Friday, June 17, 2011

Why Does Pee Smell After Eating Asparagus?

Peeing after eating asparagus can be daunting: The liquid takes on a strange, pungent, rotten odour which can be off-putting, to say the least. But why is that?

Asparagus contains asparagusic acid which is broken down into volatile (smelly) chemicals released in the urine as soon as half an hour after consuming the vegetable. These chemical components responsible for this effect are: methanthiol, dimethyl sulfide, dimethyl disulfide, bis(methylthio)methane, dimethyl sulfoxide and dimethyl sulfone.

The really fascinating fact is that some people do not produce smelly pee after consuming asparagus (though they're rare among the population), and some people still might produce it yet not be able to smell it as offensive! Scientists have not gone into the screws & bolts of how and why this is, but the most widespread explanation is genetic variations: Some people have genes that dictate their system to process asparagusic acid somewhat differently, while variation in the smelling perception spectrum is hypothesized to be a combination of genetic and societal factors coming into play.

pic of asparagus via


  1. What a weird and interesting post! I've always wondered the reason for this - thanks for solving the mystery!

  2. Ah ! I looooooove interesting facts like these!
    Sulfide, sulfone; all related to the odor of sulfure, an odor I like when I light a match :)
    Soooooo, i might think twice when I want to serve asparagus.
    Have a great weekend!

  3. I eat a lot of asparagus, so I'm very familiar. I don't find the smell offensive, just... asparagus-y. For some reason, this phenomenon brings out my inner eight year-old boy and I just giggle when it happens. I gotta say, I don't even think it takes a half hour for me - seriously, within minutes.

    Heh. Asparagus pee. Hee.

  4. It doesn't smell bad to me--just funny. Like StyleSpy--the smell makes me giggle!

    I'm also not completely averse to skunk scent. I suspect some sort of partial anosmia is to blame in both cases.

    The subject reminds me of the following quote, supposedly from a sign which hung in an old London gentlemen’s club lobby: “Members will kindly refrain from relieving themselves in the umbrella stand during asparagus season.”

  5. dleep16:27

    Count me as one of the people who don't notice an offensive smell after eating asparagus.

  6. Anonymous19:53

    and it's not just asparagus! there are other foods that give it different aromas! and hormones, too! so fun!

    meanwhile, fresh cat pee smells just that - fresh, and like hay! go figure.


  7. Eva S20:20

    I've never noticed any smell after eating asparagus (granted I don't eat it very often). But am I the only one who notice a distinct "coffee-smell" when I have to rush to the ladies half an hour after drinking huge amounts of morning coffee?
    Have a good weekend all!
    Eva S Sweden

  8. How appropriate, I ate some asparagus today. I think it ends up smelling like matches, thanks to the sulfur.

  9. Josephine,

    thanks, it's little things like that which tick the "mad scientist" in us, don't they. Glad you enjoyed!

  10. Violaine,

    LOL! The odour of actually lighting matches is rather pleasant to me, while the gases that would be ignited by it not so much.... On the other hand, sulphur in live volcanoes is quite pungent, like rotten eggs (have visited sites hence my mention). Asparagus wee is somewhere in the middle, I guess, on the scale!

  11. SS,

    you might be among the lucky ones who don't metabolise it with smelly after-effects or at least it's less intense? Such factoids do bring out the 8 year old, but that's not a bad thing!! :-P

  12. Amy,

    what an amazing phlegmatic (so British!) quote!! Absolutely love it, thank you!!

    Well, I know of a lot of people who rather like skank, you're not alone. I don't think it's anosmia, as much as cognitive process and association. First time smelling one being pleasant rather than unpleasant. Rachel Weisz seems to think the same way.

  13. Dleep,

    that's quite interesting! A live subject for the research! Thanks for the feedback.

  14. J,

    it's certainly some other foods too! I notice a subtle fish odour in the actual pee when I consume lots of fish in the summer. And too much coffee is especially noticeable in SO's wee on the occasions when he drinks a lot. (I'm cautiously entering the realm of TMI here...I'll stop)

  15. Eva,

    you're certainly not alone!! Read my comment above.

    I think everything in the system influences personal scent to a certain degree: it's fascinating.

  16. Elisa,

    serendipity or what? :-)

    It's an odd smell coming out of the bowl, but not really bad. (Then again "bad" to me is burning plastic)

  17. Love asparagus and eat plenty of it! AND it does not make my (you know what) smell!!! Lucky me.

  18. I'm in with Eva on the coffee-pee.

  19. I was a real picky eater when I was little, and the "stinky-pee" phenom is what my dad always used to try to entice me to eat asparagus when we had it once a year. I never would eat it (canned). He had the strangest ideas about what would get me to eat.

  20. TFC,

    I see you and cannot raise you one. Run out of luck on this one :-P

    Good on you! Asparagus is delicious!

  21. Woodgirl,

    coffee pee is far more common than generally admitted. I assume the kind of coffee consumed plays a role as well (it pays to take it Arabian and laced with cardamom, I guess!)

    Funny dad, weird technique and so very male!

  22. I'm sure that the first time I had a chance to stuff myself full with asparagus, I either didn't smell the asparagus piss or it didn't stink that way, I would have noticed because it was on my holiday in the Netherlands and I ate a kilo of it per day at least.
    No coffee or fish pee, as far as I'm aware.
    But, when we're playing 8 years old, I hear that red beet makes one's urine red.

  23. I've never made that connection, and I kept thinking there was something wrong with me!
    Now I'll have to check the next time I prepare and eat some. Love asparagus, and it's in season right now where I live. Thanks for this fascinating post, and solving a great mystery.

  24. Anonymous08:11

    İf ı say something wrong may God forgive me but should we eat asparagus? It was created for human alimentation? I dont really understand this snobish insistance to eat it. I was curious about it ı tried and already ı give up.
    Son there is no worry about the results after eat it....:)))

  25. L,

    odd! Beets do color things. Solid things (i.e. #2) too (one can get alarmed into thinking they have an hemorrhaging ulcer or something)

  26. OF,

    oh please, you're just human! :-) More or less we all have some reaction to it.
    I'n glad I solved a mystery for you.

  27. Anon,

    we're not *supposed* to eat anything in particular (and I doubt any plant grew originally for human alimentation) . It's just nice to some of us (fresh, crunchy, great with fresh butter melting on it).
    If it didn't suit you, that's OK. Plenty of other stuff to enjoy I guess. ΄-)

  28. Anonymous07:16

    Very interesting post. i will never look at asparagus in the same light again.


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