Shaping dietary preferences


OBJECTIF NUTRITION 90 (DECEMBER 2008)
Dr Vincent Boggio
Dijon University Hospital Centre (CHU)
Sophie Nicklaus
The French National Institute for Agricultural Research (INRA) Dijon, Flavic Joint Research Unit (UMR)
Sylvie Issanchou
INRA Dijon, Flavic UMR



For the last fifty or so years, the increased availability of food and a certain relaxation in parenting have resulted in preferences being a determining factor in food consumption for many children. Asking a child to “change his dietary habits” is therefore tantamount to asking him to “set aside” his preferences. Knowledge of the shaping of dietary preferences is therefore useful to he who advises a child to change his habits. We soon realise that, whilst it is possible to influence dietary preferences, this is the case before they are acquired.

FOCUS

Dietary habits result from context (where, when and how do we eat?) and consumption behaviours (what do we eat? how much of it do we eat?). In adults, they are dependent on availability and dietary preferences. In children, these factors only influence consumption if they are taken into account by parents.

In children of hypermodern times, who have relaxed upbringings and are faced with the wide availability of food, preferences have become a determining factor in food consumption. Asking a child to “change his dietary habits” is therefore tantamount to asking him to “set aside” his preferences.

It is often said that we must “change our dietary habits”. The juxtaposition of these two contradictory terms, “change” and “habits”, highlights the difficulty of the undertaking from the outset. It is confronted, particularly during childhood, with the existence of dietary preferences. It would therefore seem useful to know how these are shaped.

FROM PREGNANCY TO DIVERSIFICATION

The shaping of dietary preferences begins in utero. Some odorous molecules pass into the amniotic fluid and sensory abilities can be seen from birth. Newborns lean towards certain odorous molecules consumed by their mothers in the latter stages of pregnancy. If they are breastfed, they prefer the smell of their mother’s milk to another breast milk. Newborns are also capable of making use of gestures and facial expressions to show their perception of flavours: sweetness provokes an expression of pleasure, bitterness and sourness displeasure, and saltiness variable reactions.

When children grow up, sweet flavours remain popular, bitter flavours continue to be rejected, and sour flavours gain favour with some children. The appeal of salty flavours increases and becomes marked at the age of two years with the notable exception of salted water.

It is difficult to study olfactory reactions and the impact of olfactory sensitivity on dietary preferences in infants and small children. Knowledge of the development of oral and nasal chemesthetic sensations (irritant, effervescent, astringent) and their impact on dietary preferences is still in its embryonic stage. Changes in the assessment of textures are, on the other hand, well known. They are linked to the development of the masticatory system: textures that are difficult to “manipulate” with the mouth are rejected. Preferences move progressively from soft to hard textures, whilst contrasting textures in the same dish remain unpopular with children.

The development of early preferences is dependent on the repetition of exposure: the innate attraction of infants for sweetness is strengthened by repeated exposure to bottles of sweetened water; children fed with hypoallergenic milk subsequently prefer its smell and taste. Adults who were given vanilla-flavoured milk as infants prefer the vanilla-flavoured version of ketchup!

The most surprising exposures are linked to breastfeeding as breast milk carries the odorous molecules of the foods consumed by mothers and its sensory qualities vary from day to day, and even from the beginning to the end of the feed (whereas the sensory characteristics of industrial milk are constant). Thus, when cereals prepared with carrot juice are offered to a child aged 5–6 months, he eats more if his mother consumed such juice during the first two months of breastfeeding! This is why the variety of aromatic experiences in breast milk is thought to predispose children to accept new flavours more easily during dietary diversification. How diversification is undertaken is an issue for the subsequent acceptance of foods, particularly those that children are the most reluctant to accept, such as vegetables. Alternating vegetables at the start of diversification, rather than repeatedly offering the same one everyday, encourages the subsequent acceptance of a new vegetable.

SHAPING HABITS FROM 3 TO 6 YEARS

Around the age of three years food neophobia becomes apparent. The acceptance of new foods then falls sharply. Furthermore, certain foods that were previously enjoyed may be rejected. Some children become much fussier than others. Taking neophobia into account should logically lead to children’s dietary repertoire being developed before the age of three years, meaning regularly offering them what will be available subsequently.

After the age of three years, all is not lost! Yet the acceptability of new foods is more difficult. It is promoted by the number of exposures, on the condition that such exposures involve tasting (the child must try the food) and are not purely visual.

The decisive influence of parents is revealed by the selection of foods that they make available to the child. Children consume more vegetables when there are more vegetables at home! A child is more likely to try a food if an adult eats some before he does, especially if the adult is a relative and consumes the food with pleasure.

Attempts by parents to control the types and amounts of food consumed generally prove to be counterproductive. The restriction of a food that is enjoyed increases the preference therefor and consumption thereof after the restriction has been lifted. Conversely, forcing a child to eat encourages the development of an aversion to the food, which remains pronounced for some time.

