Love it or loathe it, asparagus sometimes shows up on the dinner table. But there's a funny thing about this vegetable. Some people notice a distinct odor after eating asparagus while others seem oblivious to it. An AncestryDNA^® + Traits test can tell you if your DNA suggests you're able to detect the smell of asparagus metabolites in urine.

Why Does Asparagus Make Your Urine Smell?

Have you ever wondered, "Why does my pee smell after eating asparagus?" When your body digests asparagus, it produces a chemical called asparagusic acid. Asparagusic acid breaks down into sulfur-containing compounds, which are notoriously stinky (think rotten eggs). Some people can smell this in their urine after eating asparagus, but others can't.

Scientists used to think that asparagus caused some people to produce bad-smelling urine. However, it turns out that it's probably not the stench—but the ability to smell it—that varies. The inability to smell the effects of this vegetable is called "asparagus anosmia."

Passing on the "Asparagus Pee" Detection Gene

If you're wondering why you're able to detect "asparagus smell" in your urine, your genes have the answers. This is because non-genetic factors don’t play a significant role in this trait, so things like environment or diet aren't likely to affect whether you can or can’t smell this distinct odor.

The ability to detect this specific and distinctive smell appears to be a dominant trait. That means if you inherited the gene variant for smelling asparagus metabolites from either of your parents, you'll probably be more sensitive to the scent of smelly urine. It's also likely that variants in other olfactory genes may play a role, so there may be multiple genes involved in asparagus smell detection.

Science Behind the Asparagus Metabolite Detection Trait

An AncestryDNA Traits test looks at 205 genetic markers across your DNA to predict your ability to detect asparagus metabolites. One gene in particular that scientists think affects your ability to detect the asparagus urine smell is the OR2M7 gene on chromosome 1. The gene OR2M7 produces an olfactory receptor that allows you to pick up certain chemicals in the air, like sulfur or citrus. Small differences in your DNA around OR2M7 can leave you more or less able to detect the odors asparagus adds to your urine.

A study that included 6,909 people (of European-American descent) found that 61.5% of women and 58% of men had asparagus anosmia, so they couldn't smell asparagus in urine. While women usually have a better sense of smell, scientists don't know why this is different for asparagus metabolites.

Interesting Facts About Asparagus Urine Smell

If you can get past the distinctive post-consumption smell, you'll discover that this vegetable is a nutritious powerhouse. Half a cup of cooked asparagus only has 20 calories, but it has 2.2 grams of protein. That half a cup also provides you with 57% of your daily recommended intake of vitamin K and 34% folate. Plus, asparagus has vitamin C, fiber, and vitamin E.

An epidemiologist at Harvard University, Lorelei Mucci, points out that not being able to detect the scent of asparagus in urine can be useful since you'll be more likely to eat it without having to worry about odors in the bathroom later.

References

Block, Eric, Victor S. Batista, Hiroaki Matsunami, et al. "The Role of Metals in Mammalian Olfaction of Low Molecular Weight Organosulfur Compounds." Natural Product Reports. The Royal Society of Chemistry. May 10, 2017. https://pubs.rsc.org/en/content/articlelanding/2017/np/c7np00016b.

Chen, Angus. "We Unravel The Science Mysteries Of Asparagus Pee." NPR. December 14, 2016. https://www.npr.org/sections/thesalt/2016/12/14/505420193/we-unravel-the-science-mysteries-of-asparagus-pee.

Coyle, Daisy. "7 Reasons Why You Should Eat More Asparagus." Healthline. April 4, 2018. https://www.healthline.com/nutrition/asparagus-benefits.

Eriksson, Nicholas, J. Michael Macpherson, Joyce Y. Tung, et al. "Web-Based, Participant-Driven Studies Yield Novel Genetic Associations for Common Traits." PLOS Genetics. Public Library of Science. June 24, 2010. https://journals.plos.org/plosgenetics/article?id=10.1371%2Fjournal.pgen.1000993.

Feltman, Rachel. "New Study: Why Can Some People Smell Asparagus in Their Pee?" Popular Science. December 14, 2016. https://www.popsci.com/why-can-some-people-smell-asparagus-in-their-pee.

Markt, Sarah C., Elizabeth Nuttall, Constance Turman, et al. "Sniffing out Significant ‘Pee Values’: Genome Wide Association Study of Asparagus Anosmia." The BMJ. British Medical Journal Publishing Group, December 2016. http://doi.org/10.1136/bmj.i6071.

Mirsky, Steve. "Genes for Smelling Asparagus Metabolites Determine Urine Luck." Scientific American. March 1, 2017. https://www.scientificamerican.com/article/genes-for-smelling-asparagus-metabolites-determine-urine-luck/.

Mitchell, S. C., R. H. Waring, D. Land, et al. "Odorous urine following asparagus ingestion in man." Experientia 43, no. 4 (1987): 382-383. https://link.springer.com/article/10.1007/BF01940418.

Pelchat, Marcia Levin, Cathy Bykowski, Fujiko F Duke, et al. "Excretion and Perception of a Characteristic Odor in Urine after Asparagus Ingestion: A Psychophysical and Genetic Study." Chemical senses. Oxford University Press. January 2011. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3002398/.

Stromberg, Joseph. "Why Asparagus Makes Your Urine Smell." Smithsonian Magazine. May 3, 2013. https://www.smithsonianmag.com/science-nature/why-asparagus-makes-your-urine-smell-49961252/.

Theimer, Ernst Theo, and John E. Amoore. Fragrance Chemistry: The Science of the Sense of Smell. New York: Academic Press, 1982.