In his novel "Love in the Time of Cholera," Gabriel García Márquez describes the very bad day of Dr. Juvenal Urbino. His friend has committed suicide, his pet parrot is stuck in a tree, and the firemen summoned to rescue it have trashed his house — and in the fracas, his bird escaped. Urbino's only consolation in the midst of these disasters? A nap, and the "immediate pleasure of smelling a secret garden in his urine that had been purified by lukewarm asparagus."
To each his own, as they say.
If you're not one yourself, you've probably heard about these people — the ones who can smell asparagus in their pee. A new study published in the British Medical Journal pinpoints the genes likely responsible for the ability to smell the compounds found in our urine after we've eaten asparagus. And they didn't just find one gene variant, but hundreds of them across multiple genes. What the study doesn't address is why asparagus, of all foods, makes our urine stink, and why our bodies have obviously put so much effort into being able to detect metabolized asparagus in pee.
Past research going back to the 1950s has shown that some people produce asparagus-scented urine, and some don't, and some people can smell it, and some can't. And some of that previous research identified the two metabolites responsible for The Odor, but nobody had investigated whether the ability to smell these two compounds, called methanethiol and S-methyl thioesters, was written on our genes.
The research team, led by Sarah Markt and Lorelei Mucci at the Harvard T.H. Chan School of Public Health, found that of the 6,909 study participants (both men and women, all of European-American descent) about 40 percent of them could smell these metabolites in their urine after eating asparagus, and 60 percent could not — these people they termed "asparagus anosmic." After looking at 9 million genetic variants in those who were asparagus anosmic, they linked this deficiency to 871 individual sequence variations they discovered in chromosome 1, on genes associated with our sense of smell.
Strangely enough, even though women are known for being super smellers, able to correctly and consistently identify smells more often than men, fewer women reported being able to smell their own asparagus pee. Because the study relied on the participants correctly reporting their experience, the researchers aren't sure whether some of the women lied about the smell of their urine out of modesty, or perhaps it was just hard to smell because of the position they were in when they produced the urine in question.
The researchers concede that the study has limitations. For instance, it focused entirely on people of European descent, so there's no telling whether the same genetic variants would be found in people of other ethnicities. Also, the participants self-reported the odor, which always leaves a little wiggle room for interpretation. And subjects only reported on the smell of their own urine, rather than whether they could smell asparagus in the urine of other people, though a 1980 Israeli study previously took that approach.
But don't worry if you can't smell the asparagus on your pee — these researchers have your back:
"Future replication studies are necessary before considering targeted therapies to help anosmic people discover what they are missing," the research team writes in the report.