Christiaan Hamaker Prize – Winning Thesis: Optimal Defaults and Children’s Nutritional Choices

The Effect of Optimal Defaults on Children’s Nutritional Choices

Shriya Bang

University of Amsterdam

The obesity epidemic continues to pose significant challenges, demanding innovative and effective solutions. To this end, nudges are known for their gentle yet powerful effect across various health domains. This literature review investigated the effect of optimal defaults on children’s nutritional choices. The hypothesis was that optimal defaults positively affect children’s nutritional choices, that is, when the optimal, nutritional choice is set as the default, it will be chosen more often than a suboptimal, less nutritional alternative. This effect was consistently found through a comprehensive analysis of relevant studies with diverse settings and samples. Hence the application of optimal defaults emerges as a promising intervention strategy to encourage nutritional choices in children.

The Effect of Optimal Defaults on Children’s Nutritional Choices

Childhood obesity is a growing problem, and poor nutrition is a major contributing factor (World Health Organisation, 2021). Children are eating out more frequently, and most of these commercial meals are unhealthy (Adams et al., 2015). Hence, in dealing with childhood obesity, optimal nutrition should be targeted at the level of eating outside at food establishments. For this review, a nutritional choice is defined by relative energy density, which is the number of calories (kcal/g) in a particular food, according to the Harvard School of Public Health, with lower-energy-dense foods tending to be healthier than higher-energy-dense foods (Food and Diet, 2016). Optimal nutrition through restrictive policies is specifically dysfunctional for children, because children are specifically prone to reactance in response to restriction (Jalonick, 2014). The alternative is gentle nudging. 

Nudges are environmental changes that affect behaviour without limiting choice (Thaler & Sunstein, 2008). Previous research shows that various nudges positively affect children’s nutritional choices (Lycett et al., 2017; Hanks et al., 2012). One such nudging strategy is optimal default choice, which has robust positive effects on health domains like organ donation (Abadie & Gay, 2006), medication (Ansher et al., 2014) and vaccination (Chapman et al., 2010). Since children’s nutrition is also a health domain, it makes sense to investigate if optimal defaults, a prominent nudge, hold promise in influencing nutritional choice, as they do in other health domains. An optimal default is a pre-selected option that promotes a favourable outcome while preserving one’s ability to opt-out of the default and choose an alternative (Thaler & Sunstein, 2008). In this review, this definition is applied to nutritional choices, with a pre-selected optimal default referring to a lower-energy-dense food.

The previous findings can be explained by the default effect in nudge theory (Thaler & Sunstein, 2008). It suggests that decision-makers, in this case children, are generally not rational. Given different food options, a rational decision-maker would evaluate all choices in a balanced way, considering all factors like nutrition and taste. They would not be influenced by any food being the default. However, decision-makers consider choice to be a nuisance. When presented with a default food, they tend to accept it because the default choice, nutritious or not, is the easiest and most convenient option to choose. Changing the default, for instance by actively requesting the server, creates a ‘transaction barrier’, imposing a cognitive cost by requiring mental effort, even if the alternatives are well understood or preferable. Children in this case tend to be ‘cognitive misers’ and save mental energy. Therefore, if a nutritional food is set as the optimal default, they would choose it more often than a cognitively costlier, less nutritional alternative. According to Richard Thaler (Thaler & Sunstein, 2008), Nobel Prize Winner and the pioneer of nudging, “If you want to encourage some activity, make it easy” (p. 56).

In summary, previous research has established that many nudges positively affect children’s nutrition, and optimal default choice is a nudge that positively affects many health choices. This is based on the default effect in nudge theory. A nutritious default creates a cognitive cost for choosing the suboptimal alternative. Since people tend to avoid cognitive costs, they often choose nutritional defaults. However, it is not yet known if optimal defaults can create this cognitive cost in children’s nutritional choices. Hence, this literature review will investigate whether optimal defaults affect children’s nutritional choices. The hypothesis is that when the optimal, nutritional choice is set as the default, it will be chosen more often than a suboptimal non-default alternative, hence optimal defaults will positively affect children’s nutritional choices by making the suboptimal choice cognitively costlier than the nutritious one, harnessing the mind’s tendency to avoid this cost.

To address the research question, this literature review will start out by describing a laboratory experiment that studied that effect of default choice on children’s nutritional decisions. Then, this effect will be investigated in a real-life restaurant setting in a field study, to see if the findings replicate. Then, a study will test this effect on a sample of children at risk of developing obesity, and the final experiment will see if the finding generalises when parents were involved in the children’s choices. Hence, by considering these four cases, it will become clear if optimal defaults affect children’s nutritional choices.

