Asparagus and its' affect on the scent of urine
Tonight, I had a delicious serving of asparagus as a side dish to my dinner. Long into adulthood, I have retained the childish amusement I receive from the effect eating asparagus has on the scent of my urine. This is a phenomenon that affects subset of all people, most sources I have read estimate less than 50% of people are genetically predisposed to digest asparagus in the way necessary to alter the scent of one's urine. Even further, it has been noted that not all people have the genetic ability to detect the odor! So even if you are one of the few and proud who produce asparagus scented urine, you may not be aware of it. (I wonder if this also explains why certain people don't know they stink...)
Being a Chicagoan, I have been a fan of the Cecil Adams' column, The Straight Dope, for many years. Those familiar with The Straight Dope will not be surprised that this topic was discussed in a Straight Dope column many years ago. I include Cecil's answer at the end of this post but if you are not familiar with his column you should check out his website to discover well researched answers to all of life's obscure questions but be sure to put your learnin' hat on because Cecil's been "fighting ignorance since 1973".
There is a more recent post on the topic over on Discovery.com. The author contradicts some of Cecil's information but the she does admit she is speculating for various reason mentioned. Can't we just re-run the gas chromatography-mass spectrometry experiment for crying out loud? Surely there are some grad students with too much time on there hands somewhere.
Lastly, there is an entry in the British Journal of Medicine that asserts that all individuals create the odor but only a portion of individuals actually posses the ability to detect it. And that this phenomenon has lead people to suppose they do not create asparagus scented urine.
...oh, sweet lord I need a life.
From Cecil Adams "The Straight Dope"
[Why does asparagus make your urine smell?]
I have probably been asked this question a dozen times since I started this job. The first ten times I dealt with it as you might expect. I burned the letter, had the room fumigated, and prayed for the writer's immortal soul.
This week, however, I have gotten the question twice in the same mail. This leads me to believe this is something the Teeming Millions truly yearn to know, God help us. So I give up. Here's the story:
Many sagacious persons have noted the peculiar effect of certain products on human urine.
For example, Benjamin Franklin, in a wide-ranging discussion of bodily discharges, once noted, "a few stems of asparagus eaten shall give our urine a disagreeable odor; and a pill of turpentine no bigger than a pea shall bestow upon it the pleasing smell of violets."
It is said that in a venerable British men's club there is a sign reading "DURING THE ASPARAGUS SEASON MEMBERS ARE REQUESTED NOT TO RELIEVE THEMSELVES IN THE HATSTAND."
Serious scientific research in this field dates back to 1891, when M. Nencki tentatively identified a compound known as methanethiol as the culprit. The odor appears within an hour after eating just a few spears of the offending vegetable.
According to Allison and McWhirter (1956), the ability to produce the odor is controlled by a single autosomal (i.e., non-sex-related) dominant gene. In a sample of 115 persons, 46 were rendered fragrant by asparagus and 63 were not. (This leaves 6 mysteriously unaccounted for. Urology is an inexact science, I guess.)
In 1975 one Robert H. White, then with the chemistry department at the University of California at San Diego, found that the odor-causing chemical was not methanethiol after all.
Instead, using gas chromatography-mass spectrometry (Bob was obviously not one to screw around), he found that the aroma was in fact caused by several S-methyl thioesters, specifically S-methyl thioacrylate and S-methyl 3-(methylthio)thiopropionate.
(Thioesters are compounds that result from the reaction of an acid with a sulfur-containing alcohol. They tend to be smelly.)
I know you are very interested in all this stuff and are following me closely, F., so I am going to give you the exact chemical formulation for these chemicals, in case somebody asks you at some fancy social soiree.
The thioacrylate recipe is:
CH2=CHC(=O)SCH3
The thiopropionate is:
CH3SCH2CH2C(=O)SCH3
We are faking the above somewhat given the limitations of the ASCII character set, but I know you are grateful for whatever information we can provide.
Anyway, sez Bob, the "metabolic origin [of the compounds--i.e., how and why they end up in the urine] remains an open question." I can't exactly say that research is continuing, but if anything develops I'll let you know.
--CECIL ADAMS
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