What’s Asparagusic Acid?
Asparagusic acid is a non-toxic sulfur-containing compound found exclusively in asparagus.
This acid gives pee a stinky smell after eating asparagus.
Why Does Asparagus Make Your Pee Smell?
When asparagus is digested, asparagusic acid is broken down into volatile (they vaporize easily) sulfur-containing by-products, which are released into pee.
When you pee, these volatile compounds evaporate instantly into the surrounding air, allowing your nose to smell them.
Common odor-causing by-products include methanethiol, dimethyl sulfide, dimethyl sulfone, and trimethyl trisulfide.
Methanethiol (methyl mercaptan) is the most common odourant found in the urine after eating asparagus.
How Long Does The Smell Last?
Studies have stated that a stinky pee smell usually appears 15 to 30 minutes after eating asparagus and can last for several hours, sometimes up to 14 hours.
Does Asparagus Make Everyone's Pee Stink?
It is natural to wonder if something is wrong with you when your pee stinks due to asparagus. However, asparagus pee stink is normal.
There may be two reasons why asparagus may not make everyone’s pee stink.
- Since everyone digests food differently, they break down sulfur differently to produce varying by-products
- Some people may not be able to detect the odor due to genetic variations
People cannot detect the unpleasant asparagus metabolites in their pee and are also unable to diagnose it in the urine of other individuals.
Asparagus anosmia is the inability to smell the asparagus metabolites in the urine.
How Do Genes Influence Asparagus Pee Smell?
Genetic variations are said to influence the ability to smell asparagus in urine.
Researchers have found that the ability to detect this odor is stronger in people who carry the A allele of rs4481887 in the OR2M7 gene.
This gene produces an olfactory receptor that interacts with certain molecules in the nose to produce the perception of smell.
| Genotype | Interpretation |
| AA | Greater inability to detect asparagus pee odor |
| AG | Normal inability to detect asparagus pee odor |
| GG | Less likely to detect asparagus pee odor |
Why Are Some People Unable To Detect This Smell?
Several hypotheses are stated for why some people cannot detect the pee odor. These include
- Production hypothesis: This theory suggests that some people can produce sulfur by-products responsible for the stinky pee smell while others are non-producers.
These individuals are said to lack a key enzyme that metabolizes asparagus acid to give stinky by-products.
So, they can either not produce the smell or produce it in small concentrations too low to be detected.
- Perception hypothesis: This theory states that everyone produces a stinky asparagus pee smell, but some cannot detect or perceive it.
This is said to be due to genetic changes that alter one or more olfactory receptors that respond to the smell of asparagus, giving rise to asparagus anosmia.
Apart from these reasons, how an individual eats asparagus also influences their ability to detect the smell of sulfur compounds.
The inability to detect asparagus pee odor is also more common among women than men, but this may be due to their position while urinating.
Summary
- Asparagus contains a non-toxic, sulfur-containing compound called asparagusic acid that gives a stinky pee on eating this vegetable.
- The asparagusic acid in asparagus is metabolized into volatile compounds that give rise to the characteristic stinky pee.
- The stinky pee smell usually appears 15 to 30 minutes after eating asparagus and can last for as long as 14 hours.
- Asparagus stinky pee smell is normal; around 20% to 50% of people experience it since they digest the vegetable differently.
- Genetic variations influence an individual’s ability to smell the asparagus stinky pee smell.
- People having the A allele of rs4481887 in the ORM2 gene have a greater ability to smell the stinky asparagus pee smell than those having the G allele.
References
- https://www.webmd.com/a-to-z-guides/ss/slideshow-things-that-can-affect-the-smell-of-pee
- https://health.clevelandclinic.org/why-does-asparagus-make-your-pee-smell/
- https://www.healthline.com/nutrition/why-does-asparagus-make-your-pee-smell
- https://www.news-medical.net/health/Genetics-of-Asparagus-Smell-in-Urine.aspx
- https://www.medicalnewstoday.com/articles/314722
