Over a five-month period, Dutch researchers from Wageningen University Food and Biobased Research gave 250 children, boys and girls, a choice of vegetables.
Using three less frequently eaten vegetables with different tastes - pumpkin (sweet), courgette (neutral) and white radish (bitter) - they assessed liking and willingness to try by measuring the amount eaten or frequency of placing food in the mouth.
The children, aged around two, were given one vegetable per day as an afternoon snack in different formats, such as soups or cracker spreads, to prevent boredom. Salt, spices and olive oil were added but “kept to a minimum to ensure that the vegetable taste was not disguised by other ingredients” while radish was served raw.
Only one in five two to three-year-old children in the Netherlands meets the recommended vegetable intake of between 50 and 100 g per day – which itself is the lower limit of government dietary advice.
The results showed a significant positive effect of the repeated exposure intervention for two of the three vegetables. For pumpkin, intake increased by 88% among intervention children, with no increase in the control group.
For white radish, both intervention and control children increased their intake over time, but the increase in the intervention group was "significantly larger". Courgette intake, however, remained stable in both conditions and there was no repeated exposure effect. This was possibly because of its neutral taste, which “may not have been distinctive enough to have a repeated exposure effect”.
'One size does not fit all'
“In conclusion, repeated exposure to unfamiliar vegetable tastes over a longer period of time in the daily routine of a childcare setting can be effective in improving both children's willingness to taste and their intake of these vegetables,” write the authors.
“However, we also observed that repeated exposure is not always a successful strategy for increasing children's vegetable intake, because, in the current study, we observed no effect for courgette, which is slightly more often offered at home (although possibly not eaten), and blander tasting.
"This implies that one size does not fit all and that additional strategies are needed for frequently offered or eaten and bland-tasting vegetables.”
The researchers had expected to see the largest effect for pumpkin because of its sweet taste, but while the effect was “significant and substantial”, it was not the largest.
Radish intake also increased more than expected (in spite of its bitter taste), with the researchers suggesting the crispy texture of thin radish slices was appealing to kids.
Repeat exposure to healthy food is a valuable technique thanks to its simplicity and low cost. “The absence of parental stress and pressure during such vegetable eating moments may be an advantage for children's vegetable liking and intake,” they add.
Other research backs up the theory of focusing on individual vegetables to increase liking of vegetables among children in general. In a study published in Appetite Journal, UK scientists found that slowly introducing babies to purees made up of one vegetable only – they tested carrots, green beans, spinach and broccoli - made the babies more receptive afterwards to trying and liking others.
“The strategy [of mixing vegetables or masking them with other flavours] probably does not allow for familiarisation with the visual, olfactory, gustatory or textural properties of vegetables,” they write.
Taste preferences can also be influenced by the mother’s diet when the baby is still in the womb, and researchers from Yale University found the impact could be even more profound than taste alone.
They found that a poor maternal diet during pregnancy that is high in salt, sugar and fat can ‘rewire’ regions of the baby’s brain responsible for metabolism control, setting the child up for a lifelong risk of obesity.
Source: Appetite Journal
“Is repeated exposure the holy grail for increasing children's vegetable intake? Lessons learned from a Dutch childcare intervention using various vegetable preparations”
Available online ahead of print, doi.org/10.1016/j.appet.2017.11.087
Authors: Gertrude G. Zeinstra, Milou Vrijhof and Stefanie Kremer