Gertrude Zeinstra says Repetition Is The Key
There is near unanimity on the desirability of children eating more produce. But when one looks at the initiatives actually done, almost all wind up getting children to eat more sweet fruit and calling it a victory.
The problem, of course, is that many of the healthiest elements of produce consumption come about through consuming more vegetables. When we learned of a researcher focused on this area, we asked Pundit Investigator and Special Projects Editor Mira Slott to speak with Gertrude Zeinstra of the Consumer Science Department at Wageningen University in the Netherlands to find out more:
Q: What are the key points you can shed on your study?
A: What I think is important to point out is that for children, there is often a large difference between fruits and vegetables. We have an inborn preference for sweet, so usually fruit is quite liked by children, whereas vegetables are often not.
We also have an inborn tendency to like foods with a lot of energy, and vegetables do not contain a lot of energy. So, that’s also a reason why we probably don’t like vegetables that much right from the start.
Q: How do we go about tackling that challenge?
A: We know taste is very important. In general, children won’t eat something they don’t like, even if it will have a positive impact, or relieve pain. For instance, if they have an earache and the medication is not-so-nice tasting, they will not take it, even if you explain it will be good for their ear and make the pain go away. It’s difficult. In our research, we looked at known strategies for increasing children’s likings of food, and we studied whether these strategies could be applied to vegetables.
First, we conducted a qualitative study with three age groups from primary school representing different cognitive development stages, and a parental survey study.
In this parental questionnaire, we wanted to see what Dutch parents were doing to increase their children’s fruit and vegetable intake. Here we also found a difference between fruits and vegetables. The atmosphere around vegetables was more negative than for fruit, mainly because there was more pressure put on the kids to eat the vegetables. We know from the literature that using pressure to get kids to eat certain food items is often counter-productive.
These initial studies indicated parents who give their children a choice or some kind of autonomy with eating fruits and vegetables have children who eat more fruit and vegetables. Texture is also an important factor. We know from literature that raw vegetables are often easier for children, and they don’t like very slippery or mushy vegetables, such as asparagus or mushrooms, but cucumber or raw carrots are usually OK. In our study, texture was more vital for 4 to 5-year-old’s food preferences than for 11- to 12-year-olds.
We then conducted three intervention studies, focusing on vegetables.
Q: Could you walk us through the methodology, how the studies worked, and what you learned, etc.?
A: We wanted to explore the effects of different preparation methods. We had carrots and French beans prepared using six different methods — mashed, boiled, steamed, grilled, stir-fried and deep-fried — to see which the children preferred most and least, in a ranked order. An adult panel scored the six preparations on their appearance, taste and texture characteristics.
We found steamed and boiled were most appreciated by the kids, and boiled is also the most familiar method in the Netherlands. Familiarity is also important for children’s food choice; they are often reluctant to try unfamiliar foods. We found when the appearance of the vegetable is uniform, it positively influenced their liking.
This was also the case for a crunchy texture. Whereas, when there was brown coloring on the vegetables due to the preparation, it negatively influenced their liking. When the texture was granular (mashed with pieces inside), that was not really liked either. So, the advice is if a child doesn’t like a certain preparation, try another.
Q: What other factors did you consider?
A: We wanted to test in an experiment whether choice and autonomy would influence intake. If you offer children a choice of vegetables, will it increase their consumption? We conducted a study with 300 children. Each child was invited with one of his/her parents to have dinner in a restaurant. For each child, two target vegetables were selected that were similarly liked by the child. One hundred children in the control group didn’t have a choice, and just got one vegetable. One hundred had a choice between the two vegetables, and the other group had both of these vegetables on the plate, thus having choice and variation. We measured consumption and how much they liked the vegetables.
Q: Did the results meet your hypothesis?
A: Unfortunately, we did not see any difference in their intake. In addition, we found no difference in the liking of the vegetables.
Q: At one of our past New York Produce Shows, Gabriella Morini, a taste and food sciences professor and researcher at the University of Gastronomic Sciences in Pollenzo, Italy, presented research on the molecular aspects of taste, and argued the need to condition taste receptors, which are naturally opposed to bitter vegetables, starting at an early age, preferably when the child is in the womb. And studies have found that children may require multiple repeated tastings of a vegetable before liking it, due to their developing and changing taste buds. Did this phenomenon play into your research?
A: This repeated tasting is one of the key findings. Most of these repeated exposure studies have been done in very young children when eating their first solid foods. When introducing new vegetable tastes, repeated exposure is very important to make the child familiar with the taste.
