Skinny On

Why Asparagus Makes Your Pee Stink

Why Asparagus Makes Your Pee 

by Hannah Holmes

"This is of no practical importance," the urologist tells me. "It wasn't part of my training. It's something we contemplated over pizza and beer." When I admit that I have actually timed the arrival of the distinctive odor in my pee after eating asparagus (about 15 minutes), the good doctor suggests, facetiously, that my groundbreaking research might lead to a tenure-track position at a fine university.

It is a sadly neglected field. But I'm not the first to ask.

In 1891 a scientist named "Nencki" had so very little to do that he convinced four guys to eat seven kilograms of asparagus (that's about three and a half pounds each). He collected the pertinent pee, worked some medieval magic on it, and concluded that the smell was due to a metabolite called methanethiol.

So there you go. Nencki claimed that as your body metabolizes asparagus, it produces this smelly chemical, which your discriminating kidneys see fit to dump into the bladder.
This probably doesn't qualify as red-hot science, but it's warm enough to spark differing opinions.

In 1975 a chemist from California claimed in Science that gas chromatography had fingered a different culprit: S-Methyl Thioesters, to be precise. No methanethiol.

Then there's the 1980 reference in the British Medical Journal that simply refers to "metabolites." Another asparagus scholar favors "six sulfur-containing compounds."

I'm voting for methanethiol, partly because the guy who did the gas chromatography left no forwarding address, and partly because the methanethiol entry in my aging Merck Index of chemicals is so interesting.

Methanethiol is composed mostly of sulfur with a splash of hydrogen, plus some carbon, a brew famous for its effect in rotten eggs, cabbages and paper mills. Convincing, no? Merck also notes the asparagus connection and, most intriguing, warns that methanethiol may be a narcotic in high concentrations.
Now if you're scowling at your screen and muttering, "My pee doesn't smell like asparagus," first ask yourself if you eat asparagus.

Even if you do but lack the smell, you're still OK. In fact the fabulously funny book, The ReSearch Guide to Body Fluids (by Paul Spinrad, Juno Books, N.Y., 1994), says just 22 percent of survey respondents experience asparagus pee.

Early investigators thought genetics had divided the world into stinkers and nonstinkers. That was until 1980, when three researchers had the presence of mind to wave pee from the nonstinkers under the noses of the stinkers.

Lo and behold, the problem proved to be one not of producing the stinky pee but of being able to sniff it out.

If you've been deprived of this gift, don't give up hope. To increase the concentration of methanethiol molecules available to your snoot, you could either intentionally dehydrate yourself before you dine (this is unhealthful); or pee into a cup and sniff that. Or eat three and a half pounds of asparagus for lunch.

And if you experience a narcotic effect, you could be looking at a tenure-track position at a fine university.

Asparagus fleet, n. Roman emperors were so fond of asparagus, which probably originated near the Mediterranean, that they kept special boats for the purpose of fetching it.

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Hannah Holmes sniffs out answers to life's oddities in Portland, Maine. She's a regular contributor to Discovery Channel Online and also writes for Escape, Outside, Sierra, Backpacker, Eco Traveler and Women's Sports and Fitness. Write her at

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Illustration: Brian Frick
Copyright © 1997 Discovery Communications, Inc.