I Thought Everyone Could Smell Asparagus Urine

In a recent paper called "Food Idiosyncrasies: Beetroot and Asparagus," Steve Mitchell of the Imperial College School of Medicine in London recounts decades of sometimes conflicting theories and research.

For instance, it wasn't until the 1950s that researchers concluded that not everyone produced the smell. So, for the first time, populations started getting divided into "excretors" and "non-excretors."

As Mitchell points out, it may have been "understandable" that it took so long to figure this out.

"Those who produce the odour assume, politely, that everyone does, and those who do not produce it have no idea of the olfactory consequences," says Mitchell. "There is no reason as to why these two opposing factions should converse on this subject."

Various studies over the last half-century have suggested that perhaps half of the people in Britain are excretors, while the figures for the United States are higher and one French study of more than 100 people found they were all malodorous after eating asparagus.

... [Scientists looked for a] component unique to asparagus that remained stable enough when cooked that it could then make its way to the digestive system more or less intact.

The answer — or at least the consensus after a half-century of research — is something scientists are calling "asparagusic acid."

That's the stuff that we, or some of us, turn into noxious fumes of sulphur.

You won't find asparagusic acid in anything else we eat, although its close relatives turn up in everything from tropical mangroves to marine worms.

Asparagusic acid, it turns out, is what young asparagus use to ward off parasites. As the plant ages, however, the concentrations decline...

Why doesn't everyone smell it?

"There might be some people who are odour-blind to it"

You learn something new every day.