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To compare taste exposure (TE), nutrition education (NE) and TE+NE together on intake of an unfamiliar vegetable (mooli/daikon radish) in preschool-aged children.
Children attending 11 preschools in England were randomly assigned by clusters to four intervention conditions using a 2×2 factorial design: TE, NE, TE+NE, and no intervention (control).
Two hundred nineteen children aged 2 to 5 years participated from September 2016 to June 2017.
The intervention period was 10 weeks preceded and followed by measurements of raw mooli intake as a snack. Preschools were randomized to receive weekly TE at snack time (n=62 children); NE (n=68) using the PhunkyFoods program; TE+NE (n=55) received both weekly taste exposures at snack and lessons from the PhunkyFoods program; and the control condition (n=34), received NE after the final follow-up measurement.
Main outcome measures
Individual measured intakes of mooli at Week 1 (baseline), Week 12 (postintervention), and Week 24 and Week 36 (follow-ups).
Differences in intakes were analyzed by cluster. Logistic regressions were conducted to examine odds ratios for intake patterns.
Data from 140 children with complete mooli intake assessments were analyzed. TE increased intake from 4.7±1.4 g to 17.0±2.0 g and this was maintained at both follow-ups. Children assigned to the NE conditions were more likely to eat some of the mooli than children who were not in the NE conditions (odds ratio 6.43, 95% CI 1.5 to 27.8). Combining TE and NE produced no additional benefit to intake beyond TE alone.
Taste exposures encouraged children to eat more of the unfamiliar vegetable, whereas nutrition education encouraged children who were noneaters to try the vegetable. Both approaches were effective and can be used to produce different outcomes.
Research Question: To what extent do taste exposure, nutrition education, or the two strategies combined lead to increased intake of an unfamiliar vegetable (mooli/daikon radish) in preschool-aged children?
Key Findings: Taste exposure encouraged children to eat more of the unfamiliar vegetable (mooli/daikon radish) and nutrition education encouraged children who were noneaters to try the vegetable. Each approach is effective in a different way: exposure increases consumption of an unfamiliar vegetable in children who are already eaters, whereas education may be needed as part of a more gradual approach to trying an unfamiliar vegetable in noneaters.
Diets containing foods that are rich in nutrients and low in energy density such as fruits and vegetables have protective effects on health.
Children who are fussy eaters appear to be especially resistant to eating vegetables, and it has been proposed that systematic exposure in early life is needed to encourage vegetable intake in these children.
These programs are tailored to the child’s age with learning activities that are designed to be fun and interactive as well as educational. However, education programs implemented in preschool tend to focus on vegetables that are already familiar to the children and their effects on unfamiliar vegetables are understudied.
Therefore, it has been proposed that learning about vegetables through direct experience of the taste, smell, and texture through exposure and engaging children in hands-on activities to increase familiarization will increase intake of vegetables.
Similarly, in preschools, to avoid waste, children may not be offered vegetables that are believed to be disliked. Providing children with incentives such as tangible nonfood rewards (eg, stickers) with repeated taste exposure can increase vegetable acceptance, both in homes and in preschools.
Indeed, combining nutrition education that is specifically designed to increase knowledge about eating vegetables with taste exposures might produce a synergistic effect in increasing vegetable intake. Synergy in this context may be achieved by both encouraging children to try the taste of an unfamiliar vegetable therefore giving them direct experience of the target vegetable (eg, smell, taste, and texture) as well as by increasing their awareness of different vegetables and their benefits to health and well-being. For young children it may be important to understand why vegetables are good for them to also taste and eat them when offered. Therefore, the aim of this cluster randomized trial was to test the relative efficacy of repeated taste exposure (TE), nutrition education (NE), and a combined TE+NE intervention compared with a no-intervention control on intake of an unfamiliar vegetable in preschool-aged children. The primary hypothesis was that children would increase intake of an unfamiliar vegetable following intervention relative to control and that TE+NE would enhance intake of the vegetable more than either intervention alone relative to a control.
