LAUSR

Objectives Infants are predisposed to reject bitter tastes in order to prevent the ingestion of toxic substances. Thus, some infants may respond to bitter flavors with a physiological response consistent with how they respond to environmental threat, with implications for their behavior. Respiratory sinus arrhythmia (RSA) is an index of parasympathetic regulation of the heart, which decreases in response to challenging or threatening stimuli (i.e., RSA withdrawal), allowing the individual to engage in a fight or flight response (Porges, 2007). Here, we examined whether RSA withdrawal (RSAW) was associated with infants' behavioral reactions to bitter green vegetable purées. Methods Infants/toddlers (n = 106; 57 males) tasted a familiar food (rice cereal) and a novel food (kale purees) offered by their caregivers (94% mothers) during a laboratory visit. Trained coders watched video recordings to tally infants' rejections (e.g., head turns, spoon swatting) and rate their degree of acceptance (4-point scale; 0 = refusal to 3 = anticipation). Three disposable electrodes were placed on the infants' chest areas prior to feeding to measure heart rate (R-waves). Data were edited and used to calculate RSA values in 15-s epochs using CardioBatch Plus (Brain-Body Center, University of North Carolina, Chapel Hill). RSAW scores were calculated by subtracting average RSA during the kale tasting from average RSA during the familiar food baseline task; higher scores indicated greater RSAW. Multiple regression models were used to examine associations between RSAW and infants' reactions to the kale (rejections, acceptance) after controlling for child age (months) and the amount of time since they last ate (minutes). Results Regression models predicting novel food rejection (F(3,82) = 8.78, R2 = .49) and acceptance (F(3,83) = 9.81, R2 = .51) were significant. After controlling for covariates, greater RSAW was associated with more rejection behaviors (β = .21, P = .03) and less acceptance (β = -.24, P = .01). Conclusions Infants who demonstrated greater RSAW during the kale feeding also responded to the kale with a behavioral "fight" response-greater rejection of the food. This study provides preliminary evidence that when infants reject bitter green vegetables, their physiological responses reflect a reaction to environmental threat. Funding Sources The Sugar Association.