Asparagus has been a popular delicacy for millennia, and for just as long, the end result of eating it—the distinct smell it gives one's urine—has captured the attention of people throughout the world. Benjamin Franklin wrote about it in 1781. Colombian author Gabriel García Márquez' described one of the characters from his 1985 novel Love In The Time Of Cholera as relishing "the immediate pleasure of smelling a secret garden in his urine that had been purified by lukewarm asparagus."
The powerful smell of the vegetable in our pee is caused by excreting methanethiol and S-methyl thioesters, metabolites (byproducts of digestion), from eating asparagus.
However, a portion of the population is physically incapable of knowing the poetic beauty of that very unique aroma—and scientists finally understand why.
In a recent study published in the British Medical Journal, researchers determined that from a pool of 6,909 participants, over 60 percent stated that they could not smell the odor caused by asparagus metabolites, a condition referred to as asparagus anosmia. Meanwhile, the remaining 40 percent strongly agreed that they smelled the aroma.
Scientists were able to determine that a single genetic variation affecting the sense of smell was likely the cause.
Sarah Markt, a research associate at the Harvard T.H. Chan School of Public Health, tells MUNCHIES, "Research has investigated specific anosmias as a key to understanding olfaction… Previous studies have found genetic variation associated with the ability to smell vanilla, cut grass, and sweat, for example."
While the study does seem to answer the fundamental question of what causes asparagus anosmia, Markt admits there's still much to learn about what factors would lead to that genetic change in the first place.
The next time the plate of those crowned, green stalks comes around, take a few extra and find out which part of the population you belong to—smellers or non-smellers.