If the taste of sukuma wiki makes you scowl, you're not alone. Observational studies have found that foetuses grimace with a crying face when exposed to the bitterness of the leafy green vegetable.
The new study, which aimed at showing evidence of foetal reaction to different foods consumed by their mothers, also showed the foetuses seemingly smiling when their mothers ate carrots.
Published in Psychological Journal, the researchers found that flavours from the mother's diet, compounded of taste and smell, were present in amniotic fluid from 32 to 36 weeks gestation.
Scientists from the University of Durham used advanced 4D ultrasound scans to observe whether foetuses could react to different tastes. They found that the unborn babies made faces when exposed to different flavours in their mothers' diets.
About 20 minutes after the women swallowed the capsules, scans showed that foetuses exposed to carrot flavour responded with more facial expressions suggestive of smiling. In contrast, those exposed to kale flavour pressed their lips together in a grimace.
The ultrasound images showed facial movements similar to those of kids or adults upon tasting something bitter or sour, such as raising the upper lip or frowning with the lower lip. However, the researchers noted that it didn't mean the foetuses were expressing an early dislike for kale.
"We report the first direct evidence of human foetal responsiveness to flavours transferred via maternal consumption of a single-dose capsule by measuring frame-by-frame foetal facial movements," the study reads.
The study involved 100 pregnant women in the United Kingdom, and the foetuses were between 32 and 36 weeks gestation.
- We help breastfeeding mothers balance work and life
- There is more to nutrition than just 'food on the table'
- Kenya gets award for low maternal deaths
- On a mission to fight hidden hunger
Then, researchers gave 35 of the participating women capsules of powdered carrot, and 34 got capsules of powdered kale. Thirty women didn't consume either vegetable as a control.
The team chose to administer powdered vegetables to ensure that the flavours weren't diluted during digestion — and because many pregnant women couldn't handle the taste of kale juice, Nadja Reissland, a co-author of the study, told CNN.
The conclusion suggested that during the last three months of pregnancy, foetuses are mature enough to distinguish between different tastes of foods consumed by the mother, lead researcher Beyza Ustun told CNN.
"While the findings cannot prove that foetuses prefer carrots to leafy greens, the findings add to growing evidence that suggests babies begin developing their senses of taste and smell in utero, particularly in the third trimester," she said.
A follow-up study of the same babies post-birth is already underway, intending to determine whether prenatal exposure affects taste preferences later on, according to a press release from the University of Durham.
"We think this repeated exposure to flavours 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," said Utsun, a postgraduate researcher in the Foetal and Neonatal Research Lab at Durham.
Scientists believe that developing foetuses experience flavour by inhaling and swallowing amniotic fluid, which surrounds and nourishes them in the womb.
Past studies have documented how newborns respond to flavours introduced before birth in amniotic fluid or shortly after birth in breast milk. But while prior research has considered flavour preferences post-birth, the latest study is the first to capture how foetuses react to foods ingested by the mother while they are in the womb.