Love-it or hate-it, kale can be a divisive vegetable at the dinner table, but a new study has shown fetuses encountering it in the womb are more likely to grimace than smile when they taste it.
The research team, led by Durham University’s Fetal and Neonatal Research Lab, gave pregnant mothers capsules of either carrot or kale and used 4D ultrasound scans to monitor the facial responses of their unborn babies.
Fetuses reacted with more “laughter-face” expressions when exposed to a carrot flavour, and more “cry-face” expressions when their mother ate kale capsules.
The team analysed the scans frame by frame to look at the movement of over 30 facial muscles. Movements associated with the “cry-face” expression included furrowed brows and turned down mouths, while “laughter-face” had cheek and lip movements that resembled smiles.
Their study is published in the journal Psychological Science. Co-author Professor Nadja Reissland says that this is the first time babies’ responses to food have been captured in utero.
“We do know that the origins of food preferences begin very early in life, basically in the womb. We wanted to actually find the proof that we could see reactions in the womb.”
It is thought that the babies were responding to both taste and smell. The unborn babies in the study were from 32 to 36 weeks gestation. Fetuses’ taste buds function from 14 weeks, and their olfactory senses (smell) mature at 24 weeks.
Even though they are in the liquid environment of the womb, when they swallow, amniotic fluid passes over receptors in their nose that sense smells.
Cautions
It is tempting to draw conclusions that the expressions meant the babies were happy or upset, but Reissland cautions against going that far.
“We do not know the connections between the muscle movements - the expression - and the feeling state of the fetus.”
She says the babies’ responses to kale was a reaction to the surprise of a novel, and bitter, flavour, rather than signalling a hatred for the vegetable.
“Their reaction was this very strong [expression], which we could think of as negative expression, but I don’t think we can call it negative it’s more of a surprised expression.”
One explanation that Reissland gives for why they frowned and grimaced at kale is that it’s an instinctive response, but one that can be changed through repeat exposure.
“Normally bitter taste is associated evolutionarily, with poison. So, you should avoid it. [You can] get the fetus to learn that the bitter taste is not poisonous but is actually something that is edible and good for you.”
Reissland says that by experiencing the flavours of their mothers’ diet prenatally, it could be that babies’ are being socialised to be more tolerant of the foods they will be likely to encounter once born.
The research team have a follow-up study underway with the same group of babies post-birth, to test whether the flavours they were exposed to in the womb influences their willingness to try different foods.
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