The asparagus effect on making urine smell is something that have been puzzled people for centuries. Scottish physician John Arbuthnot wrote in 1731 that “asparagus affects the urine with a foetid smell”. French novelist Marcel Proust also tried to analyze why this specific vegetable “transforms my chamber-pot into a flask of perfume”. Even Benjamin Franklin himself commented on the fact in a 1781 letter he sent to the Royal Academy of Brussels: “A few Stems of Asparagus eaten, shall give our Urine a disagreable Odour”.
But why is that? Why does asparagus affects urine in such a way?
Well, modern science has finally given us the answer and as it turns out, it all comes down to one unique chemical that can only be found in asparagus: the asparagusic acid. (the article continues after the ad)
When we digest the vegetable, the asparagusic acid breaks down into different sulfur-containing compounds that ultimately convey an unpleasant yet powerful scent. This is pretty similar with other sulfur-containing substances such as the skunk spray and garlic. The fact with these other molecules is that they are volatile, meaning they have a low boiling point. This allows them to enter gaseous state at room temperature and travel right up your nose!
Contrary to that, asparagusic acid isn’t volatile and that’s why it doesn’t have that rotten smell. Once our body converts them into sulfur-bearing compounds though, their distinctive smell is generated rather quickly – just 15-30 minutes after consumption. And that’s why we notice the smell when we pee.