Aceite de oliva y aceituna de mesa

On the basis of the research in this thesis, there are general reflections relating to children’s fruit and vegetable consumption that should be considered. In line with Figure 1.1 in the Introduction, we now discuss factors relating to the product, person and environment.

Product-related factors

A basic assumption in this thesis is that children’s fruit and vegetable intake can be encouraged by increasing children’s preferences. But a preference for a specific food is not sufficient to guarantee consumption ^{(69, 70)}. Although children like fruit

(49, 64, 71, 72), their intake is still insufficient. A dislike may be a more important driver of behaviour ⁽⁷³⁾, in that children refuse to eat disliked foods. This is obvious for vegetables; children’s dislike hinders their vegetable consumption. This implies that increasing children’s preferences is a more important strategy for vegetables than for fruit. In addition, a product-approach that changes vegetable characteristics (taste, texture) is more relevant for vegetables than for fruit.

Both these points support the notion that fruit and vegetables should be treated separately and need different intervention strategies (see Chapter 3).

What is then needed for vegetables? The bitter taste of vegetables, the low energy content and textures that are difficult to control are not attractive characteristics for children (49, 74-77). Strategies that reduce these characteristics would be most promising. However, due to children’s dislike for vegetables, vegetable research among children is not easy; voluntary child participation may be challenging, drop-out during the study may be high ⁽⁷⁸⁾ and it may be difficult to investigate effects of specific strategies when sufficient vegetable consumption is required. Research should focus on moderately consumed and moderately liked vegetables as these are most changeable ⁽⁷⁹⁾. Adding liked and familiar toppings or sauces to vegetables ^{(78, 80)}, serving vegetables raw or as crunchy as possible

(49, 81-83) and using spices to mask the bitter taste are fruitful ways to continue.

Our flavour-nutrient learning study (Chapter 6) indicates that intense vegetable flavours should not be used.

A fundamental issue is the vegetable intake recommendations for children.

Child recommendations vary between countries or there are no specific recommendations for children ⁽⁸⁴⁾. When there are child recommendations, they are deduced from the WHO adult recommendations. Since hardly any child worldwide reaches the recommended vegetable intake (27, 33, 40, 84-86), one could ask the question: Are these vegetable recommendations for children realistic and valid? In our choice-offering study (Chapter 7), the children consumed on

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General discussion

average 50 grams of vegetables, whereas 100-150 grams is recommended. Only 22% of the children ate more than 100 grams, and the children in this study came from relatively highly educated families. Although it is likely that children ate less due to the research setting, it is unlikely that their habitual intake would be double or triple. Therefore, more research about the ‘right’ recommendations per age group is required, as well as harmonization of the child recommendations worldwide.

One might also speculate that, if vegetables are so healthy for children, would there not be a biological principle supporting this? Although it is appealing to believe in ‘the wisdom of the body’, this wisdom has never been proved ⁽⁸⁷⁾. Whereas flavour-nutrient learning, neophobia, an inborn dislike for bitter tastes and a high taste sensitivity to bitterness were valuable in prehistoric times, they are not supportive of vegetable intake. In a world where safe food is in abundance, consuming vegetables may be helpful with regard to the obesity epidemic ^(88,

89). In addition, food habits and preferences acquired at a young age track into adulthood ^(90-92). So, eating plenty of vegetables as a child increases the probability of sufficient consumption in adulthood.

Person-related factors

We took cognitive development into account as a new perspective for studying children’s fruit and vegetable behaviour. Our qualitative study (Chapter 2) indicated that the link between healthy and distaste (49, 93-95) is not yet present in 4-5-year-old children. It seems that, at a certain age, this association alters, and we hypothesize that vegetables play an important role in this switch. Parents may tell their children that they should eat their vegetables because vegetables are healthy ⁽⁴⁹⁾, but, in the long term, this could result in a link between healthy and not tasty. Since pre-operational children are not yet able to make deeper and long-lasting associations (2, 8, 96, 97) and they do not yet understand the full concept of health (Chapter 2), it seems plausible that such a link emerges in the concrete operational stage, starting from the age of 7 years. Research is needed to confirm this hypothesis.

Another interesting topic concerning children’s cognitive development is their perception of quantities. Children’s perception of a particular quantity may depend on the shape in which it is presented ^{(2, 96)}. This developmental difference concerning perceptions of quantity was also present in our qualitative study and the choice-offering study. It seems therefore promising to present vegetable portions in such a way that children perceive these portions as doable instead of huge.

Besides cognitive developmental differences between age groups, there are also age-related differences concerning physical development. Developments concerning jaws, teeth and surrounding muscles ⁽⁷⁷⁾ can influence which textures

Chapter 8

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are accepted or rejected. Developments concerning hand locomotion influence preparation skills and determine which fruit and vegetable products can become accessible to the child ⁽⁹⁸⁾. In addition, there are age-related differences in the intensity of certain trait characteristics, such as neophobia, which peaks between 2 and 5 years ^(99-101), and reactance ^(102-104). These differences may run parallel with cognitive development and can influence fruit and vegetable eating experiences

(105-108). Therefore, we suggest more research into these age-related differences

in order to make healthy eating interventions as relevant and meaningful as possible for children.

The research in this thesis focused on primary school-aged children. Is this the right age to increase children’s vegetable preferences? Because food preferences and nutritional habits are relatively stable from early ages on ^(90-92), one could suggest starting earlier. Early exposure, such as via breastfeeding, positively influences vegetable acceptance ^(109-111), and there may be a sensitive period for learning in the first two years ^{(99, 100)}. Repeated exposure to vegetables in infants leads to large increases in intake ^{(109, 111)}. So, starting at a younger age would certainly be beneficial. On the other hand, we continue to learn to accept new foods beyond childhood (coffee, beer, olives etc), indicating that preference learning mechanisms are still present. In adults also, vegetable preferences can be increased by flavour-flavour learning ⁽¹¹²⁾. Thus, although more effort may be needed when children become older, it is never too late to change food preferences.

Environmental factors

Although it is known that parents play an important role, the majority of fruit and vegetable intervention programmes are school-based with little parental involvement. Many parents are eager to encourage healthy eating in their children

(113, 114), and are open for specific and concrete information that can help them. On the other hand, more and more parents are both employed outside the home and consequently have less time to take the action that may be needed. Parents search for convenient and flexible ways to serve their children healthy meals, while maintaining a pleasant meal situation. In addition, children themselves indicate the importance of parental support as a facilitator for healthy eating ^{(115, 116)}.

The use of parental strategies is a complex area. Most research about parental practices is cross-sectional, making it impossible to elucidate cause and effect

(117-120). Parents often use a mixture of practices ^(52-54), and these practices are shaped via an interactional relationship: parents apply practices to influence their children’s eating behaviour, but parental practices also develop in response to the children’s behaviour (57, 120-122). In addition, often subtle mechanisms are involved, with certain practices showing positive as well as negative effects on

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children’s eating (26, 56, 86, 123-125). Whereas one would like to be able to confirm the effectiveness of one single practice that could easily be recommended, this may not always be a reflection of reality. Moreover, the literature about parental practices and strategies uses a variety of terms and concepts ⁽¹²⁰⁾. Thus, a deeper understanding of these concepts is needed together with more uniformity regarding the terms.