If the taste of kale makes you scrunch up your face, you’re not alone: Scientists have observed that fetuses pull a weepy expression when exposed to the green in the womb.
While previous studies have suggested that our food preferences may begin before birth and can be influenced by the mother’s diet, the team says the new research is the first to look directly at unborn babies’ response to different flavors.
“[Previously researchers] just looked at what happens after birth compared to what does [offspring] prefer, but actually seeing facial expressions on the fetus when they are hit by the bitter or by the non-bitter taste, that is something that is completely new,” says Prof Nadja Reissland from Durham University, co-author of the research.
Writing in the journal Psychological Science, the team noticed that aromas from the mother’s diet were present in the amniotic fluid. Taste buds can detect taste-related chemicals from 14 weeks of pregnancy, and smell molecules can be sensed from 24 weeks of pregnancy.
To delve into whether fetuses distinguish specific flavors, the team looked at ultrasound scans from almost 70 pregnant women aged 18 to 40 from the north-east of England, who were split into two groups. One group was asked to take a capsule of powdered kale 20 minutes before an ultrasound scan, and the other was asked to take a capsule of powdered carrot. The mothers’ vegetable consumption did not differ between the kale and carrot groups.
The team also examined scans from 30 women, taken from an archive, who did not receive any capsules.
All women were asked not to eat anything else in the hour before their scans.
The team then performed a frame-by-frame analysis of the frequency of a host of different facial movements in the fetuses, including combinations that resembled laughing or crying.
Overall, the researchers examined 180 scans from 99 fetuses, scanned at either 32 weeks, 36 weeks, or both.
Among the results, the team found that fetuses showed a crying expression about twice as often when the mother consumed a kale capsule compared to a carrot capsule or no capsule. However, when the mother ingested a carrot capsule, the fetuses adopted a laughing-like expression about twice as often as they did when either a kale capsule or no capsule was swallowed by the mother.
Dr. Benoist Schaal, an author of the work, from the Center for Taste and Feeding Behavior at the University of Burgundy, told the Guardian that the clarity of the results was surprising.
“[They mean] the mother has not yet finished her meal [when] the fetus is already aware, or able to sense, what the mother has eaten,” he said.
Beyza Ustun, first author of the research, said the team is now looking to explore babies’ response to the different flavors after birth. “Hopefully, if they were exposed to kale prenatally, we would see fewer adverse reactions,” she said.
Reissland added that the study could also offer a useful way to talk to pregnant women about what they eat. “What [we] In fact, other research shows that if the mother has a varied diet, such as vegetables and fruits, etc., babies are much less picky, she says.
Dr. Julie Mennella, an expert in the field from the Monell Chemical Senses Center in the US, who was not involved in the study, noted that the research supported previous work showing that offspring begin to learn about the mother’s diet through food tastes present in amniotic fluid.
But she cautioned that the pregnant women were not randomized to experimental or control groups, and that prior exposure of the fetuses in the control group to various vegetables — including carrots and kale — was not known.
Professor Catherine Forestell, from the College of William & Mary, said the work provided a window into the chemosensory world of the human foetus.
“Future work highlighting individual differences in fetal responses to taste and how they relate to maternal dietary habits and infant responses to foods after birth will be of great interest,” Forestell added.