Repeated exposure has been compared with other conditioning mechanisms. One of those mechanisms is pairing a new taste vegetable with a high-energy food such as a sweet fruit, usually resulting in higher liking. It’s an important question to ask if this works also for vegetables to use high energy as a bridge to liking. The other mechanism is to pair an unfamiliar taste with a liked sweet taste. Various studies have been done with these three mechanisms.
Q: Are these conditioning mechanisms effective when applied to vegetables?
A: Repeated exposure is the key. Adding energy or adding sweetness was not really necessary. So, repeated exposure is very effective for unfamiliar/novel vegetable tastes. But what can we do to increase consumption with more familiar vegetables? When children are 3 or 4 years old, they’ve already learned, ‘this is a vegetable I like, and this is one I don’t.’
Q: Have you weighed the influence of biological factors with environmental and social factors?
A: Yes, we often look at the whole picture; eating behavior is very complex. For example, role modeling is a very important influence. In many studies, parental intake is a strong predictor of children’s intake. For this project, we did a role-modeling study with child idols that took place at the schools. We played a movie where a role model was eating vegetables enthusiastically, and we did several exposures to the vegetables and the movie. There was not an immediate effect of higher intake due to the intervention.
What we did find, though, was the kids who were exposed to these role-model movies had a higher intake compared to the children in the control group over an extended period of time when we later measured intake of the children again.
The study is challenging because there may be a delayed effect from the intervention. In future research, it is important to take into account direct and delayed effects. Especially with children who develop in steps, it is possible delayed effects may occur.
Q: Could you elaborate on the complications of studying delayed effects? Aren’t there many variables, which also differ from child to child?
A: Definitely. It is impossible to control for all impacts that influence consumption. There is also a technical side. It is costly to do a study where you follow children over time. Also, children vary a lot in their vegetable intake, so if you want to measure accurately, you have to measure at an individual level, what you give them, and the actual amount of what they consume at the different stages of the process. Therefore, longer-term studies also require money.
In the Netherlands vegetables are practically only eaten during dinner, so the recommended amount is hard to consume in one eating moment. In the Netherlands, we should try to increase the number of eating moments for these vegetables. Also for children, it’s quite a high amount to eat in one single session, and parents are eager for children to eat healthfully, so there will be pressure for them to eat all their vegetables. It would be better to spread out eating moments with snacks in between meals.
Q: Did you undertake a study to test this strategy?
A: We developed a project called Veggie Time in various daycare centers. In the Netherlands, in the morning around 10 or 11 a.m., it’s fruit time, but there is no such moment for vegetables. We knew repeated exposure was such a strong mechanism. We thought it would be good to conduct an experiment in a natural setting. We chose three different unfamiliar vegetables for the experiment.
We had a control group and an intervention group, where we pre-measured their intake of these three vegetables. Then the intervention group had an exposure period of five months where they had these three vegetables offered repeatedly, in various product forms, where the control group did not have exposure to these three vegetables. After the five months, we went back and measured intake in the intervention and control group. We saw for two of the three vegetables, the children in the intervention group increased their intake quite nicely compared to the control group.
Q: What were the three vegetables, and why were just two out of three a hit with the children?
A: We used pumpkin, white radish and zucchini. Pumpkin and white radish showed an increase in intake. With the zucchini, we didn’t see the intake increase or decrease; it remained stable. This could be due to the blander taste of zucchini, or to the fact that — we also checked with the parents — zucchini was more often on the menu, so more familiar than expected beforehand.
Q: You said familiarity was an appealing trait for children. Yet, you found the increased intake with the less familiar items?
A: Yes, in general, familiarity is a positive trait, but there is a difference between willingness to eat and increasing intake. Familiarity is a positive predictor of children’s intake; when offered a choice, most children will choose familiar foods. But when products are unfamiliar, repeated exposure is a very effective mechanism to increase liking and intake.
Q: Is availability and presentation half the battle?
A: Making produce available is very important. Usually, children like fruit, and if you put it in front of them, they’ll eat it. If you put cookies in front of them, they’ll eat those as well. But additionally, the item should be accessible. If a young child eats his apple without the peel and cut in slices, then a complete apple is not accessible to this child. This is necessary to take into account.
Ready-to-eat is great for the children and easy for the parents to provide to the children. That’s indeed very important.
Also, it should not only be about health as a selling argument because young children don’t understand this term; it’s too abstract for them, and several studies show children may associate healthy with distaste. So, it’s better to focus on fun and pleasant.