Fetuses smile at carrots but grimace at kale, study suggests


While it is known that some children are not big fans of greens, a new study suggests that such dietary preferences may come before they are even born.

Fetuses make more of a “laugh face” in the womb when exposed to the taste of carrots consumed by their mother and make more of a “cry face” response when exposed to kale, according to a study published in the journal Psychological Science on Wednesday.

“We decided to do this study to understand more about fetal abilities to taste and smell in the womb,” said lead researcher Beyza Ustun, a postgraduate researcher in the fetal and neonatal research lab at Durham University in the United States Kingdom, CNN told Thursday via email.

While some studies have suggested that babies can taste and smell in the womb using post-birth outcomes, “our research is the first to show direct evidence of fetal responses to tastes in the womb,” Ustun added.

“The findings show that fetuses in the last 3 months of pregnancy are skilled enough to distinguish different flavors that have been transferred from the maternal diet.”

The study looked at the healthy fetuses of 100 women aged between 18 and 40 who were between 32 and 36 weeks pregnant in the North East of England.

Of these, 35 women were placed in an experimental group that consumed an organic kale capsule, 35 were placed in a group that took a carrot capsule, and 30 were placed in a control group that was not exposed to either taste

Participants were asked not to consume food or flavored beverages for one hour before their scans. The mothers also did not eat or drink anything with carrot or kale on the day of their scans to ensure that it would not affect the results.

While carrot flavor may be described as “sweet” by adults, kale was chosen because it conveys more bitterness to infants than other green vegetables such as spinach, broccoli or asparagus, according to the study.

After a waiting period of 20 minutes after consumption, the women underwent 4D ultrasound scans, which were compared with 2D images of the fetuses.

The pulling of the corner of the lips, suggestive of a smile or laughter, was significantly higher in the carrot group compared to the kale and control group. While movements such as lifting the upper lips, lowering the lower lip, pressing the lips, and a combination of these – suggesting a crying face – were much more frequent in the cabbage group than the other groups.

“Nowadays we all know the importance of (a) healthy diet for children. There are many healthy vegetables, unfortunately with (a) bitter taste, which is usually not attractive to children,” said Ustun. She added that the study suggests “we can change their preferences for such foods before they are even born by manipulating a mother’s diet during pregnancy.

“We know that having a healthy diet during pregnancy is crucial for the health of children. And our evidence can be useful to understand that adjusting the diet of the mother can promote healthy eating habits for children,” added she.

Advances in technology have allowed for better images of the faces of fetuses in the womb, according to Professor Nadja Reissland, head of the fetal and neonatal research lab at Durham University. Reissland, who supervised the research, developed the Fetal Observable Movement System (FMOS), with which the 4D ultrasound scans were coded.

“As technology advances, the ultrasound image becomes better and more accurate,” she told CNN, adding that this “allows us to encode fetal facial movements frame by frame in detail and over time.”

The researchers have now started a follow-up study with the same babies after birth to see if the flavors they experienced in the womb affect their acceptance of different foods in childhood, according to the press release.

All the women who participated in the study were White and British.

“Further research should be conducted with pregnant women who come from different cultural backgrounds,” Ustun told CNN. “For example, I come from Turkey and in my culture we like bitter food. It would be very interesting to see how Turkish babies react to bitter taste.”

She added that “genetic differences in terms of taste sensitivity (being a supertaster or non-taster) may have an effect on fetal responses to bitter and non-bitter tastes.”