An anonymous reader quotes a report from ScienceAlert: [T]here’s been a longstanding question over whether heavy water tastes the same as regular drinking water — or whether its subtle isotopic variation yields a different taste that people may be able to perceive. “There is anecdotal evidence from the 1930s that the taste of pure D2O is distinct from the neutral one of pure H2O, being described mostly as ‘sweet,'” an international team of researchers led by first authors and biochemists Natalie Ben Abu and Philip E. Mason explains in a new study. [I]n their new research, Ben Abu, Mason, and their team can finally confirm that there really is something a bit different about the taste of heavy water. “Despite the fact that the two isotopes are nominally chemically identical, we have shown conclusively that humans can distinguish by taste (which is based on chemical sensing) between H2O and D2O, with the latter having a distinct sweet taste,” explains senior author and physical chemist Pavel Jungwirth from the Czech Academy of Sciences.
In a taste-testing experiment with 28 participants, most people were able to distinguish between H2O and D2O, and tests with mixed amounts of the waters revealed that greater proportions of heavy water were perceived as tasting sweeter. In tests with mice, however, the animals did not seem to prefer drinking heavy water over regular water, although they did show a preference for sugared water — suggesting that in mice, D2O does not elicit the same sweet taste that people can perceive. Other taste tests conducted by the team suggest why this is so, indicating that human taste receptivity to D2O is mediated by the taste receptor TAS1R2/TAS1R3, which is known to respond to sweetness in both natural sugars and artificial sweeteners. Experiments in the lab with HEK 293 cells confirmed the same thing, showing robust responses in TAS1R2/TAS1R3 expressing cells when exposed to D2O. The findings are published in the journal Communications Biology.