aspargus on a cutting board

Asparagus pee: Can you smell it?

Can you smell “asparagus pee” — the unmistakable odor some people can detect in urine after eating asparagus?

Less than half of people can, a study suggests… and whether you can or you can’t isn’t a matter of choice — it all depends on your  DNA.

aspargus on a cutting board

What’s that smell?

Asparagus is considered a delicacy, but it’s also known to produce a distinctive odor in urine. Not everyone can detect the odor of metabolites (methanethiol and S-methyl thioesters) produced by consumption of asparagus. Specifically, a large proportion of individuals of European-American descent cannot smell asparagus pee.

To learn more about who can smell asparagus pee and who can’t, Harvard Chan researchers surveyed 6,909 men and women of European-American descent participating in two long-term studies. They found that 58% of men and 62% of women were unable to smell the urinary metabolites produced after asparagus consumption. Those metabolites, the authors said, create “a rather malodorous bouquet.”

The researchers linked this data with a genome-wide association study measuring nine million inherited genetic variants, called SNPs (single nucleotide polymorphisms), in the participants.

Aspara-genetics

They found that 871 of the genetic variations were associated with the inability to smell asparagus pee — called, in technical terms, asparagus “anosmia.” All of the SNPs were located in a chromosomal region that contains multiple genes having to do with the sense of smell.

They also found that a higher proportion of women reported they were unable to detect the odor, compared to men, despite women being known to more accurately and consistently identify smells. The researchers suggest that this unexpected result might be due to under-reporting by a few modest women, or because they might be less likely to notice an unusual odor because of their position during urination.

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Study limitations include self reporting of odor, rather than an objective measurement, although this is unlikely to explain their findings, and the sample focusing on people of European descent, so it’s unknown whether the same genetic variants predict asparagus anosmia in other ethnicities.

The researchers said the discovery of these SNPs provides scientists with future research directions to uncover the genetic determinants of people’s overall sense of smell.



Pointing out the potential health benefits of eating asparagus — including a reduced risk of cancer, cognitive impairment, and cardiovascular-related diseases — the researchers urged people to eat the stalky vegetable, even if they are among those able to smell the disagreeable odor afterwards.

>> Get some asparagus recipes here

“Outstanding questions on this topic remain,” says senior author Lorelei Mucci, associate professor of epidemiology at Harvard Chan School. “First and foremost perhaps is: why such a delicious delicacy as asparagus results in such a pernicious odor, and what are the selective pressures driving genetic variations that lead to asparagus anosmia?”



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