Materials and Methods
A 2×2 factorial parallel design (with a no-intervention control) was used in the present cluster randomized controlled trial (Figure 1). For ease of intervention delivery and feasibility in a preschool setting, it was decided that a cluster randomization trial was the most appropriate design. The 11 preschools agreeing to participate in the study varied in size; therefore, stratified randomization was used. The preschools were divided into three strata, with the four largest in one stratum, then the four smallest in another stratum. One preschool in each stratum was assigned to each intervention condition using an online list generator (https://www.random.org/lists): TE, NE, TE+NE, or no intervention (control). Researcher CN generated the random allocation sequence for each preschool and preschool managers chose the day and time that was most convenient for them, and thus which children would be included in the study. Preschool managers were not informed of their condition allocation until all preschools were recruited (after consent) and randomized. It was possible to conceal condition allocation between clusters but not within a cluster. Parents were given a list of potential study vegetables used during the study phase.
Preschools were offered the PhunkyFoods program (PFP; https://www.phunkyfoods.co.uk/about-us/programmes/) as an incentive to take part (normally valued at £395 per annum). They either received this during the intervention or on completion of the study. All procedures were conducted in accordance with the ethical guidelines set by the British Psychological Society and approved by the University of Leeds, School of Psychology Research Ethics Committee (no. 16-0198). The trial was preregistered with ClinicalTrials.gov (identifier: NCT03003923). The study lasted for 12 weeks (September 2016 to December 2017), including a 10-week intervention phase (plus baseline and postintervention assessment) with follow-up intake of the unfamiliar vegetable measured at Week 24 (March 2017) and Week 36 (June 2017).
Fifty-five preschools from Leeds, Brighouse, and Halifax (West Yorkshire, UK) were sent a recruitment e-mail in July 2016, followed by a telephone call. In all, 219 children were enrolled in the study; however the anticipated sample size was not fully met for the final analysis (Figure 2). The low number of children in the control condition was attributed to low attendance on different test days. Consent to participate was sought from the preschool manager at the cluster level and individually by parents using an opt-out approach. Preschool managers signed the informed consent form and children could say no and decline to participate in research activities. All children aged 2 to 5 years attending their preschool class on the agreed test day were included. They were excluded from the study in the case that they had any relevant food allergies, a medical condition that would prevent them from eating the test vegetable, or if their parents opted out of the study (see Figure 2). Included in the final analysis were 140 children (70 boys and 70 girls) with complete intake assessments at all four time points with a mean age of 40.6±0.4 months. Preschools were eligible to take part in the case that they were not participating in other nutrition health programs and were able to commit to the time frame of the study (9 months).
Table 1 provides the baseline characteristics of children who took part in the intervention. There were no differences across intervention conditions in sex distribution or mean body mass index z score, but there were differences in mean age. No differences were found in baseline characteristics or intake of the children who were lost to follow-up compared with those who completed the study.
Table 1Characteristics of preschool-aged children allocated to one of four conditions, including baseline intake of the unfamiliar vegetable (mooli) (N=140)
During development of the intervention, all preschool managers were asked about vegetables offered to children. Based on this information a selection of seven unfamiliar vegetables, available through all seasons in the United Kingdom, were selected for a taste test (coccinia cluster beans, steamed beetroot, raw beetroot, marrow, cherry belle radish, and mooli white radish). These vegetables were tasted and independently rated by a panel of 10 researchers. The purpose of the tasting session was to identify a novel vegetable (ie, unfamiliar) that could be eaten raw (ie, not too bitter or hard) and was suitable for preschool-aged children. Through this process, mooli (a variety of daikon, a long white radish) was selected as the unfamiliar vegetable.
