Laughter-face reaction scan image

Laughter-face reaction scan image. (Credit: Durham University/Aston University)

BIRMINGHAM, England — It seems that becoming a fussy eater starts before birth. Eating carrots during pregnancy makes babies happy in the womb, according to a new British study. The nutritious root vegetable causes developing fetuses to seemingly “laugh” or smile, while the more bitter leafy green kale, on the other hand, has the opposite effect — turning the smiles to scowls.

It appears that expecting moms can change the mood of unborn infants by what they have for breakfast, lunch and dinner. Their food choices could influence the taste buds of children as they grow up, with implications for obesity, researchers say.

Scientists recorded the first direct evidence unborn infants react differently to various smells and tastes by looking at their facial expressions. An analysis of 4D ultrasound scans show how they responded after being exposed to flavors from foods eaten by 100 pregnant women.

“A number of studies have suggested babies can taste and smell in the womb, but they are based on post-birth outcomes while our study is the first to see these reactions prior to birth,” says lead author Beyza Ustun, a PhD student at Durham University, in a statement. “As a result, we think this repeated exposure to flavors before birth could help to establish food preferences post-birth, which could be important when thinking about messaging around healthy eating and the potential for avoiding ‘food-fussiness’ when weaning. It was really amazing to see unborn babies’ reaction to kale or carrot flavours during the scans and share those moments with their parents.”

Fetus "scowls" at kale
4D ultrasound of a baby reacting to the flavor of kale. (Credit: Durham University/Aston University)

The international team studied how the fetuses behaved just a short time after ingestion by the mothers. Those exposed to carrot or kale showed more “laughter-face” or “cry-face” responses, explains Ustun. The findings published in the journal Psychological Science sheds fresh light on the development of human taste and smell receptors. What pregnant women eat might also influence babies’ preferences after birth, and help establish an appetite for fruit and vegetables.

Humans experience flavor through a combination of taste and smell. In fetuses, this may happen through inhaling and swallowing the amniotic fluid that surrounds a developing baby.

“Previous research conducted in my lab has suggested 4D ultrasound scans are a way of monitoring foetal reactions to understand how they respond to maternal health behaviours such as smoking, and their mental health including stress, depression and anxiety,” explains co-author Nadja Reissland, also from Durham. “This latest study could have important implications for understanding the earliest evidence for foetal abilities to sense and discriminate different flavours and smells from the foods ingested by their mothers.”

The mothers, aged 18 to 40, were scanned after 32 and 36 weeks of pregnancy. They were given a single capsule containing about 400mg of carrot or kale powder around 20 minutes before. It was all they consumed for at least an hour. The women also did not eat or drink anything else containing carrot or kale that day.

Facial reactions showed exposure to just a small amount of carrot or kale was enough to stimulate a reaction, compared with control fetuses not exposed to either.

“Looking at foetuses’ facial reactions we can assume a range of chemical stimuli pass through maternal diet into the fetal environment,” notes co-author Benoist Schaal, of the University of Burgundy in France. “This could have important implications for our understanding of the development of our taste and smell receptors, and related perception and memory.”

The phenomenon might also help with information given to mothers about the importance of taste and healthy diets during pregnancy. The researchers have now begun a follow-up study with the same babies post-birth to see if the influence of flavours they experienced in the womb affects their acceptance of different foods.

“It could be argued repeated prenatal flavour exposures may lead to preferences for those flavours experienced postnatally,” adds co-author Jackie Blissett, of Aston University. “In other words, exposing the fetus to less ‘liked’ flavours, such as kale, might mean they get used to those flavors in the womb. The next step is to examine whether foetuses show less ‘negative’ responses to these flavours over time, resulting in greater acceptance of those flavours when babies first taste them outside of the womb.”

South West News Service writer Mark Waghorn contributed to this report.

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