We know that pregnancy food cravings can include just about anything, but how do they get started? New research in mice identifies the part of the brain that seems to control these urges, which in future could help ensure that human pregnancies are as healthy as possible.
In tests on pregnant mice – who the team discovered also have cravings while expecting – researchers noticed changes in the reward circuits of the brain, as well as brain areas responsible for taste, and sensory and motor systems.
Within the mesolimbic pathway, responsible for delivering dopamine hits and rewarding the brain for its actions, the team identified higher levels of dopamine and increased activity from the dopamine receptor D2R in a region called the nucleus accumbens, part of the brain's reward system.
"This finding suggests that the pregnancy induces a full reorganization of the mesolimbic neural circuits through the D2R neurons," says neurobiologist Roberta Haddad-Tóvolli from the August Pi i Sunyer Biomedical Research Institute in Spain.
"These neuronal cells – and their alteration – would be responsible for the cravings, since food anxiety, typical during pregnancy, disappeared after blocking their activity."
While this study looks specifically at mice, the mouse brain and the human brain have enough in common for the scientists to consider whether the same sort of rewiring may be happening when human mothers are craving ice cream, chocolate, or whatever foodstuff it happens to be.
It's thought that cravings support embryonic growth in a variety of ways, but there are also potential problems – this eating of tasty, high-calorie foods has potential downsides for babies and their mothers.
The researchers went on to study the offspring of the mice that had been allowed to indulge their cravings for sweet foods, noticing differences in the metabolism and neural circuitry in this next generation.
"These results are shocking... [many of the previous studies in this area] are focused on the analysis of how the mother's permanent habits – such as obesity, malnutrition, or chronic stress – affect the health of the baby," says neurobiologist Marc Claret from the University of Barcelona in Spain.
"However, this study indicates that short but recurrent behaviors, such as cravings, are enough to increase the psychological and metabolic vulnerability of the offspring."
In follow-up tests on the mouse offspring, the researchers identified potential problems with weight gain, anxiety, and eating disorders. It remains to be seen how this would translate into human beings, but the signs aren't good.
The team behind this study is hoping that the research could help contribute to nutritional guidelines for expectant mothers, ensuring that even if food cravings are indulged every now and again, the overall diet remains healthy and good for both mother and baby.
With something like food cravings in pregnancy – where there is so much anecdotal evidence for what happens and why – it's important that there's also as much scientific investigation into the underlying causes as possible, say the researchers.
"There are many myths and popular beliefs regarding these cravings, although the neuronal mechanisms that cause them are not widely known," says Claret.
The research has been published in Nature Metabolism.