Why does asparagus make your pee smell funny?
Dear Cecil:
My faith in you remains unshaken and my respect for the sagacity of your judgment undiminished. However, I am afraid that, as Mitzi Malone might say, your interlocutors have gotten pretty weenie.
What you need are some good questions, such as the following: Why does my urine smell funny after I've eaten asparagus?
Dear F.:
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.
