Early spring is a good time of year. Sci starts feeling a little more motivated, it’s finally warm enough to feel comfortable running outside again (not that Sci ran inside, she was just very uncomfortable outside), and it’s asparagus season!
When Sci was wee and her mother would try to feed her asparagus, Sci turned up her little nose at such nonsense. Why on earth would anyone eat something that was that green and looked like it had hair!?
I seem to remember as a child thinking that asparagus tasted over green and like unripe corn and I was very unimpressed. But as an adult I have come a real appreciation of this odd vegetable. You grill it up with some olive oil and spices on…yum. And so now I look eagerly for those little green bunches at the store.
And it was when I started eating asparagus that I heard about the pee thing.
So today’s Friday Weird Science is something that REALLY makes Sci curious. I mean, usually I just look for things that make me laugh. But now I’m on a quest, I want to KNOW!
It’s time for some weird and Historical (historical enough) science:
Most everybody knows that asparagus makes your pee smell funny. Some say it’s a high ammonia smell, some say it’s more like old socks, and some people…can’t smell it at all. What’s up with that? Since it’s now spring again and Sci is going on a real asparagus bender, she has had more than once wondered: what the heck is the chemical causing that smell?!
These guys set out to analyze what was in your urine following intake of asparagus that produces the weird smell. The researches here describe the smell as “rotten or boiling cabbage” but that doesn’t really seem right. Apparently, if people’s urine smelled after asparagus but BEFORE the introduction of fertilizer, nobody ever said anything about it or noticed it. So people thought that perhaps it was the sulfur compounds that have been used to improve the growth and flavor of asparagus, which get INTO the asparagus and make your pee smell funny. But the scientists in this paper point out several things:
1) The chemical(s) in charge must be volatile. They have to be able to get from the urine into the air to get to your nose. So just saying what’s in the urine isn’t going to explain the cause of the smell.
2) Previous studies to extract stuff in urine did things like boil it. That’s no good, chemicals that will come out with boiling AREN’T going to be present in urine at normal body temperatures
(unless you’re Dr. Manhattan, and I seriously doubt that guy has a problem with asparagus making his pee smell).
And so, the guys in this study took urine from people who ate asparagus (in this case, eight healthy guys and girls from the biochem department at the University of Birmingham, England). They had to make sure that all of them were capable of producing funny smelling pee after eating asparagus. They ALSO got a hold of some people (it happens in about 10% of the population) who DON’T produce the smell, and sampled them.
Anyway, they got these people, took a urine sample, and fed them asparagus for dinner. They then had them bring in their pee at time points from 0 to 24 hours later (I bet most of them were grad students).
They then separated out the urines and analyzed them for the components that were volatile at normal body temperature. To do this, they put the urine at wait level, and took GAS samples at head level, to get the area at which you’d smell the urine, to narrow it down to the right set of volatile compounds. They got these:
These were all compounds that weren’t there in the before sample, were there in the asparagus sample, and were ONLY there in the asparagus samples of those who could produce the smell.
They ALSO did something cool to check their work, they reconstituted the urine after they were done with it, and checked with dedicated “smellers” (people who they knew could smell this sort of thing) whether or not it still smelled. Interestingly, their panel of smellers could always tell the difference between two subjects, but not between each urine from a single subject. So each subject probably has varying amounts of each chemical in the urine.
So what’s so smelly about these compounds? You’ll notice they all (except one) contain the word “sulf” which means they contain sulfur. Methanethiol is known to be really smelly as well. The thing is, most of these compounds would probably be breathed out or broken down in the body after being ingested (when a compound is volatile enough to be a gas at body temperature, lots of things can happen to it). The authors hypothesize that probably the compounds lists above are not present in themselves in the asparagus, but are breakdown products that occur when the asparagus is being digested, which also explains why some people have a mutation that doesn’t produce the smell. For their candidate of what compound is responsible, they nominated the aptly named asparagusic acid. Preliminary studies from their laboratory (though this was 1987, and I don’t know that they ever published the further results), showed that this compound could be the right one. When asparagusic acid enters the body, it could be broken down, producing the compounds above, and making your urine smell!
Sci thinks this is pretty cool, as it’s something she’s always wanted to know. She also thinks it’s particularly funny that people, when they write about asparagus making your pee smell, go ON and ON about how SIGNIFICANT this is, that it’s a quality of LIFE issue! THINK of the HUMILIATION! The HORROR of having your date ruined when your girl finds out your pee SMELLS!!
Sci thinks that if your girl is finding this out on the first date, you’re doing it wrong.
Also, Sci thinks this experiment would be pretty cool to do in the lab! Apparently they just did this on a gas chromatograph with mass spec to determine the weights. Sci thinks that this therefore might be a REALLY cool experiment to conduct with an organic chem class in college. Have everyone eat asparagus and see who comes out smelling funny, with what compounds, and how much of each.
Finally, I have a question for you all. When you eat asparagus, what does the resulting urine odor smell like? The compounds would suggest a sulfurous odor (like being in a marsh), but Sci’s experience tells her otherwise. Anyone? And also, has anyone suffered quality of life issues from asparagus pee? Anyone?
Waring RH, Mitchell SC, & Fenwick GR (1987). The chemical nature of the urinary odour produced by man after asparagus ingestion. Xenobiotica; the fate of foreign compounds in biological systems, 17 (11), 1363-71 PMID: 3433805