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Background Repeated exposure has been found to be an effective strategy to increase acceptability of foods in older children and adults, but little is known about its effectiveness in the birth to 24-mo population. Objectives This systematic review was conducted to examine the effects of repeated exposure to a single or multiple foods on acceptance of those or other foods among infants and toddlers. Methods A search was conducted for peer-reviewed articles related to food acceptability, flavor, taste, and infants and toddlers in 12 databases (e.g., PubMed, Embase, Cochrane, and CINAHL) with a date range of January 1980 to July 2017. The Nutrition Evidence Library (NEL) Bias Assessment Tool was used to assess potential bias in the included studies, and the NESR grading rubric was used to grade evidence supporting the conclusion statement. Results From the 10,844 references obtained, 21 studies (19 controlled trials and 2 longitudinal cohort studies) published from 1980 to 2015 were included in this review. Moderate evidence indicates that tasting a single vegetable or fruit or multiple vegetable(s) or fruit(s) 1 food per day for 8-10 or more days is likely to increase acceptability of an exposed food (indicated by an increase in intake or faster rate of feeding after comparison with before the exposure period) in infants and toddlers 4-24 mo old. The effect of repeated exposure on acceptability is likely to generalize to other foods within the same food category but not foods from a different food category. Findings are based on the effects of repeated exposure to mostly vegetables with some findings on repeated exposure to fruits. Conclusion This review advances the understanding of early food experiences and the development of food acceptability. Additional research is needed using diverse foods and textures with a focus on the transition to table foods.

Background The impact of feeding a slightly sweet nutrient supplement early in life on later sweet taste preference is unknown. Objective We tested the hypothesis that the level of sucrose most preferred by 4–6-y-old children exposed to a slightly sweet lipid-based nutrient supplement (LNS) early in life would not be higher than that of children never exposed to LNS. Design We followed up children born to women (n = 1,320) who participated in a randomized trial in Ghana. In one group, LNS was provided to women on a daily basis during pregnancy and the first 6 mo postpartum and to their infants from age 6 to 18 mo (LNS group). The control groups received daily iron and folic acid or multiple micronutrients during pregnancy and the first 6 mo postpartum, with no infant supplementation (non-LNS group). At age 4–6 y, we randomly selected a subsample of children (n = 775) to assess the concentration of sucrose most preferred using the Monell 2-series, forced-choice, paired-comparison tracking procedure. We compared LNS with non-LNS group differences using a noninferiority margin of 5% weight/volume (wt/vol). Results Of the 624 children tested, most (61%) provided reliable responses. Among all children, the mean ± SD sucrose solution most preferred (% wt/vol) was 14.6 ± 8.6 (LNS group 14.9 ± 8.7; non-LNS group 14.2 ± 8.4). However, among children with reliable responses, it was 17.0 ± 10.2 (LNS group 17.5 ± 10.4; non-LNS group 16.5 ± 10.0). The upper level of the 95% CI of the difference between groups did not exceed the noninferiority margin in either the full sample or those with reliable responses, indicating that the LNS group did not have a higher sweet preference than the non-LNS group. Conclusion Exposure to a slightly sweet nutrient supplement early in life did not increase the level of sweet taste most preferred during childhood. This trial was registered at clinicaltrials.gov as NCT00970866.

Background: What lactating mothers eat flavors breast milk and, in turn, modifies their infants' acceptance of similarly flavored foods.Objective: We sought to determine the effects of the timing and duration of eating a variety of vegetables during breastfeeding on the liking of vegetables in both members of the dyad.Design: We conducted a randomized controlled study of 97 mother-infant dyads. Lactating mothers drank vegetable, beet, celery, and carrot juices for 1 mo beginning at 0.5, 1.5, or 2.5 mo postpartum or for 3 mo beginning at 0.5 mo postpartum. The control group drank equal volumes of water and avoided drinking the juices. Mothers rated the tastes of the juices and self-reported dietary intakes at each monthly visit (0.5-4.5 mo). After weaning, when 7.9 mo of age, infants' acceptance of plain, carrot-flavor (exposed flavor), and broccoli-flavor (nonexposed flavor) cereals was assessed on separate days.Results: The timing of exposure affected the acceptance of the carrot flavor that did not generalize to the novel broccoli flavor. A relatively brief experience (1 mo) with vegetable flavors in mothers' milk, starting at 0.5 mo postpartum, was sufficient to shift the hedonic tone, which resulted in a faster rate of eating carrot-flavored cereal than that in infants who were exposed during subsequent months or not at all. One month of exposure had a greater effect than 3 mo of exposure or no exposure. Regardless of when exposure occurred, infants were less likely to display facial expressions of distaste initially when eating the carrot cereal. Over time, mothers liked the tastes of carrot, beet, and celery juices more, but no changes in dietary intake of vegetables were observed.Conclusions: Early life may be an optimum time for both infants and their mothers to learn to like the taste of healthy foods. More research is needed to facilitate the liking and eating of these foods by mothers, which will, in turn, increase the likelihood of their feeding these foods to their children. This trial was registered at clinicaltrials.gov as NCT01667549.

