Supersize me. Serving carrots whole versus diced influences children’s consumption
Introduction
An adequate consumption of vegetables aids in the prevention of obesity and chronic diseases such as certain forms of cancer and cardiovascular diseases (Wang et al., 2014). The Australian National Health and Medical and Research Council recommends that children consume at least 5 servings (i.e., 375 g) of vegetables a day (NHMRC, 2013), which is similar to what is recommended in the United States (USDA, 2015) and by the World Health Organization (WHO, 2017). However, less than 10% of Australian children aged 4–18 years of age actually meet the recommended daily consumption of vegetables (Australian Bureau of Statistics, 2013), with similar patterns reported in other countries (Darfour-Oduro et al., 2018, Vereecken et al., 2015).
There are a variety of reasons why children do not eat enough vegetables (Birch, 2007, Blanchette and Brug, 2005, Cooke, 2007, Knai et al., 2006). However, children’s rejection of the taste of vegetables has consistently been identified as a dominant barrier to higher intakes (Appleton et al., 2016, Brug et al., 2008, Poelman et al., 2017, Wadhera et al., 2015). Food liking (and in particular rejection/disliking) plays an instrumental role in children’s food choice and consumption (Cooke, 2007, Mennella et al., 2016, Mennella et al., 2016). Although children’s innate taste biases (e.g., rejection of bitter taste) affect initial liking of vegetables (Poelman, Delahunty, & de Graaf, 2015), these can be readily modified with repeated exposure (Anzman-Frasca et al., 2012, deWild et al., 2015, Hausner et al., 2012, Lakkakula et al., 2010, Reinaerts et al., 2007, Zeinstra et al., 2018, Rioux et al., 2018) especially in conjunction with positive consumption experiences such as eating vegetables in reinforcing social situations (Wardle et al., 2003, for review see Nekitsing, Blundell-Birtill, Cockroft, & Hetherington, 2018).
In addition, a change in the vegetable’s sensory profile can increase liking and consumption. In a number of studies Poelman and colleagues showed that preparation methods of vegetable (e.g., steaming, boiling, stir frying) play a key role in children’s acceptance and consumption of vegetables (Poelman and Delahunty, 2011, Poelman et al., 2015, Poelman et al., 2013). Other researchers modified the sensory profile of vegetables by adding ingredients which are known to be liked by children. For example, adding salt (Bouhlal et al., 2013, Bouhlal et al., 2011, Bouhlal et al., 2014), or sugar (van Stokkom, Poelman, de Graaf, van Kooten, & Stieger, 2018) (Sullivan & Birch, 1990) can increase children’s vegetable liking and/or consumption (for reviews see DeCosta et al., 2017, Nekitsing et al., 2018). However, due to children’s already high consumption of sugar (WHO, 2016) and salt (Grimes, Riddell, Campbell, & Nowson, 2013), the latter approach is not favourable for health.
Besides altering the preparation method or adding sugar or salt, vegetable consumption can also be changed by manipulating serving styles (Bergamaschi et al., 2016, Olsen et al., 2012, van Kleef et al., 2015). For example, providing larger unit sizes may increase consumption (Goh, Russell, & Liem, 2017). Several studies in adults have shown that when food is provided in larger unit sizes (e.g., 100 g of small cookies, vs 100 g of large cookies), consumers eat more of the food, even though the total weight of the offered food did not change (Geier et al., 2006, Marchiori et al., 2011, Marchiori et al., 2012). It is theorized that unit bias effect is due to a distorted view of the appropriate unit size (Geier et al., 2006). In adults it has been shown that when presented with a large unit size, adult consumers tend to think that this large size is the norm and has to be consumed accordingly (Geier et al., 2006). On the other hand, when the larger size is divided in smaller units, the smaller unit becomes the norm and consumption decreases (Geier et al., 2006). A related explanation is that the repeated consumption of small units is perceived as more impulsive (and undesirable when offered unhealthy foods) which subsequently limits consumption (van Kleef, Kavvouris, & van Trijp, 2014).
Until recently unit bias effects have been shown for unhealthy snack foods, such as chocolate (van Kleef et al., 2014), cookies (Marchiori et al., 2012), candies (Marchiori et al., 2011) and snacks (Weijzen, Liem, Zandstra, & De Graaf, 2008). These studies suggest that in order to decrease consumption of unhealthy foods in adults, one might want to decrease the unit size of these foods. Potentially unit size bias could also be used to increase the consumption of healthy foods. That is, by providing larger unit sizes of healthy foods this could increase the consumption of those foods. Previous studies investigating this hypothesis, found that when focused on liking size did not matter to children, however actual consumption was not measured (Olsen et al., 2012). Bergamaschi and colleagues did measure intake of different serving styles of fruit and vegetables, but this study was focused on variety (i.e., chunk, sticks and slices of apple and carrots). They found no difference in intake depending on such variety. However, a direct comparison between small and large serving styles of the same vegetable was not made (Bergamaschi et al., 2016).
