taste differential reactivity, revealing the importance of olfaction in neophobic reactions. Further studies are ongoing to examine the long-term effect of early taste and flavor exposure on food preferences.
© 2019 Nestlé Nutrition Institute, Switzerland/S. Karger AG, Basel
Introduction
Early childhood is an important period for the development of health. Recent researches using different approaches (experimental or epidemiological) have shown the importance of this early period for metabolic programming [1]. This general concept of the “Developmental Origin of Health and Disease” (DOHAD) has been refined in humans to highlight the importance of the first 1,000 days for the development of health status [2]. In this context, our specific focus is on understanding how eating behavior is programmed during this period of the first 1,000 days. As a first observation, eating behavior undergoes a strong development during this period, in particular because the mode of feeding drastically evolves from conception until the age of 2 years. This implies that the child has to learn “how” to eat but also “what” to eat, “how much food” to eat, and “in which context” meals take place. After birth, when orally exposed to foods, infants discover their intrinsic properties, with a variety of tastes, flavors, textures, as well as energy densities, and all these aspects become even more salient at the onset of complementary feeding. By the end of the second year, food neophobia, i.e., the refusal of new food, develops [3–5]. We have previously observed that eating behavior established at the end of this period tracks on later into childhood and up to early adulthood [6–9]. Altogether, this calls for a better understanding of the driving factors and the key periods for the establishment of eating behavior during the first 2 years of postnatal life.
Here, we report several works in which we focused on deciphering the involvement of taste and olfaction in the early establishment of eating behavior over the first 2 years of postnatal life. We focused on both senses because they both strongly relate to the oral phase of feeding and because the chemosensory environment evolves strongly during this early period of life [10, 11]. In the frame of the OPALINE French birth cohort (Observatory of Food Preferences in Infants and Children), taste and flavor preferences were studied independently in children, as well as food acceptance and food neophobia over the course of the first 2 years of life.
Evolution of Taste and Odor Preferences in Early Life
At birth, previous works revealed evidence of differential preferences across tastes, with a preference for sweet taste, a rejection of bitter taste [12], and very little evidence of inborn flavor preferences (but rather of avoidance of smell of rotten foods [13]), except when infants had been previously exposed to specific flavors from the maternal diet [10, 11]. Thus, inborn taste and flavor preferences are not numerous although marked food preferences exist in adults and even in young children. It is then much needed to understand the factors contributing to the building of food preferences. The evolution of taste and flavor preferences at later stages in early childhood has received little attention. Within the OPALINE cohort, we studied longitudinally in a group of 285 infants the evolution of taste preferences from 3 to 20 months [14, 15] and the evolution of flavor preferences from 8 to 22 months [16].
Acceptance of each taste (sweet, salty, bitter, sour, and umami) and of a fat emulsion relative to water was defined based on ingestion or liking at 3, 6, 12, and 20 months of age [14, 15]. For each taste, 4 bottles were presented (water, tastant, tastant, water). The acceptance of each taste relative to water was defined using proportional variables that are ratios of ingestion or liking evaluated by the experimenter. These data were analyzed with mixed models that accounted for age and subject effects. Taste acceptance trajectories for all primary tastes and for a fat emulsion were modeled. For saltiness, acceptance increased sharply between the ages of 3 and 12 months. The trajectories of acceptance were parallel for sweetness, sourness, and the umami taste between 3 and 20 months, with sweetness being preferred. Between 12 and 20 months, the acceptance of all tastes, except bitterness, decreased, and at 20 months, only sweetness was not rejected. The acceptance of bitterness remained stable. For the fat emulsion, acceptance evolved from indifference to rejection. Moreover, more rejections were reported based on the judgment of the experimenter than of the infant’s liking. Ingestion and liking ratios are rather complementary, and this result highlights that a grimace is not necessarily associated with reduced ingestion.
Similarly, acceptance of each food odor was defined using proportional variables based on behavioral analysis [16]. Four control stimuli and 8 odors (4 rated by adults as a priori pleasant and 4 as a priori unpleasant) were presented in bottles to infants at 8, 12, and 22 months of age. The infant’s exploratory behavior towards odorized and control bottles was measured in terms of mouthing defined as a direct contact with perioral and/or perinasal areas. For each odorized bottle, durations of mouthing were calculated relative to the control bottles. In this age range, shorter durations of mouthing were found for unpleasantly scented bottles (trimethylamine, dimethyl disulfide, and butyric acid) than pleasantly scented bottles. So, between 8 and 22 months, unpleasant food odors lead to avoidance behavior in infants, but pleasant food odors did not elicit specific behaviors.
In these studies, we noted that developmental changes were dependent on taste and odor. We will now examine to which extent these developmental changes also depend on the taste and flavor experiences the infant receives during this period.
Effect of Early Taste and Flavor Experiences on Taste and Food Preferences
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
