Mums-to-be who find themselves craving popcorn, pretzels and crisps can be reassured that wanting salty foods is a normal part of pregnancy for all animals – even fruit flies.
Researchers looked at the changes in the brain during pregnancy which cause food cravings and how the brain knows what the body requires.
They were able to show salt-craving exists in flies much as it does in mammals, and that this craving plays an important role in their reproductive abilities.
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They were also able to identify the trigger for salt-craving and map several steps in the neural circuitry that brings about this change in behaviour.
Dr Carlos Ribeiro, of the Champalimaud Centre for the Unknown in Portugal, said: “Nutrition is a highly complex topic.
“To understand how the brain regulates nutrient intake, you need to work in an organism that gives you access to a lot of diverse technologies. In that respect, the fruit fly is unbeatable.
“We wanted to exploit these tools to uncover how the female fly’s food preferences changed after mating.
“Many mammalian species increase their preference for salt during pregnancy; but until now it was not known if the fruit fly shared this behaviour.”
The team found not only do flies share the women’s inclination towards salt during pregnancy, but also that higher salt levels in the diet result in higher production of offspring in flies.
Dr Ribeiro said: “We found that there is a direct correlation between the amount of salt in the diet and the amount of eggs they were able to produce.
“It seems that salt is important everywhere, from flies, to elephants, to humans. It also suggests the existence of unifying biological principles underlying this behaviour that could be traced across species.”
The researchers found salt craving was not based on the precise needs of the body of the female fly.
Dr Ribeiro said: “Even if their egg production was disabled, mated females showed increased salt preference, demonstrating that salt-craving was independent of the actual needs of the body.”
According to the results the female brain knows the body will need more salt to produce eggs and so it automatically changes the way it perceives salt to allow it to take in higher amounts.
The study also found the “tongue” of the flies becomes much more responsive to the taste of salt, leading to them preferring the taste, just like in humans.
The researchers looked at the biological mechanism which leads to the change in salt sensation in pregnant animals.
It was found male flies injects a molecule called Sex Peptide into the female which manipulates her taste perception.
PhD student Samuel Walker, said: “The molecule activates neurons in the uterus of the female.
“From there, we found that a short chain of neuronal interactions signals the brain to dial up the salt preference.”
Dr Ribeiro added: “Now we move on to the next question, which is to identify how the brain’s response to salt changes after mating to bring about this cross-species behaviour.
“We will continue using the fruit fly, an organism that is unbeatable in its array of genetic tools, which will be essential to understand a topic as complex as nutrition.”