Young children have long-lasting memories of vegetable smells experienced in the womb

Young children are less likely to react negatively to the smell of vegetables they were repeatedly exposed to pre-birth, according to a new study.

Researchers, led by Durham University, UK, say their findings could have implications for establishing healthy eating habits in children.

They examined the facial reactions of three-year-olds to the non-bitter smell of carrot or the bitter smell of kale.

This followed two previous studies when the researchers recorded the reactions of the same children to carrot or kale - first before birth using ultrasound, and then again in the weeks after birth.

They found that the three-year-olds whose mothers had taken carrot powder capsules as part of a controlled experiment when pregnant were less likely to show negative facial reactions towards the smell of carrot.

Similarly, those whose mothers had taken kale powder capsules while pregnant reacted less negatively to the smell of kale.

The researchers say their latest finding supports the argument that exposure to flavours in late pregnancy can result in long-lasting odour or flavour memory in children.

They add that experiencing bitter or non-bitter flavours before birth can shape taste likes or dislikes after being born.  

The researchers say further work would be needed to see if the effect of prenatal exposure on children’s facial responses to vegetable odours has a meaningful effect on vegetable consumption. 

The study is published in the journal Developmental Psychobiology.

Lead author Professor Nadja Reissland, of the Department of Psychology, Durham University, said: “We first observed these children before they were born, at 32 and 36 weeks gestation, using ultrasound scans and then again at about three weeks of age before observing them once more at age three.

“Each time, we coded their facial expressions when exposed to either the carrot or kale flavour or smell.

“What we see over time is that the children are still more favourable to the vegetables they were exposed to while they were in the womb.

“From this we can suggest that being exposed to a particular flavour in late pregnancy can result in long-lasting flavour or odour memory in children, potentially shaping their food preferences years after birth.”

In the latest study, researchers were able to follow up 12 three-year-olds who had taken part in the pre-birth and newborn studies. Each child’s mother had taken either carrot or kale capsules while pregnant.

Wet cotton swabs dipped in either carrot or kale powder were held under each child’s nose.

Their reaction to the different smells was captured on video. The children did not taste the swabs.

The team then analysed the footage to examine the children’s facial reactions – either “laughter face” or “cry face” – and compared these with the reactions seen before birth (32 and 36 weeks gestation) and when they were newborns (three weeks old).

In the pre-birth study, fetuses exposed to the carrot flavour showed more “laughter-face” responses while those exposed to the kale flavour showed more “cry-face” responses.

When studying the children at three weeks, those whose mothers had taken carrot powder capsules while pregnant were more likely to react favourably to the smell of carrot. Likewise, babies whose mothers had taken kale powder capsules while pregnant reacted more positively to the smell of kale post-birth.

In the latest study, when looking at the children at age three, the researchers found a significantly reduced rate of negative facial expressions in response to the odour the children had been exposed to in the womb.

They say this indicates that the sensory experience of babies in the womb continues to influence how they respond as young children.

The study also included researchers from Durham University’s Department of Mathematical Sciences, Aston University and the University of Cambridge, UK; Radboud University Medical Centre, the Netherlands; and the Centre for Taste, Smell and Feeding Behaviour Science, sponsored by the French National Center for Scientific Research (CNRS), and the University of Burgundy in Dijon, France.

Co-author, Dr Beyza Ustun-Elayan, of the University of Cambridge and Radboud University Medical Centre, said: “These findings open up new ways of thinking about early dietary interventions, suggesting that flavours from the maternal diet during pregnancy may quietly shape children’s responses to foods years later.”

The research was funded by a grant from Aston University.

Co-author, Professor Jacqueline Blissett of Aston University, said: “These findings give further support to the use of pre-natal exposure for improving children’s acceptance of often disliked vegetables.”

Fellow co-author, Dr Benoist Schaal, from CNRS, said: “This study confirms that human fetuses can sense the flavours of foods that pregnant mothers eat, which might affect what they will like for years after birth. Research is needed on other odorants and how they affect the fetus and child."

The researchers acknowledge that they were only able to follow a small number of participants from fetal stage to three years of age.

They add that when they were testing newborns it might have been better to do so just after birth rather than at three weeks when they might have had breastmilk exposure to either carrot or kale.

They also acknowledge they did not test for other factors, including genetic influences on taste perception, which might have influenced their results.