An Investigation of Asparagus Pee

It has been noticed for centuries -if not longer- that eating asparagus gives one’s urine a distinctive smell. Describing the smell is a problem, though. Some people (Proust) liked it, others didn’t (Ben Franklin), while some have never encountered the smell. Those who recognize it just call it “asparagus pee smell.” And there’s some difference in our knowledge as to whether everyone produces the smell after eating the vegetable, and whether everyone has the ability to detect it, particularly since smelling urine is a subject many people just don’t talk about.

One thing most scientists agree on: asparagusic acid (which, as its name suggests, is only found in asparagus) is metabolized into sulfur-containing compounds, like methanethiol—the most prominent smell in your asparagus pee. These chemicals usually have a low boiling point, becoming smelly gases at room temperature, and hitting us in the face with that familiar odor.
But who makes asparagus pee, and who smells it?
According to Professor John H. McDonald in the biology department at University of Delaware, a 1980 study found that all participants produced asparagus pee, but only some smelled it. A 1987 study found the opposite; only some participants produced asparagus pee, but everyone could smell the difference. And a 1989 study found that 103 French people all produced asparagus pee and all of them identified it as stinky.

Then there are the people who aren’t sure which category they fall in, because they don’t like asparagus and don’t prepare it for the family. Read more about the effects of asparagus on urine at First We Feast.