People have been fascinated by this phenomenon of asparagus making your pee stink for eons.
Why, even Ben Franklin had something to say on the subject. He wrote, “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.” Turpentine? Well, anyway, back to asparagus.
As we were saying, it’s been a curious thing for quite some time. A researcher in the late nineteenth century actually thought he’d identified the substance that causes the stink: methanethiol.
He obtained these results by getting four men to agree to offer urine samples, then eat three pounds of asparagus each. After fifteen minutes or so, he had them urinate again, and when he compared the samples, he found that each of them suddenly contained larger quantities of methanethiol.
This was the standard explanation for years, until about 1975, when yet another researcher conducted similar tests. His results were a little different. He found that the odor derived from the compound S-methyl thioesters.
Neither explanation has been ruled out, and most sources list both possibilities instead of taking sides. Let’s just say that either one of these results can be summed up by stating that the stink occurs when the body produces sulfur compounds during the digestion of asparagus.
But your question is about why your urine doesn’t smell after eating asparagus.
Well, believe it or not, this too has been tested. Only about 22 percent of those polled claim to have smelly urine after eating asparagus. So why them, and not the rest of us? Well, when those same 22 percent were asked to smell the urine of the other 78 percent, guess what? They could smell the sulfur compounds at work.
The same was true in reverse: those 78 percent who claimed not to have stinky urine couldn’t smell a thing when asked about the smell of the other 22 percent.
So the answer is that your urine does smell when you’ve eaten asparagus, you just can’t smell it.