Why Eating Asparagus Makes Your Pee Stink

Asparagus stalks on white surface

Verywell / Alexandra Shytsman

Some people notice their urine has a distinctive odor after eating asparagus. Often described as sulfurous or similar to cooked cabbage, the scent is due to the body's reaction to natural compounds found in the green stalks.

If you've never eaten asparagus or are unfamiliar with the "asparagus pee" phenomenon, smelling that odor for the first time could be quite alarming. However, it is normal, though not all people experience it.

In fact, a 2016 study found that roughly 60 percent of people of the (roughly) 2600 people studied didn't notice a strong characteristic odor in their urine after eating asparagus.

According to research published in the journal Chemical Senses in 2011, the reason you may or may not recognize eau d'asparagus is two-fold. Some people are unable to smell it, while other people do not seem to have a reaction to asparagus.

In both studies, researchers used DNA data to identify which genes, if any are responsible for the phenomenon, and came up with roughly 800 different possibilities.

What Is Responsible for Smelly Asparagus Pee?

For more than a century, scientists have sought to determine the precise chemical compound responsible for asparagus pee.

Methanethiol was the first one to be blamed in 1891. Since then, many other compounds have been proposed as the possible stinkers—variations of sulfides, methanes, and butyl found in the vegetable.

The latest culprit appears to be 1,2-dithiolane-4-carboxylic acid, better known as asparagusic acid.

An otherwise harmless compound, asparagusic acid is found only in asparagus. It was identified as the major chemical precursor to the smell in a research review published in Perspectives in Biology and Medicine in 2013.

Further studies show that in 4.7 hours, half of the asparagusic acid has been metabolized.

Is the Smell a New Phenomenon?

Asparagus has been around for thousands of years, but one of the first mentions of eau d' asparagus appeared in literature in the mid 1500s when botantist and physician Pietro Andrea Mattioli decribed multiple times the "stinking"odor that asparagus produced in urine.

Benjamin Franklin also mentioned the asparagus-pee connection in his essay, "Fart Proudly," a paper urging scientists of the day to develop a method to change the offensive odor of expelled gas. He used asparagus as an example of how the various things that go into the body can affect the odors that come out of it.

Many people describe asparagus pee as sulfur-like, so it's interesting to note that sulfur-containing fertilizers were first used to improve the flavor of asparagus late in the 17th century, and descriptions of asparagus pee began to appear shortly after that.

Asparagus Cooking Methods

There is no research to suggest that the manner in which asparagus is prepared has any impact on urine smell. Asparagus can be enjoyed raw, boiled, broiled, sautéed, or grilled.

Unsure how to prepare asparagus? Try these recipes:

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  1. Markt SC, Nuttall E, Turman C, et al. Sniffing out significant "pee values": genome-wide association study of asparagus anosmia. BMJ. 2016;355:i6071. doi:10.1136/bmj.i6071

  2. Pelchat ML, Bykowski C, Duke FF, Reed DR. Excretion and perception of a characteristic odor in urine after asparagus ingestion: a psychophysical and genetic study. Chem Senses. 2011;36(1):9-17. doi:10.1093/chemse/bjq081

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