Hello and happy Saturday! Here’s this week’s round-up of eclectic and under-the-radar health and medical science news.
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Searching for the sixth sense of taste
“Scientists identify a sixth taste sense.” It’s a claim that has made headlines several times over the last few years — first for fat, then for starch and even for water. Now the new candidate for the sixth taste is calcium, after scientists identified the first calcium taste receptors in fruit flies.
Researchers at the University of California studied fruit fly behaviour and discovered the flies could taste toxic levels of calcium and didn’t like it. Then they used genetics to show that the calcium taste sense is hardwired into the fruit fly brain.
And because fruit flies and humans share the other main taste senses — sweet, sour, bitter, salty and savoury (called “umami”) — the study’s lead author, Craig Montell, thinks there’s a good chance that humans also have specific calcium taste receptors.
“I would say there is very good reason that, given that all the other tastes have been well conserved between flies and humans, that there probably is,” said Montell.
But the science of taste is surprisingly complicated. Even the idea that there might be additional taste receptors is controversial. As far back as Aristotle’s time, scientists have been puzzling over the question.
“Since people have been doing scientific research on taste there’s been this disagreement over whether there are these fundamental or basic tastes,” said neurobiologist Gary Beauchamp, who is an expert in the science of taste and has been researching the question for years at the Monell Chemical Senses Center in Philadelphia.
The controversy revolves around the definition of “taste sense.”
“By that I mean something that is perceptually distinct and very clear,” Beauchamp said. As a test, he considers whether other cultures have also identified the taste.
“There’s no doubt that things like calcium, starch, fat interact with our taste system and modulate what we like and what we consume,” Beauchamp said. “But to me, calling this a sixth taste is nonsense, as far as humans go.”
Umami — commonly associated with savoury flavours including cheese, cooked meat and monosodium glutamate (MSG) — is the most recent addition to the list of human taste senses, but it was only officially accepted after scientists began discovering humans had specific receptors.
“To call something an actual type of taste requires not only seeing there’s a behavioural taste. But to show that it’s really innate, it’s helpful to be able to identify a receptor,” Montell said.
“There’s really still a lot of questions. Even for sour tastes there isn’t a receptor that’s been reported yet. The ones that have been really well characterized in humans are sweet, bitter and umami. Sodium has been a little bit more enigmatic.”
Both scientists agree that taste science matters.
“There’s a very important goal in understanding how taste works,” Beauchamp said. But despite the fruit fly findings, Beauchamp dismisses calcium as a distinct human taste sense.
“The discovery of a receptor for calcium in fruit flies is very interesting,” he said, but for humans it’s already covered by the five existing senses.
“You would just call this another bitter taste.”
Should we care what fruit flies can taste? Yes, Montell said.
That’s because the fruit fly has been a reliable model for understanding human physiology. Also, understanding what fruit flies and mosquitoes taste, can help fight human disease by identifying new methods of insect control.
“Insects, like mosquitoes that spread diseases like…