When the role of unit size and children’s vegetable consumption was investigated, inconsistent findings have appeared. Van Kleef and colleagues could not confirm that children (8–13 yrs of age) ate more of large vs small unit sizes of cucumber in an experimental classroom setting (van Kleef et al., 2015). We recently investigated the unit bias effect for healthy foods in children: we showed that when we provided children with whole carrots, rather than diced carrots as a snack during a short (10 min) snack break, they consumed 10% more carrots, which could be explained by a unit bias effect. An alternative explanation could be a difference in children’s liking of the whole and diced carrots, or, more specifically, how liking decreases during consumption. When foods are consumed, liking declines and consumers get bored by the food. This results in the termination of consumption (Hetherington, 1996). This decline in liking during one consumption period is called Sensory Specific Satiety (SSS), which is defined as the change in liking of a food that has been consumed ad libitum relative to a change in liking of a food that has not been consumed ad libitum (Rolls, 1986). Previous research suggests that large food items are consumed with larger bites than small food items (Spiegel, Kaplan, Tomassini, & Stellar, 1993). This can result in a lower oral exposure and lower level of SSS which consequently influences food consumption (Zijlstra, de Wijk, Mars, Stafleu, & de Graaf, 2009). The role of oral exposure can potentially explain the different findings when unit size effect is testing with cucumber (van Kleef et al., 2015) or carrots (Goh et al., 2017).
Although SSS has been observed in children with the consumption of sweet dessert foods (Olsen, Ritz, Hartvig, & Moller, 2011), our recent research indicated that it did not occur with fresh carrots (Goh et al., 2017). A limitation of that study was, however, that children were only given ten minutes to consume carrots and it could be that a longer period is needed before SSS occurs with a fresh vegetable like carrots. Indeed in our previous study about 50% of the participants indicated that they would have eaten for longer than the set limit of 10 min if allowed (Goh et al., 2017). For these children, then, SSS might occur if they were given more time to consume the carrots. Previous studies which investigated SSS in children, used a design in which children were allowed to eat as long as they wanted until they were feeling comfortably satiated. By applying such design it was shown that children could take up to 90 min to develop SSS and stop eating (Olsen et al., 2011). Other research gave children a set quantity of a particular food and observed SSS after children consume nearly 100 g of a pudding (Birch & Deysher, 1986). An extended consumption period would allow the hypothesis regarding the role of SSS in carrot consumption to be tested. Furthermore, our previous study investigated children in a controlled school setting in which children were closely supervised by individual interviewers while eating carrots and it remains to be investigated if the unit bias effect with carrots also applies to a more real life setting.
The present study aimed to answer the following questions in a real life setting (a) does the size of vegetables (diced or whole) play a role in children’s ad libitum consumption of carrots and (b) does SSS occur when children consume diced or whole carrots.
Section snippets
Participants
Primary school aged children and their parents were recruited through flyers that were placed at public places in Melbourne, Australia. Interested participants called the Centre for Advanced Sensory Science at Deakin University and were screened through a short phone interview. Inclusion criteria were: a) children were aged between 6 and 11 years at the time of testing, b) available at both testing sessions, and c) not allergic to either of the test foods (i.e., carrots and cucumber). The study
Results
Seventy-three children initially started the test. Thirteen children were excluded because they did not attended both testing sessions. This resulted in an initial sample size of 60 children (25 females, ages 8.6 ± 1.6 yrs, BMI:16.5 ± 2.3 kg/m2). Five children (4 girls, 1 boy, 8.8 ± 2.2 yrs. of age) were considered outliers and excluded from further analyses because their consumption patterns of the diced carrots fell more than 1.5 times the interquartile consumption range above the third
Discussion
The present study demonstrated that children’s carrot consumption can be increased by serving carrots as a snack food during entertainment: children ate on average two servings of vegetables while watching a movie. In addition, the results showed that by changing from diced to whole, consumption was further increased. The effect seems to be the strongest within the first 10 min of consumption although the 90 min of consumption did allow a further increase of carrot consumption when carrots were
Acknowledgement
This study was funded by a grant from the Helen MacPherson Smith Trust, Grant ID 6760: Motivating children to consume vegetables. We thank Jimmy Cahayadi for his assistance in the collection of the data.
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