Background: Alleles of the receptor gene TAS2R38 are responsible in part for the variation in bitter taste perception of 6-n-propylthiouracil (PROP) and structurally similar compounds (eg, glucosinolates in cruciferous vegetables). At low concentrations, people with the PAV (“taster” amino acid sequence) form of TAS2R38 perceive these bitter compounds, whereas most with the AVI (“nontaster” amino acid sequence) form do not; heterozygotes (PAV/AVI) show the widest range of bitter perception. Objectives: The objectives were to examine individual differences in expression of PAV-TAS2R38 messenger RNA (mRNA) among heterozygotes, to test the hypotheses that the abundance of allele-specific gene expression accounts for the variation in human bitter taste perception, and to relate to dietary intake of bitter-tasting beverages and foods. Design: Heterozygous individuals (n = 22) provided psychophysical evaluation of the bitterness of PROP, glucosinolate-containing broccoli juice, non–glucosinolate-containing carrot juice, and several bitter non-TAS2R38 ligands as well as dietary recalls. Fungiform taste papillae were examined for allele-specific TAS2R38 expression by using quantitative polymerase chain reaction. Results: PAV-TAS2R38 mRNA expression was measured in 18 of 22 heterozygous subjects. Relative expression varied widely and positively correlated with ratings of bitterness intensity of PROP (P = 0.007) and broccoli juice (P = 0.004) but not of the control solutions carrot juice (P = 0.26), NaCl (P = 0.68), caffeine (P = 0.24), or urea (P = 0.47). Expression amounts were related to self-reported recent and habitual caffeine intake (P = 0.060, P = 0.005); vegetable intake was too low to analyze. Conclusions: We provide evidence that PAV-TAS2R38 expression amount correlates with individual differences in bitter sensory perception and diet. The nature of this correlation calls for additional research on the molecular mechanisms associated with some individual differences in taste perception and food intake. The trial was registered at clinicaltrials.gov as {"type":"clinical-trial","attrs":{"text":"NCT01399944","term_id":"NCT01399944"}}NCT01399944.

Background: We recently discovered that infants randomly assigned to a formula high in free amino acids (extensive protein hydrolysate formula; ePHF) during infancy consumed less formula to satiation and gained less weight than did infants fed an isocaloric formula low in free amino acids (cow milk formula; CMF). Objective: Because ePHF and CMF differ markedly in concentrations of free glutamate, we tested the hypothesis that the higher glutamate concentrations in ePHF promote satiation and satiety. Design: In this counterbalanced, within-subject study, infants ,4 mo of age (n = 30) visited our laboratory for 3 sets of 2 consecutive infant-led formula meals over 3 test days. Infants were fed 1 of 3 isocaloric formulas during each first meal: CMF, ePHF, or CMF with added free glutamate to approximate concentrations in ePHF (CMF+glu). When infants signaled hunger again, they were fed a second meal of CMF. From these data, we calculated satiety ratios for each of the 3 formulas by dividing the intermeal interval by the amount of formula consumed during that particular first meal. Results: Infants consumed significantly less CMF+glu (P , 0.02) and ePHF (P , 0.04) than CMF during the first meals. They also showed greater levels of satiety after consuming CMF+glu or ePHF: satiety ratios for CMF+glu (P , 0.03) and ePHF (P , 0.05) were significantly higher than for CMF. Conclusion: These findings suggest a role of free glutamate in infant intake regulation and call into question the claim that formula feeding impairs infants’ abilities to self regulate energy intake. This trial was registered at clinicaltrials.gov as NCT00957892. Am J Clin Nutr 2012;95:875‐81.

Background: By using the response to protein hydrolysate formula (PHF) as a model system, we discovered the existence of a sensitive period, before 4 mo, when exposure determines the hedonic tone to flavors. Objective: We aimed to characterize the timing and duration of this sensitive period. Design: Healthy infants, whose parents had chosen formula feeding, were randomly assigned into 1 of 6 groups at age 0.5 mo: 2 control groups, one fed cow milk–based formula (CMF) and the other fed PHF for 7 mo; 2 groups fed PHF for either 1 or 3 mo beginning at 1.5 mo and CMF otherwise; and 2 groups fed PHF for 1 mo beginning at either 2.5 or 3.5 mo and CMF otherwise. Brief access taste tests were conducted monthly, and complete “meals” of both formulas occurred at the end of the study. Results: Three months of PHF exposure led to acceptance similar to that at 1 mo of exposure. Although these infants were more accepting than were infants with no exposure, they were less accepting than were infants with 7 mo of exposure, which suggests a dosing effect. The time when flavor experiences began was also significant. Among infants exposed to PHF for 1 mo, those who were first fed PHF at 3.5 mo rejected PHF relative to CMF more than did infants exposed at younger ages. Conclusion: The general principles observed are likely of broader significance, indicating a fundamental feature of mammalian development and reflecting the importance of familiarizing infants with flavors that their mothers consume and transmit to breast milk. This trial was registered at clinicaltrials.gov as {"type":"clinical-trial","attrs":{"text":"NCT00994747","term_id":"NCT00994747"}}NCT00994747.

Background: Research in humans and animal models suggests that acceptance of solid foods by infants during weaning is enhanced by early experiences with flavor variety. Objective: We tested the hypotheses that the acceptance of novel foods by formula-fed infants could be facilitated by providing the infants with a variety of flavors at the time when beikost is first introduced and that, contrary to medical lore, infants who had previously consumed fruit would be less likely to reject vegetables when first introduced than would infants without such an experience. Design: The infants’ acceptance of a novel vegetable (pureed carrot) and a novel meat (pureed chicken) was evaluated after a 9-d exposure period in 3 groups of infants, some of whom had previously consumed fruit. During the home-exposure period, one group was fed only carrots, the target vegetable; a second group was fed only potatoes, a vegetable that differed in flavor from carrots; and a third group was fed a variety of vegetables that did not include carrots. Results: Infants fed either carrots or a variety of vegetables, but not those fed potatoes, ate significantly more of the carrots after the exposure period. Exposure to a variety of vegetables also facilitated the acceptance of the novel food, pureed chicken, and daily experience with fruit enhanced the infants’ initial acceptance of carrots. Conclusion: These findings are the first experimental evidence to indicate that exposure to a variety of flavors enhances acceptance of novel foods in human infants. Am J Clin Nutr 2001;73:1080‐5.