The “Asparagus Effect” is Not Universal
By Kyle Kurpinski
Have you ever noticed a peculiar odor from your urine after eating asparagus? If so, you’re not alone. The “asparagus effect” has been documented since at least the 1700’s and was scientifically analyzed as early as 1891 when a chemist named Marceli Nencki attributed the smell to the chemical “methanethiol.” Most people would probably be satisfied with this explanation and move on, but science leaves no stone unturned; we now know that the distinct aroma is actually due to an intricate combination of sulfur-containing compounds (including methanethiol) formed during the breakdown of asparagusic acid.
So, mystery solved, right? Not quite.
Ask around, and you will find that only a portion of the population actually experiences the asparagus effect. A few early studies in the 1980’s reported that not everyone could smell the asparagus-induced odor, but those who could smelled it in all available samples, suggesting that everyone produces the aroma after eating asparagus, but only a portion of the population has the ability to detect it; a characteristic that was subsequently linked to a specific mutation in a group of olfactory genes. However, a more recent study in 2010 reported that a small percentage of people may not produce the odor at all, likely due to differences in the way they metabolize asparagusic acid.
In short, if you don’t notice the odor in your pee after an asparagus-heavy meal, you either have a unique, asparagus-proof metabolism or you simply lack the smell receptors to perceive your own stinkiness. If you do experience the asparagus effect, keep in mind that the odor-inducing precursor compounds are more prevalent in younger plants, so the smell will be less pronounced if you eat asparagus that is a little more mature. The effect is also extremely rapid – producing smelly pee in as little as 15-30 min after ingesting – so plan ahead if you’re thinking about eating asparagus on a hot date.
Image: Jonathan Moreau (cc)