The early flavor experience of formula-fed infants is markedly different from that of breastfed infants. Exclusively formula-fed children do not benefit from the ever-changing flavor profile of breast milk. Their flavor experience is more monotone and lacks the flavors of the foods of the mother’s diet. There are striking differences in flavors among the different types and brands of formulas, and formula-fed infants learn to prefer the flavors of the formula they are fed and foods containing these flavors [20]. This is indicated by a study on a milk substitute containing hydrolyzed proteins (hypoallergenic nutrition). This milk substitute for infants with a severe milk protein allergy has an unmistakably sour and bitter “burnt” taste. Infants who were fed this milk substitute for the first time at the age of 2 or 3 months accepted it even at the age of 7 months. However, if infants were offered this milk for the first time when they were 6 or 7 months old, they rejected it entirely [25]. Moreover, infants who were fed hydrolyzed baby milk for several months at a very early age were more willing to accept sour-tasting beverages when they were 4 or 5 years old [26].
A Spoon of Variety at Complementary Feeding – A Window of Opportunity
The complementary feeding period is a “window of opportunity” for acclimatizing infants to the taste of a wide variety of foods. Early learning about flavors continues during the complementary feeding period through the introduction of solids and changing exposures to a variety of new foods. In this particular time of the child’s life, there is the transition from breastfeeding/formula feeding to a complementary solid diet, and infants discover the sensory (taste, flavor, and texture) and nutritional properties (energy density) of the foods that will ultimately compose their adult diet [27]. Infant acceptance of new tastes and flavors develops during the so-called “sensitive period” between 4 and 6 months [28]. This period is crucial in influencing the development of later food preferences. The period from 6 to 10 months is favorable for the introduction of more complex textures [28]. The early and easy acceptance of new foods at a slightly younger age in the period of the introduction of complementary foods (4–6 months) has been observed in many studies. It has been shown that the earlier fruits and vegetables were introduced, the better their acceptance both in infancy and at a later age in childhood. This possibly reflects the difficult nature in terms of texture and tastes shared by many fruits and vegetables, both properties which children find aversive. The only texture the infant has experienced before complementary feeding is thin, liquid, warm milk, and thus new textures like soft-cooked vegetables and even thick yogurt will feel wildly different. The oral motor skills are usually learnt between 6 and 12 months of age (the period in which the tongue learns to move solid food around the mouth in preparation for swallowing), and this ability is dependent upon the experience of textured food within the mouth rather than on any particular age or developmental stage [28]. It has been observed that if 12-month-old infants were given pureed and chopped carrots, they consumed more of the pureed carrots, but there was variability in the infants’ willingness to take the chopped carrots. The strongest predictor of the acceptance of chopped carrots at 12 months – other than the presence of teeth – was earlier experience with textured foods [29]. In addition, children who were used to a high variety of different foods in their diet ate more of the chopped carrots; this again reflects the generalization effect, the greater the experience, the greater the willingness to try. Furthermore, infants who are introduced earlier to lumpy foods tend to be easier to feed by their mothers than children introduced to lumpy solids after the age of 10 months. Children introduced to lumpy solids after the age of 10 months were reported as having more feeding problems at 7 years. They were also reported as eating fewer portions of fruits and vegetables at 7 years [30].
At the onset of complementary feeding, many infants dislike vegetables, and there are various reasons for this, including the taste, appearance, and texture, often influenced by how they are prepared. Being exposed to a variety of foods during the complementary feeding period helps modulate the acceptance of new foods, especially vegetables, in the first year of life and later on [1, 10, 11]. It has been shown that experience with a variety of vegetables (changing the vegetable offered each day) at the very onset of weaning increased intake of new foods a few weeks later [10] but also a few years later [1]. Breastfeeding and early experience with variety interacted, in that infants who had been breastfed and had then experienced a high variety of vegetables at weaning showed the most marked acceptance of new foods [10]. In a follow-up study, it has been shown that the benefit of introducing a variety of vegetables maintains at least up to the age of 6 years [1]. At 6 years, children who had been exposed to a high level of variety consumed more of the new and known vegetables, were more willing to taste vegetables, and had higher liking scores for new or familiar vegetables [1].
At present, the first weaning food in many European countries (e.g., Germany), such as vegetables, potatoes, and meat, is thus increasingly competing with the variety and, following the Mediterranean model, also fatty sea fish. The long-held view that only 1 or 2 vegetables per week should be fed has become obsolete. Monotonous nutrition offers no protection against allergies and better food intake. On the contrary, infants who receive a varied complementary diet are also better and less complicated eaters later in life. Parents should, therefore, pay attention to a variety of fruits and vegetables at the beginning of the complementary feeding. Offering the infant a variety of flavors and textures from the start of complementary feeding is the best way to help them to enjoy a variety of foods as they grow up.
In conclusion, a preference for varied flavors should ultimately increase the range of nutrients consumed and the likelihood that a well-balanced diet is achieved. In other words, the variety effect may reflect an important adaptive mechanism in the regulation of food intake among omnivores.
Repeated Exposure
Despite the new freedom to introduce a variety of foods, many infants and young children are still unable to find the optimal nutritional mix. Vegetables may be rejected for a number of different reasons, from their bitter taste, unfamiliar texture, their relatively low energy content to simple lack of access in many families. Infants are born with about 10,000 taste buds and are, so to speak, real supertasters at birth. Although they have a genetic preference for sweets, they also have an aversion to bitterness. Whether fennel, broccoli, or artichoke – even the smallest trace of bitter substances often does not escape the highly sensitive child’s palate. Thus, the following question emerges: Can children learn to like vegetables? What the infant tastes or does not taste is a question of training. Many parents give up here too soon. So, what to do when gourmet babies stubbornly resist something new? The most successful strategy to promote vegetable intake is repeated exposure [1, 12–14]. Repeated exposure to the pure/distinct taste of a vegetable during complementary
