Asparagus Pee: Do You have the Gene Variant to Smell It?

Asparagus pee smell… something that I assumed everyone smelled. I mean, seriously, it is an inescapable, overwhelming, and unique smell. Right?

It turns out that many people reading this will have no idea what I’m talking about. But Benjamin Franklin knew (1781 quote), “a few stems of asparagus eaten, shall give our urine a disagreeable odour.”[ref]

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Asparagus Pee and Odor Receptors:

A question that has plagued scientists for a while is “what causes the odor in asparagus pee”. Research on the topic is still not set in stone.

When you eat asparagus, it is broken down and absorbed into the body. One of the metabolites produced from asparagus is “methanethiol,” which contains sulfur. Some consider it to smell a little like cooked cabbage.

Odor receptors are found on the surface of the cells lining the nose, and they lock with the different chemical molecules coming into the nose. Specific molecules dock with specific receptors, sending a signal through the olfactory nerve to the brain.

How common is it?

In a study of nearly 7000 participants, more than half of the people could not smell asparagus pee. The researchers asked the people if they could usually detect an odor after eating asparagus, and then they looked at genetic variants in the group.

Studying a smell like this is tricky, though. How much of the odor was present? Does it matter how the asparagus was cooked? At what concentration can it be detected? Can you smell it only in your own pee, or are you sniffing other people’s urine? (I’m not signing up for that study.)

Another study looked into whether it was a lack of ability to smell the odor vs. a lack of producing it. The study found that 8% of participants’ urine did not have a detectable asparagus odor. The researchers also found that the ability to smell the asparagus pee smell is much stronger in those who carry the A allele of rs4481887 (OR2M7 gene).