Babies develop food preferences in the womb, study suggests

Babies show positive responses to the smell of foods they were exposed to in the womb after they are born, according to a new study.

The findings, led by Durham University, UK, could have implications for understanding how healthy eating habits might be established in babies during pregnancy.

Researchers analysed the facial expressions of babies who had been repeatedly exposed to either kale or carrot in the womb after birth.

Newborns whose mothers had taken carrot powder capsules when 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 kale scent.

The research included scientists from Aston University, UK, and the CNRS and University of Burgundy, France. It is published in the journal Appetite.

Research co-lead author and supervisor Professor Nadja Reissland, of the Fetal and Neonatal Research Lab, Department of Psychology, Durham University, said: "Our analysis of the babies' facial expressions suggests that they appear to react more favourably towards the smell of foods their mothers ate during the last months of pregnancy.

Potentially this means we could encourage babies to react more positively towards green vegetables, for example, by exposing them to these foods during pregnancy. In that respect, the memory of food the mother consumes during pregnancy appears to establish a preference for those smells and potentially could help to establish healthy eating habits at a young age."

 Nadja Reissland, Professor, Fetal and Neonatal Research Lab, Department of Psychology, Durham University

This study is a follow-up to a 2022 research paper where the researchers used 4D ultrasound scans at 32 and 36 gestational weeks to study fetal facial expressions after their pregnant mothers had ingested a single dose of either 400mg of carrot or kale capsules. Fetuses exposed to carrot showed more "laughter-face" responses while those exposed to kale showed more "cry-face" responses. 

For the latest study, the researchers followed up 32 babies from the original research paper – 16 males and 16 females – from 36 weeks gestation until approximately three weeks after birth.

Mothers consumed either carrot or kale capsules every day for three consecutive weeks until birth. When the babies were about three weeks old, the research team tested newborns' reactions to kale, carrot, and a control odour. 

Separate wet cotton swabs dipped in either carrot or kale powders, or water as the control, were held under each infant's nose and their reaction to the different smells was captured on video. The babies did not taste the swabs.

Scientists then analysed the footage to see how the newborns reacted and compared these reactions with those seen before the babies were born to understand the effects of repeated flavour exposure in the last trimester of pregnancy.

The research team found that, from the fetal to newborn period, there was an increase frequency in "laughter-face" responses and a decrease frequency in "cry-face" responses to the smell the babies had experienced before birth.

Humans experience flavour through a combination of taste and smell. In fetuses this happens through inhaling and swallowing the amniotic fluid in the womb.

Research co-lead author Dr Beyza Ustun-Elayan carried out the research while doing her PhD at Durham University.

Dr Ustun-Elayan, who is now based at the University of Cambridge, said: "Our research showed that fetuses can not only sense and distinguish different flavours in the womb but also start learning and establish memory for certain flavours if exposed to them repeatedly.

"This shows that the process of developing food preferences begins much earlier than we thought, right from the womb. By introducing these flavours early on, we might be able to shape healthier eating habits in children from the start."

The researchers stress that their findings are a baseline study only. They say that longer follow-up studies are needed to understand long-term impacts on child eating behaviour. They add that further research would also need to be carried out on a larger group of infants, at different points in time.

They say that the absence of a control group not exposed to specific flavours makes it challenging to fully disentangle developmental changes in the babies from the effects of repeated flavour exposure.

Future research should also factor in post-birth flavour experiences, such as some milk formulas known to have a bitter taste, which could impact babies' responses to the smell of bitter and non-bitter vegetables.

The research involved the children of white British mothers, and the researchers say that future studies should be widened to explore how different cultural dietary practices might influence fetal receptivity to a broader array of flavours.

Research co-author Professor Jackie Blissett, of Aston University, said: "These findings add to the weight of evidence that suggests that flavours of foods eaten by mothers during late pregnancy are learnt by the fetus, preparing them for the flavours they are likely to experience in postnatal life."

Research co-author Professor Benoist Schaal, National Centre for Scientific Research (CNRS)-University of Burgundy, France said: "Fetuses not only detect minute amounts of all types of flavours the mothers ingest, but they overtly react to them and remember them while in the womb and then after birth for quite long times.

"In this way mothers have an earlier than early teaching role, as the providers of the infant's first odour or flavour memories."