Not everyone loves asparagus, although the right melted cheese sauce certainly makes for a tasty dish. What's not so pleasant is the smell of your pee after you eat it. Asparagus pee doesn't happen to everyone, but it happens enough to make people wonder why does asparagus make your pee smell? The short answer is that it's a result of asparagusic acid being metabolized.
Asparagusic Acid? What's That?
This acid is a compound that contains sulfur. While it's not the only compound to contain sulfur, it does seem to be something you only will ever find in asparagus. It's not toxic, but it does produce a rather sulfurous odor. If you think it smells like rotten cabbage, then you're far from alone. Many things that contain sulfur, including skunk spray, natural gas, and rotten eggs, have a strong, pungent smell. This is why researchers think that asparagusic acid is what makes your pee smell funky after you eat the veggie.
How Does That Impact the Scent of Urine?
When your body metabolizes any asparagusic acid you consume, the result is a number of sulfurous byproducts with high volatility. In this case, high volatility doesn't mean explosiveness or anything, just that they will vaporize easily and quickly. These compounds will evaporate nearly instantly when you pee. That lets them travel through the air quickly from your urine and rise up to your nose. That's when you unfortunately smell them. Researchers have yet to figure out if one particular compound is the solitary culprit behind the smell or if it takes a mixture of many of them. However, studies looking into it seem to highlight one particular compound called methanethiol. It's also known as methyl mercaptan. No matter what name it's called, it's usually a strong and seriously unpleasant scent. It happens a lot with bad breath and fecal odor.
How Long Will It Linger
Some people who eat asparagus notice this rotting smell in just 15 minutes to half an hour. Research has shown that half of consumed asparagusic acid is absorbed by the body in only 25 minutes. This is a rather fast rate of absorption and would seem to show that asparagus can impact the scent of urine rather quickly. Unfortunately, the impact can also last several hours. One study conducted involved 87 people. They each eat anywhere from three to nine asparagus spears. The results determined that asparagus smell in their urine had a half-life of approximately 4.5 hours. Since a half-life of something is the time it takes for it to be reduced down to half of its original amount, that actually means the overall impact of asparagus on urine can last nearly nine hours. Making matters worse was another study involving 139 people. That study's reported half-life was 7 hours, implying a potential half-life of 14 hours.
Not Everyone Is Affected
Asparagus pee doesn't happen to everyone. People are curious about this, but to date, there are multiple hypotheses as to why it might happen. The production hypothesis is one possibility. It suggests that only certain people are physically capable of producing those sulfurous compounds blamed for the smell. Everyone else would be a non-producer. The thinking is that non-producers don't have a particular enzyme used for metabolizing asparagusic acid, meaning there are no smelly byproducts when they next visit the bathroom. One small study of 38 adults ascertained that roughly 8 percent of them produced concentrations too insignificant to smell or just didn't produce the smell at all.
Another hypothesis is the perception hypothesis. It claims that everyone can produce the smell, but certain people just can smell it. Researchers are aware of a specific genetic modification that can alter one or several olfactory receptors known to respond to the smell of asparagus. A lack of this response is a condition called asparagus anosmia, which is the inability of a person's nose to smell their asparagus pee. Research backs up the perception hypothesis. One study, involving nearly 7,000 adults, demonstrated that over half of men and women had confirmed cases of asparagus anosmia. This implies that the genetic modification in question is rather common among the populace.
If you've ever heard someone talk about asparagus pee and wondered what it was, then you should know it's a strong and rather unpleasant scent from your pee after you eat this vegetable. The cause of it is probably certain compounds found only in asparagus that get quickly absorbed and metabolized in such a way that they can evaporate immediately during urination and float up to your nose. Fortunately, not everyone has to suffer through this. Over half of adults seem to lack the nose genetics required to even smell it, and it's possible that not everyone even produces asparagus pee. Those that do might have to live with it all day or night, though.