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Sparagrass eaten to excess sharpens the humours, and heat a little; and therefore persons of a bilious constitution ought to use them moderately: They cause a filthy and disagreeable smell in the urine, as every body knows.
-Louis Lémery, 1704
Although it appears to be a widely known fact that asparagus affects the chemistry of urine, how and to what extent has been debated. Some people claim they can’t smell the difference, while others claim it simply doesn’t affect them at all! There must be an explanation for the variation. In fact, there have been a surprising number of studies on the subject.
An Israeli study, in the 1980s, found that among 307 subjects, all of them had been affected by asparagus. 10% of those volunteers were not able to smell the difference, but the others were able to smell it in all sample. This study, and two others from France and Chine, would suggest that all humans are affected, but a study in 2010 revealed that some people are not!
That same year, 23andme did a genetic study on the subject. They are in a unique position to do a study because of their massive collection of genetic data. They simply asked their users if they noticed a different smell in their pee after eating asparagus. This pinpointed the exact gene that allows for people to detect the smell.
While the discovery doesn’t explain everything, it does show that there are genetic differences in the way that we detect smells.
Cello Concerto in E minor, Op. 85 by Edward Elgar, performed by the Skidmore College Orchestra