…AND AT SCHOOL AGE

From infant school, peer influence is established. A child’s preference for a food can be changed by having him eat with a peer whose preference for the food is different. It may be a simple effect of imitation or of social conformity: the child is thought to be seeking to be better accepted or less rejected. However, this effect is fleeting. During adolescence, the growing role of peers is often stressed. It is limited to snacks, but community identity may occasionally be expressed by highly distinctive dietary habits.

THE GAFFAREL STUDY (DIJON, FRANCE): 1982–2002

Dietary choices of two- to three-year-olds

From 1982 to 1999, two- to three-year-olds at the Gaffarel crèche in Dijon, France, were offered a menu of eight foods: two starters, meat/eggs/fish, two accompaniments (generally one vegetable and one starchy food), two cheeses and bread. The children were free to put together their meal whilst respecting the following rules: "I take my plate with me, I serve myself, I pick what I want, I can take several things, I go back to my seat, I eat everything that I have chosen before taking another helping, I do not take the same thing more than three times". The childcare assistants noted the children’s choices. On average, each of the 418 children was observed at 109 (±48) meals during which 117 (±19) different foods were on offer.

The most commonly chosen foods were animal products, starchy foods and pre-cooked meals. The children tended to prefer high-calorie foods. Hot dishes were chosen more often than their cold equivalents. Mixed foods were seldom chosen. The avoidance of certain foods appeared to be linked to their sensory proprieties: strong aromas, sourness, bitterness, and fibrous texture. The cheeses were chosen less frequently than meat or starchy foods despite similar calorific values, probably due to their sensory characteristics (notably for mature cheese). Individual differences in selection, which were very great, were not explained by sex, corpulence, initial method of feeding, older/younger siblings or the socio-professional category of parents. An attempt to categorise the children according to their profiles (carnivores? vegetarians?) failed, except for one particular segment (7% of the children): those who systematically avoided the cheeses.


Dietary choices at the age of two–three years and subsequent preferences

In 2001 and 2002, 341 former attendees of the crèche, aged from 4 to 22 years, were questioned at the INRA in Dijon and the European Centre for Taste and Smell on their current preferences for foods that had been offered to them at the crèche, the variety of their diet, and their degree of food neophobia. Statistical modelling studied if their current dietary preferences were linked to their choices at the age of 2–3 years, age, sex, corpulence, duration of feeding that they received and the socio-professional category of their parents.
 
Conclusion: choices at the age of 2–3 years are the strongest contributing variable to predicting current preferences. The stability of preferences is particularly marked for animal products, cheeses and starchy foods until the age of 17–22 years and for vegetables until the age of 13–16 years but only in girls. The order of preferences remained stable for a large number of flavoursome foods. Studied food by food, concordance between choices at the crèche and current preferences is found again for all mature cheeses and 50% of other foods: most have distinct flavours.

Preferences for vegetables and pre-cooked meals increased with age but fell for cheeses, starchy foods and, in girls only, animal products. Corpulence has an effect on current preferences for animal products only, which are less popular amongst more corpulent girls. They are not dependent on the duration of breastfeeding or the profession of the parents.


Variety at the age of two–three years and subsequent variety

Children who showed greater variation in their choices at the crèche currently have a broader dietary repertoire. Variety also increases when the neophobia score is lower, when the children are older (17–22 years rather than 4–7 years), and when they were breastfed for longer. The link between the variety at the age of 2–3 years and subsequent variety is particularly strong for vegetables and dairy products. Increased variety of animal products with age is only observed in boys. Corpulence and profession of the parents have no influence. Boys who chose a wider variety of foods at the crèche subsequently consumed more unfamiliar foods. Yet at a tasting session new foods were not more popular amongst those whose choices at the age of 2–3 years were more varied.
 
Nicklaus S, Boggio V & Issanchou S. Food choice at lunch during the third year of life : high selection of animal and starchy foods but avoidance of vegetables. Acta Paediatrica, 2005; 94: 943-51.
Nicklaus S, Boggio V, Chabanet C & Issanchou S 2004. A prospective study of food preferences in childhood. Food Quality and Preference, 2004, 15, 805-18.


CONCLUSION

It appears therefore that the shaping of dietary preferences is firstly linked to the sensory aspects of foods, and is then honed by the environment (exposure to foods, upbringing). We would like it to be influenced by knowledge of the nutritional qualities of foods too. Such knowledge is limited in young children and not incorporated into their thought process before the age of 10–12 years. By them, the notion “healthy” is interpreted as “tasty”.

For the majority of children, information on the pleasant taste of a new food increases the frequency of consumption thereof whereas nutritional information has no effect. However much nutritional education campaigns further nutritional knowledge, they do not alter consumption.

Although it does not, in the short term, change their dietary preferences, the nutritional knowledge gained by children may be useful to them when they are parents and wish to instil “good dietary habits” in their children. Yet scientific knowledge is advancing and current nutritional recommendations may no longer be relevant in 25 years!