The preschool staff members were provided with all the necessary resources and basic instructions to deliver the intervention to children in their preschools. During Week 1 baseline intake of mooli was measured at the prearranged snack time and children’s height and weight was also measured. Over the next 10 weeks, children in the intervention conditions were offered either the TE, NE, or TE+NE intervention and children in the control condition were offered no intervention. After the intervention at Week 12 (postintervention) mooli intake was measured at snack time. Mooli intake was also recorded at two follow-up periods (Week 24 and Week 36) at the usual snack time. The intervention was delivered at the level of the preschool and outcomes measured at the individual level.
Baseline, Postintervention, and Follow-Up Intake Assessment Procedure
Intake of mooli was assessed at Weeks 1, 12, 24, and 36. The vegetable was offered to children at their usual snack time (mornings or afternoons) so it was assumed that children would be moderately hungry. Each vegetable portion was weighed (to the nearest 0.01 g) before and after each snack time using a digital scale (Mettler PJ4000; Mettler-Toledo LLC) by the research team. Fresh mooli was peeled and cut into bite-size pieces (thin ∼0.4-mm slices, in circles, semicircles, or quadrants depending on the size of the mooli). Snack bags were prepared and weighed for each child with a ∼40-g portion. Spare bags were prepared in case children requested more of the vegetable. Study snacks were delivered to the preschools at least 30 minutes before their snack session to allow staff time to prepare for this. Children were allowed to eat ad libitum during each snack time. Staff members were asked to ensure that children did not share their snack with others and that any leftovers were returned to the individual snack bags. Staff were advised to store the vegetable in a refrigerator or the cool bag provided and to return the bags to the cooler after consumption. This was done to reduce moisture loss. Snack bags were collected after the exposures and were reweighed immediately to calculate intake.
For the TE and TE+NE conditions, the researcher prepared mooli as snacks, delivered this to each preschool, and the snacks were provided to children by preschool staff members. The procedure for mooli preparation and intake were same as those on the intake assessment days (see above). TE involved offering mooli during usual snack time once per week, every week for 10 weeks (Weeks 2 to 11). The vegetable snack was offered in preweighed 40-g portions using individual snack bags labeled for each child.
For the NE clusters, preschool staff members were trained by the PhunkyFoods team to deliver the existing nutrition education program (www.phunkyfoods.com). The PFP is designed for preschool-aged children and follows the English Early Years Foundation Stage Framework, promoting learning through planned purposeful play, and a mix of adult-led and child-initiated activities. PFP provides preschools with ideas and inspiration for classroom carousel play activities (eg, stories, role play, and games), practical food handling/preparation activities, educational displays for the classroom and parental involvement opportunities. Resources are available in both online and offline formats, and cover a range of nutrition education topics. For the NE clusters, staff members were instructed to teach two specific components of the PFP as often as possible during the 10-week period: Eat Well and Strive for 5!, then to record these activities on a checklist. Staff members were given materials to support their teaching within the curriculum covering communication and language, physical development, literacy, expressive arts and design, food preparation, and display themes. These included photo cards, posters, a floor mat, game ideas, interactive video stories, music, food preparation, tasting ideas, and drawing and coloring activities. For the Eat Well component, children learned about eating a well-balanced diet, adapted from the Eat Well guide and in Strive for 5!, children were taught about eating five portions of fruits and vegetables each day as well as the importance of eating a variety of these foods. The PFP does not contain any activities directly relating to mooli.
The checklist consisted of 12 activities for each of the two modules (24 possible). Using this checklist, staff members identified which of the 12 activities they used in lessons from the module and this was converted to a percentage to indicated coverage of the materials. In total, six preschools using the PFP delivered at least 35% or more of the required contents (delivery of the intervention was 100% (n=2), 50% (n=2), 40% (n=1), and 35% (n=1). Preschools in the NE clusters were able to continue accessing and delivering the PFP during the postintervention period, reflecting pragmatic and real-world delivery access.
For the TE+NE intervention, children were offered both weekly taste exposures and the education program (described above). The control condition did not receive any intervention during the study period but were offered the education program on completion of the study (after Week 36).
