Why Asparagus Makes Your Pee Stink (Even If You Think It Doesn’t)

To pee or not to pee—asparagus-urine, that is.

We’re going to try not to get too TMI here, but we love asparagus. We eat as much of the lovely green herald of springtime as we can. And, well, we’ve always wondered: Why does it give our urine that peculiar asparagus-pee smell? Even more curiously, why doesn’t it affect the urine of other members of our family? We’d always heard that detecting this warm-weather harbinger was somehow genetically coded. Now comes a more detailed explanation from one of our favorite websites, mentalfloss.com. (If you don’t follow it on Twitter, you’re missing lots of fun!)

Back in 1891, a guy named Marceli Nencki got some other guys to chomp down on three and a half pounds of green stalks apiece and figured out the culprit in asparagus’s afterlife was methanethiol; later research implicated the (imaginatively named) asparagusic acid. Asparagusic acid contains sulfur. Sulfur stinks—so much so that ancients considered hell to be filled with it in the form of brimstone, the old-fashioned name for sulfur. Volcanoes spew brimstone, so it was considered an agent of divine pissed-offedness.

But we digress. When humans ingest asparagusic acid, their pee acquires that distinctive odor. Or, rather, the pee of 20 to 40 percent of them does. The rest of us/them don’t, and will swear that their piss don’t smell. Except! When those who can detect the asparagus-pee smell smell the pee of those who say they are asparagus-pee-free, they can smell asparagus pee! In other words—asparagus makes ALL our pee smell. It’s just that the majority of us have an anosmia—an inability to smell a particular smell—so we don’t know it does.

And that, we suspect, is more than you ever wanted to know about aspargusic acid, not to mention what our mother used to call “not a proper topic for dinner-table discussion.” Unless, of course, you’re serving asparagus.

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