What You Learned About How Asparagus Works Was Probably Wrong

It’s a small quirk of human metabolism that Asparagus makes our urine smell. Due to some research in the 80s we’re now pretty darn sure that the smell is caused by a triage of sulfur containing alkyl compounds citation. But a few decades before scientists pulled out the big guns and nailed down exactly what was causing this phenomenon, they looked at the much simpler question: “Who makes smelly urine?” Observations of the day held that many people met tales of Asparagus Urine with vacant stares, and a few studies revealed that the percentage of people making smelly urine was in the low 40s citation . (This study was done in The UK and would probably yield very different results in other countries.)

So the scientists concluded, this is a polymorphism, different phenotypes existing in the same population. Some people’s digestive tracks produce the malodorous compounds, and some don’t. Simple enough right? I’ve been told they even managed to find the corresponding genotypes, and the correlation they had was great. I heard it got as far as children’s textbooks, before someone pointed out a tiny flaw in the experiment.

The experimenters had been a bit shy in their work. They’d fed people asparagus and asked: “Now does your pee smell?” when they should have asked the more risque: “Does his pee smell?” Had they asked the latter they would have found that ≈40% of people said yes all the time, and  ≈60% said no all the time. Because it turns out that everyone digests asparagus the same way and outputs the same urine, it’s just that not everyone can smell it.

…transforms my chamber-pot into a flask of perfume -Marcel Proust

This post was inspired by an old Daniel Miessler post which surfaced yesterday on Hacker News entitled “ Why Planes Fly: What They Taught You In School Was Wrong .”

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  1. You have a spelling error in the second sentence of your last paragraph. You wrote, “Had they asked the later they would have found… (sic)”. It should be “Had they asked the *latter* they would have found…” instead.

  2. Thanks, all fixed now.