Data Collection and Measures
Primary Trial Outcomes
The primary prespecified outcome was weighed intake of mooli. All children across conditions were offered the mooli at four time points: baseline (Week 1), postintervention (Week 12), follow-up 1 (Week 24), and follow-up 2 (Week 36). The outcomes were measured at an individual level because factors such as body mass index, age, and eating traits may affect vegetable intake and vary among children.
Other Measures: Demographic and Anthropometric Characteristics
The investigator measured height using a stadiometer (Seca 217; Seca) and weight using a portable weighing scale (Seca 878). Body mass index z scores (adjusted height and weight for age) were calculated using the World Health Organization anthropometric calculator (http://www.who.int/childgrowth/software/en). Child age and sex were recorded by preschool staff members. Eating status (eater or noneater) was used as a proxy for fussiness as it is defined in relation to the child’s actual behavior (ie, willingness to try the vegetable).
Intervention Evaluation Measures
As part of the process evaluation, preschool staff members were asked to complete feedback surveys regarding the intervention. Members of staff from nine preschools (excluding controls) were asked to rate the materials on the following items: acceptability, user engagement, implementation and effectiveness of the taste exposures, and/or PFP depending on condition. The survey consisted of items with a Likert scale ranging from 1 to 10 (where 1=extremely negative and 10=extremely positive).
Descriptive statistics (mean±standard error) were generated for demographic variables and to plot the pattern of intake by condition over time. Univariate analyses of variance were used to test for differences in demographic characteristic variables across conditions. In addition, intake data were excluded from analyses where children in the TE conditions had fewer than five taste exposures (n=3). Also, for this condition because intake was measured weekly, in the case that the data were missing for the baseline (n=6) or postintake (n=17) the child’s very first or the final intake was used for the analysis. Children in the NE and control condition with missing intake data at baseline or postintervention and any children’s data missing for Follow-up 1 or Follow-up 2 were excluded from the main analysis (n=75). One child who ate 121 g test vegetable at postintervention (in the TE+NE condition) was an outlier (ie, extreme value on the box plot) and was excluded from the analysis.
Because children were recruited using a cluster design, it was important to account for the influence of cluster assignment. In addition, for repeated measures, each data point was clustered within child. Therefore all the models described below corrected for this using the complex samples procedure within SPSS version 24
to incorporate the contribution of these variance components to the data.
Intake data for all time points resulted in a positive skew as many children ate 0 g mooli. Therefore, a complex samples logistic regression analysis was conducted to examine what factor predicted children eating at least some of the mooli (classed as eaters). Next a complex samples general linear repeated measures analysis of variance was performed to examine the predictors of the amount consumed, when children had eaten some of the mooli. In particular, among the children who had eaten some mooli at baseline, the effects of condition (TE, NE, TE+NE), time of follow-up (immediately postintervention, 3-month follow-up, 6-month follow-up), and their interactions were tested for effects on intake, controlling for age and baseline consumption.
All analyses were performed using SPSS version 24.
Intakes from baseline to postintervention for all conditions are shown in Figure 3. However, given that many children did not eat mooli at baseline, the data were significantly skewed and not suited to simple parametric analysis. Therefore, children were categorized according to their eating pattern at postintervention, Follow-up 1 and Follow-up 2 (noneater, eater) and these are shown in Table 2.
Table 2Distribution of preschool-aged children by eater status across study conditions
Logistic regression indicated that at postintervention, there was an interaction between TE and NE (χ2=4.67, P=0.031), which indicated that children in the control condition were less likely to be eaters than in any of the other conditions (OR 0.20, 95% CI 0.05 to 0.87). In particular, children in the NE conditions had higher odds of eating the mooli than children who were not in the NE conditions (OR 6.43, 95% CI 1.5 to 27.8; χ2=5.73; P=0.017). TE did not affect whether or not children were classified as eaters (OR 1.65, 95% CI 0.37 to 7.44; χ2=0.24; P=0.63). There was no main effect of time on eater status (χ2=5.82; P=0.054).
