The sweet taste of heavy water

Having only the very subtle substitution of hydrogen with its heavier, naturally occurring isotope deuterium, heavy water, D2O, has only a minor effect on the chemical properties of water. In principle, it should have no effect on the neutral taste of water. Here, using sensory evaluation techniques, we demonstrate that humans are, nevertheless, able to distinguish D2O from H2O by taste. Indeed, highly purified heavy water has a distinctly sweeter taste compared to same-purity normal water. To elucidate if the sweet taste of heavy water is mediated through the T1R2/T1R3 sweet taste receptor, we test the effect of lactisole (known as T1R2/T1R3 inhibitor) on D2O sweetness using a combination of tasting experiments. Lactisole decreases the response of sweetness in D2O. Moreover, exploring D2O in-vitro, we also show that exposure to D2O increases indeed significantly the IP1 levels in transfected but not in non-transfected HEK293T cells. This study suggests a potential activation of the human T1R2/T1R3 sweet taste receptor in the sweet perception of heavy water and opens path to better understanding of the molecular origins of sweet taste perception of certain non-carbohydrate substances.