and consumed it at a faster rate (p = 0.01).

Conclusions: The duration of flavor exposure affects infants' earliest responses to foods: a 3-month exposure to ePHF shifted the hedonic tone for savory flavor.

Figure 1. Experimental groups

The groups refer to the duration (months) fed protein hydrolysate formula (ePHF; dark grey boxes) or cow milk formula (CMF; light grey boxes). The months refer to the age of the infants at the beginning of each monthly cycle and then the age of infants (8.5 months) when test meals were conducted (crosshatched bars). On 2 separate days, infants were videotaped as they fed a plain or savory broth during infant-led feeding conditions. The broth was presented in 2-ounce bottles that were an appropriate size for self feeding. The mother of the subject provided consent for use of the photograph.

Figure 2. Intake

Amount of savory broth relative to plain broth consumed by 8.5-month-old infants during infant-led feeding. Repeated measures ANOVA with a priori planned comparisons between experimental groups and CMF control indicated that infants with 3 and 8 months of exposure to ePHF consumed significantly more of savory broth relative to plain broth than control group. *Significantly different from the CMF control group, p<0.017.