A second analysis was conducted to examine, only in those children who ate the mooli, what predicted their intake (Table 3). In this analysis, significant effects of condition were found indicating that intake increased significantly in the TE condition (F[1,135]=11.21; P=0.001). There was also a main effect of time (F[2,134]=9.02; P<0.001). There was no significant effect of NE (F[1,135]=0.47; P=0.49) and no significant interactions (largest F=1.17). Contrasts revealed that the significant effect of time was due to children eating more at follow-up 2 than at postintervention (t=2.20; P=0.029). Overall, within the TE conditions, 10 exposures were sufficient to increase average intake by ∼10 g, which represents a quarter of a portion (on average) of a child’s vegetable intake, or 5% of their daily fruit and vegetable recommendation. This change was maintained up to 6 months after the intervention phase.
Table 3Amount eaten of the unfamiliar vegetable (mooli) among children categorized as eaters (>0 g intake) at each time point by intervention condition
For the TE intervention, four out of five preschools reported that the intervention was easy to deliver and those four preschools also reported that children were engaged during the TE sessions. However, only two out of five preschools agreed that they were able to integrate study requirements within their normal preschool curriculum. Cost and time were the main barriers to implement repeated TE intervention in preschools. Some preschools reported that they found it challenging to get some children to try the new vegetable, and some preschools did not comply with the TE protocol because the staff continued to offer the usual snack immediately after the vegetable snack. Three out of five preschools noticed an increase in intake of the test vegetable over the intervention period. For overall experience, ratings from five preschools ranged from 5 to 10 on the 10-point Likert scale.
NE Intervention Feedback
Overall feedback for the NE intervention was very positive. All six preschools reported that the PFP resources were of a high quality. Five out of six preschools reported that resources were easy to use, easy to deliver to preschool-aged children, and engaging for the children. While five out of six preschools reported that they believed that the implementation of the NE program had an influence on healthy lifestyle awareness and knowledge of the children, four out of six preschools reported that the program did not have any influence on improving children’s healthy eating behaviors. One preschool allocated to NE recognized the importance of the taste exposure technique. They commented that children did not receive enough exposure to the study vegetable and suggested improving the program by offering the children more exposure to the vegetable as part of NE.
To our knowledge, this is the first trial to examine the efficacy of both a taste exposure and nutrition education intervention delivered together or in isolation on intake of an unfamiliar vegetable in preschool-aged children. In partial support of the first hypothesis, findings from the present study confirmed that among children who ate some of the vegetable, repeated taste exposure was an effective method to increase intake of mooli. Thus, following 10 exposures, children who were willing to consume the vegetable at baseline learned to accept more of this vegetable over time and this was sustained long-term when offered the same vegetable again. In addition, education increased willingness to try mooli among children who began the intervention as noneaters. However, there was no additional benefit to overall intake in our TE+NE condition.
Children who were classified as eaters increased their intake of the unfamiliar vegetable during the postintervention period. This might be attributed to mere exposure effect, because by the end of the study all children had received a minimum of four exposures to the unfamiliar vegetable.
found that effects of taste exposure alone (without rewards) became nonsignificant by 3 months. These differences may be attributable to use of a previously disliked rather than an unfamiliar vegetable and to differences between using a home-based rather than a preschool setting for the study. Also, these differences suggest that rewards may be needed in the case that the effects are to endure in the home environment but may not be necessary in preschools where other motivating factors such as peer modeling and social norms are present, in line with predictions form Social Learning Theory.
Nutrition education is widely used in preschools; however, the present study demonstrated that learning in a general way about vegetables is not sufficient to increase intake of an unfamiliar vegetable. Rather, it sets the scene for children to try the vegetable. Previous studies have found that learning specific to a target food, such as through visual exposure using picture books or sensory learning, can be effective in increasing intake of a target vegetable.