Empirical Evidence

Ferrante et al. (2022) studied the effect of optimal defaults in children’s side dish menu orders in a laboratory setting in 48 children, 25 boys and 23 girls, aged four to eight. Participants were randomly assigned to two conditions. In the optimal default condition, the default side dish on the menu was a plate of low-energy-dense carrots (150g). Children could opt out and request an alternate plate of higher-energy-dense fries (150g). In the suboptimal default condition, the default side dish on the menu was a plate of fries (100g) and carrots (50g). Children could opt out this plate and request an alternate plate of all fries (150g) or a plate of all carrots (150g). To measure nutritional choice, researchers counted the number of orders of both optimal carrots and suboptimal fries in each condition. Results showed children in both the optimal and suboptimal default condition ordered the default side dish more often than the alternate side dish. Children in the optimal default condition ordered carrots (the optimal choice) more often than children in the suboptimal default condition. Researchers concluded that optimal defaults positively affect children’s nutritional menu-ordering behaviour. 

However, this study was conducted in a highly controlled artificial laboratory setting; hence the findings have low ecological validity, that is, the degree to which findings are representative of conditions in the wider world (American Psychological Association, n.d.). This is relevant because the findings may not fully reflect real-life settings in which children generally make nutritional choices. For example, participants did not pay for their meal – a situation that is not reflective of mundane realism. To address this, the next study is a field experiment, conducted in a real restaurant and sampling real diners. Looking at both a well-controlled setting and more ecologically valid setting provides a comprehensive understanding of the issue, leveraging the benefits of both. 

Dalrymple et al. (2020) studied the effect of optimal defaults in kids’ menus at a theme park restaurant in 1704 children. Since this was a field experiment, the restaurant’s standard operating procedures were followed and data about the age and gender of participants was not collected. All items in the restaurant’s menu were divided into lower or higher energy density (for example, milk or soda, respectively). Then participants were randomly assigned to three conditions. In the optimal default condition, the lower-energy-dense items were set as default. In the suboptimal default condition, the higher-energy-dense items were set as default. In both the optimal and suboptimal default condition, the default items were served unless participants requested the server for the alternative. In the free choice condition, there were no defaults and participants could pick any item. Nutritional choice was measured by counting the number of times lower-energy-dense items were selected in each condition. Results showed that lower-energy-dense items were selected more often in the optimal default condition, compared to both the suboptimal default and the free choice condition. Researchers concluded that optimal defaults positively affect children’s nutritional choices in a real-life restaurant. 

This study was conducted with a sample of physically healthy children. However, since nutritional defaults are relevant for targeting child obesity, it makes sense to test if the findings generalise to a population at risk for obesity. This is relevant because an at-risk sample may differ in their nutritional choices, possibly due to different nutritional needs and unique challenges faced by them. For example, they may have a higher preference for unhealthy foods, which could affect their receptiveness to default nudges. To address this, the next study used a sample of children who were identified as ‘low vegetable consumers’ (less than two servings per day) as well as who were at genetic risk for obesity based on family history. This way, the specific factors that impact the nutritional decisions of these children can be accounted for.

Cravener et al. (2015) studied the effect of presenting vegetables as the default snack at home in 24 children, 12 girls and 12 boys, aged three to five, who were ‘low vegetable consumers’ and at genetic risk for obesity. During the pre-intervention week one (baseline), parents presented a free choice between vegetables and chocolate granola bars, with vegetables being lower-energy-dense and more nutritional than chocolate granola bars. During week two and three, the intervention was introduced. Participants were randomly assigned to two conditions. In the control condition, participants continued the free choice from week one. In the treatment condition, vegetables were presented as defaults. Children could opt-out by actively requesting the chocolate granola bar. During week four (follow-up) the treatment was removed again, and it was a repeat of week one, with a free choice presented again. Researchers wanted to see if the treatment effects would reverse back when the treatment is removed, so that causality can be established even more strongly. Nutritional choice was measured by the amount of vegetable intake in grams. Results showed that participants in the treatment condition increased vegetable intake from week one (baseline) to two, relative to the control condition. This effect was not sustained at week four when the treatment was removed, suggesting that the optimal default was indeed responsible for the positive effect on nutritional choice. Researchers concluded that optimal defaults positively affect nutritional choices in children who are vulnerable to obesity. 

However, parents who presented the food items here were asked to be extremely neutral, as a control for the experiment. They were asked not to engage in parental feeding tactics like pressuring or coercing children, bribery or punishment. However, in mundane realism, parents do have some involvement in children’s nutritional choices, which may impact the choice made if the child gets influenced, for instance if parents scold children for unhealthy choices, then children are more likely to choose a healthier option, to avoid such punishment. Hence, parents are important to consider. The next study will address this by having a sample of parent-child dyads so that parents are at least minimally involved in the choice. But to keep focus on the research question at hand, the main ‘nutritional choice’ of whether to consume the selected food will still rest on the child. 

