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Several pieces of work have shown that the flavors of the foods consumed by the mother may be transferred into the amniotic fluid and the milk [17–19], but this phenomenon is variable and not yet fully known [10, 11].

Nevertheless, the exposure to specific flavors in utero is associated to a higher attraction for the specific food odor at birth [17], to a higher acceptance of the specific food the infant was exposed to in utero when this food is offered at the beginning of complementary feeding [20], as well as to a higher acceptance of a similarly flavored food later in childhood [21].

In a similar fashion, the exposure to flavors in mother’s milk is associated to a higher acceptance of the specific food the infant was exposed to in mother’s milk when this food is offered at the beginning of complementary feeding [20] and to a positive effect of breastfeeding on acceptance of a new food, even in the absence of a specific flavor exposure [22]. This work suggests that the variety of flavor exposure in breast milk may be key and not only the specific exposure to a given flavor.

To expand this building knowledge on the effect of early taste and flavor exposure (i.e., dietary exposure to a variety of tastes in foods), in the OPALINE cohort we wondered about the effect of exposure to specific tastes in the context of milk feeding. It has been described that breast milk contains much more glutamate than formula milk, a compound that is associated with the umami taste. In this context, we observed that infants who were breastfed longer had a higher preference for the umami taste at the age of 6 months [23]. Moreover, concomitant with the introduction of complementary foods which are characterized by a variety of tastes, taste differential reactivity (within-subject variability across tastes; the higher the score, the greater is the difference in reaction of the infant to the tastes) clearly increased [14].

In order to develop our understanding of infant dietary taste exposure, we developed a method to evaluate the taste properties of the diet by describing extensively the intensities of the tastes of all the foods consumed monthly by infants relying on data from “food taste databases” [24]. The application of this method showed that the exposure of French infants to tastes was dominated by exposure to sweet taste over the first year, as illustrated in Figure 1 (in relation to the sweet taste of milk and a number of foods introduced after the initiation of complementary feeding) [25]. We expanded these findings by comparing the dietary exposure to sweet taste and fattiness [26]. They both increased during the first year in relation to the introduction of complementary foods in the child’s diet, but exposure to sweetness increases more rapidly than exposure to fattiness.

However, we have not shown any specific associations between dietary exposure to each taste and acceptance of each taste measured in water, as explained above [27]. The longer-term associations between early exposure to taste and further taste preferences are currently being explored in the OPALINE cohort.

Concerning olfactory exposure, we have found that at 8 months of age only, positive correlations were found between liking of some unpleasant odors and early exposure to these odors through the mother’s diet. However, no correlations were found between infants’ liking of the pleasant odors and early exposure to the foods bearing these odors. This study highlights that early exposure to unpleasant food odors may increase subsequent liking (or reduce subsequent dislike) of these food odors at least until the age of 8 months [28].

Fig. 1. Dietary exposure of infants to the 5 primary tastes over the first year based on dietary data collected in the French OPALINE cohort (adapted from Schwartz et al. [25] with permission).

The originality of the OPALINE study was to evaluate the effect of early odor exposure on the infant through the mother’s spontaneous consumption of a wide spectrum of foods without asking mothers to consume one target food bearing a specific odor quality in sizeable amounts. Such “ecological” research regarding the influence of prenatal and dietary taste and flavor exposure on the establishment of preferences for foods with similar tastes and flavors is still in its beginning. More studies in different cultural contexts were the flavor experience is likely to be contrasted are needed to more completely understand these early imprinting phenomena.