Therefore, there may be some benefit to combining nutrition education with experiential learning about the target vegetable with taste exposure so that a more gradual, step-by-step approach is adopted. This approach might involve a first step of introducing vegetables in a general way through nutrition education followed by experiential and sensory learning, and finally taste exposure. A more gradual approach may tackle children’s food avoidance behaviors. For example, a study with children aged 7 to 9 years found that an integrated educational intervention involving taste education and culinary experience reduced children’s food neophobia and increased their willingness to try novel foods.
Therefore, taste exposures could be integrated into existing nutrition education programs, but more work is needed to understand how the delivery of taste exposure can be improved because only two preschools in the present study were able to integrate this into their usual curriculum. The use of picture books highlighting a target vegetable may help to facilitate taste exposures and this is an ecologically valid method to apply in preschool settings.
The strengths of this study include randomization, allocation concealment, reduced selection bias (by using an opt-out approach at the individual level), objective data collection, and a long-term follow-up. However, study results should be considered in the context of some limitations. First, a reasonable sample size was recruited; however, due to the nature of the study design there was a high rate of missing data over time for the complete set of intake data, including follow-ups (36%). As a result of this, there was a substantially smaller sample size in the control condition. In terms of the intervention delivery, preschools varied in the extent to which they delivered the two components of the NE program and compliance was recorded using self-report from preschool staff. This is in line with previous research that suggests that barriers exist in implementing nutrition education interventions; hence, they may be used infrequently or assigned low priority in an already crowded curriculum.
Nutrition education programs as used in the present study are generalizable to the real world where implementation is variable. Similarly, some preschools did not comply with the repeated taste exposure protocol because the staff continued to offer the usual snack immediately after the vegetable snack. Despite this, the effect of taste exposure was still evident in the preschool context. Future research should assess the effects of these interventions on the intake of the target vegetable as well as other unfamiliar and familiar vegetables at home. It is also important to investigate transfer effects; for example, from preschool to home and vice versa. Children’s food fussiness influences eating behavior change and this can affect the success of a dietary intervention. Therefore, adjusting an intervention to suit the individual needs of children, including noneaters or fussy eaters, could improve the success of taste or education-based interventions.
Taste exposure is a robust and durable strategy to promote intake of an unfamiliar food. In this study, preschool-aged children who were willing to eat an unfamiliar vegetable increased their intake of this vegetable over time following intermittent exposure during snack time in a group setting. In contrast, nutrition education alone was not sufficient to increase intake of a novel vegetable. However, nutrition education was sufficient to increase willingness to taste the unfamiliar vegetable. Therefore, in future, such programs could incorporate experiential learning (including taste exposure) to encourage first steps toward tasting and eating a new vegetable.
For more information on the subject discussed in this article, see Sites in Review on page 2147.
The authors thank preschool staff, parents, and children for their contribution and time in this research study. The authors also thank Alexandra Campbell from the PhunkyFoods Programme for writing the story for the storybooks.
C. Nekitsing, P. Blundell-Birtill, and M. M. Hetherington formulated the research questions and designed the study and were responsible for study oversight. C. Nekitsing conducted the research. C. Nekitsing and P. Blundell-Birtill performed the statistical analysis. C. Nekitsing drafted the manuscript and all authors contributed to this. All authors read and approved the final manuscript.
C. Nekitsing is a doctoral degree research student, School of Psychology, University of Leeds, Leeds, UK.
P. Blundell-Birtill is an associate professor of psychology, School of Psychology, University of Leeds, Leeds, UK.
M. M. Hetherington is a professor of biopsychology, School of Psychology, University of Leeds, Leeds, UK.
J. E. Cockcroft is director, Purely Nutrition Ltd, Harrogate, UK.
Published online: August 01, 2019
STATEMENT OF POTENTIAL CONFLICT OF INTEREST No potential conflict of interest was reported by the authors.
FUNDING/SUPPORT This research is funded by a White Rose Doctoral Training Centre (WRDTC) Economic and Social Research Council (ESRC) Collaborative Award. The collaborative partner is Purely Nutrition Ltd. Contribution in kind, which includes storybooks and photo cards, were received from Purely Nutrition Ltd.