Loeb et al. (2017) studied the effect of optimal defaults on breakfast choices in 62 parent-child dyads with children aged three to eight, 35 boys and 27 girls, in a community dining room setting. The dyads were randomly assigned to two conditions. In the optimal default condition, the default breakfast menu had lower-energy-dense items (like bananas). In the suboptimal default condition, the default breakfast menu had higher-energy-dense items (like Kool-Aid). In each condition, default items were prominently displayed on the menu and the alternate breakfast was listed at the bottom as ‘available upon request’. The default breakfast of each condition was served to them respectively if no request for an alternative had been made. Nutritional choice was measured by waste plate methodology, which measures the quantity of food that is consumed. Results showed children in both the optimal and suboptimal default condition selected the default breakfast menu more often than the alternate menu. Children in the optimal default condition consumed a greater quantity of lower-energy-dense breakfast than children in the suboptimal default condition. Researchers concluded that optimal defaults positively affected nutritional choices in parent-child dyads.

Conclusions and Discussion

The present literature review investigated the effect of optimal defaults on children’s nutritional choices. The main conclusion is that optimal defaults positively affect children’s nutritional choices, based on four studies reviewed which found that when the optimal, nutritional choice is set as the default, it will be chosen more often than a suboptimal non-default alternative. This effect emerges both in a laboratory and a real-life natural setting, in both normative and at-risk children, and even with parental involvement in the choice. This is consistent with what was expected, as it aligns with the main hypothesis which predicted a positive effect of optimal defaults on children’s nutritional choices, in that, when the optimal, nutritional choice is set as the default, it will be chosen more often than a suboptimal non-default alternative. This finding is in line with the default effect in nudge theory (Thaler & Sunstein, 2008), which explains this finding by suggesting that nutritious optimal defaults create a cognitive cost for choosing an unhealthy alternative, and because people tend to avoid cognitive costs and save mental energy, they often go with the optimal default choice. Hence when the default treatment is removed, and free choice is presented again, both nutritional and non-nutritional choices have the same cognitive cost, and the positive effect disappears, reinforcing the main finding that optimal defaults are responsible for increasing nutritional choice through their influence on the cognitive cost of choice. The main conclusion also aligns with previous research that indicated a potential positive effect of nudging techniques like defaults on health domains like nutritional choices. However, it should be noted that this finding can be alternatively explained, as default choices may act as an implicit recommendation. Children may lack expertise in nutrition and assume that the pre-selected option is set as such for a reason, and by someone with more expertise than them (McKenzie et al., 2006). So, they consider it advisory and hence accept it, instead of accepting it to save mental energy. 

It is essential to acknowledge certain limitations in this review. The operationalisation of nutritional choice should be considered. All studies define nutritional choice using energy density. While energy density is a widely used criterion, other factors like vitamin, protein and antioxidant content may also be relevant in defining whether a choice is nutritional. Energy density alone may not fully capture the complexity of nutrition. It is expected that considering additional aspects may reveal nutritional differences. For instance, tuna is low-energy-density but high in protein. Foods with similar energy density levels can have different protein content, for example, chicken and potatoes have similar energy densities but chicken has more protein. So, various aspects impact the overall nutritional value of any item. Hence, future research could benefit from incorporating more comprehensive measures of nutritional choices like vitamin or protein content. This would provide a more nuanced understanding of how optimal defaults affect children’s nutritional choices. 

Additionally, all studies primarily focused on examining the relatively short-term effects of optimal defaults on children’s nutritional choices, with intervention durations spanning less than a month. While these studies provide valuable insights into the immediate impact of optimal defaults, it remains unanswered if defaults can promote sustained habitual changes in nutrition. Establishing lasting behavioural change requires a longer timeframe, approximating three months in health-based behaviours like nutritional choice (Gardner et al., 2012). Future research could address this by incorporating follow-ups or adopting a longitudinal design, for instance training parents to present optimal defaults regularly over several months. This could assess if the effect found in the present review is enduring.  

Though results are encouraging, these limitations warrant caution when interpreting the findings. More importantly, they reveal opportunities for future research, which would lead to a more comprehensive exploration of the topic. Nonetheless, the evidence presented indicates that optimal defaults are compatible with the aims of public health policies that target child nutrition, health-based regulations for food establishments, and childhood obesity prevention. Overall, the gentle power of seemingly trivial optimal defaults can be harnessed to improve children’s nutrition.