The beneficial effects of eating fruit and vegetables are widely acknowledged [1,2]. However, many children do not meet the recommended guidelines for fruit and vegetable intake [3-5]. The Dutch recommendations for 4–12-year-old children of 150 grams of vegetables and two pieces (≈200 gram) of fruit, are in line with international guidelines [6]. Because food preferences and eating habits established in childhood often persist into adulthood, children are an appropriate group to target in order to positively influence dietary habits [7-9].
In recent years, several studies and programs have been set up to increase fruit and vegetable intake in children [10,11]. Positive changes have been found in knowledge, self-efficacy, skills, awareness, liking and intake. However, real, long-term successes have been difficult to establish [10,11]. To our knowledge, there is one recent study that did show long-term effects of a one-year free school fruit programme on children's fruit and vegetable consumption [12].
Preference is an important predictor of children's food intake [8,13-15]. For vegetables in particular, children's preference is low [15-18]. Therefore, to stimulate fruit and vegetable consumption among children, more should be known about their preferences, how these develop and how they can be influenced.
Most research about children's preferences does not take the possible role of children's cognitive development into account. Cognitive development represents "the sequence of changes that occur to the cognition of a person as they mature" [19]. Cognition refers to "the mental processes responsible for perception, attention, learning, memory, thought and communication" [20]. The aim of this study is to explore the relation between children's cognitive development and their perceptions of, and preferences for, fruit and vegetables.
Cognitive development and nutrition behaviour
Jean Piaget developed a cognitive development model with four successive stages: sensory motor period (0–2 years), pre-operational stage (2–7 years), concrete operational stage (7–11 years) and the formal operational stage (11–15 years). Along these stages, children's thinking changes from concrete to abstract, they develop the ability to replace overt actions by mental representations, egocentrism and centration diminishes, children develop more eye for detail, their information processing capacities increase, and their problem solving becomes more and more advanced [21-24].
For our study, we selected three age categories to study a broad range of cognitive development: 4–5-year-old, 7–8-year-old and 11–12-year-old children. Table 1 summarizes the cognitive developmental differences between the three age groups.
A few studies in the area of nutrition behaviour have taken cognitive development into account. Contento's [25] investigation about how children think about food and eating revealed that children in the pre-operational stage did not make a distinction between foods and snacks, whereas children in the concrete operational stage did. Pre-operational children believed that the ingested food went into the stomach and did not change in the body. Concrete operational children understood that food was changed somehow in the stomach. Pre-operational children could mention foods that were healthy, but they could not explain why. Concrete operational children could tell that food made you strong, healthy and made you grow, but they could not explain why or how this occurred.
Bahn [26] studied brand preferences and brand discriminations. Affectively based attributes, such as liking the taste or liking the colour of the package, were dominant in pre-operational and concrete operational children when they were distinguishing brands. Regarding preferences, concrete operational children focussed more on cognitively based attributes, such as healthiness and adultness, than pre-operational children.
It is interesting to note Rozin et al.'s perspective in this context. They showed that there is a gradual emergence of different categories of food rejections as the child matures [27,28]. Very young children of 1–21/2 years old accept almost all kind of edible and inedible substances. The first rejection category to appear is distaste; disliked products are rejected. Secondly, rejections based on danger appear. This means that products are rejected because negative consequences of ingestion are expected. The third rejection category is based on the idea of what something is or where it comes from (ideational). This category can be split into disgust, and inappropriateness. Disgust means that the association with the food product is averse, whereas inappropriateness means that the food product is not considered to be a food. It is not until the age of 7 that children differentiate between disgust and inappropriateness. The idea of contamination appears gradually between the ages of 31/2 years and 12 years. A food is contaminated when even a trace amount of a disgusting or inappropriate product has been or is present in the food [27,28]. This development of rejection is in line with the development of the child. Between the ages of 2 and 7, children become more independent eaters and they have to learn which foods are edible and which foods are not [21,28].
The nutrition studies above show that children in distinct cognitive stages think, decide and perceive food topics differently. The ideas children have about specific foods can influence their preferences, their willingness to taste and their whole eating experience [29]. Consequently, these different thoughts, perceptions and decision strategies may significantly impact on interventions aimed at changing food preferences and intake. Because most current approaches have not been effective in establishing long-term changes in fruit and vegetable consumption, cognitive development may be a promising field for achieving such changes; new approaches that are appropriate with regard to cognitive development will correspond closely with the children's natural development. In this study, we explored how the differences in cognitive development relate to children's perceptions of, and preferences for, fruit and vegetables. On the basis of the cognitive development theories, we expect that the number of cognitions about fruit and vegetables will increase as children grow up and that these cognitions will increase in complexity and abstraction.
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