Asparagus Pee: Genes and Odor Detection

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

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?

It turns out that more than half of people were unable to smell asparagus pee in a study of nearly 7000 participants. 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).

 


Asparagus Pee Variant: Check your data

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OR2M7 gene: encodes an odor receptor

Check your genetic data for rs4481887 (23andMe v4, v5; AncestryDNA):

  • A/A: greater ability to smell asparagus pee[ref]
  • A/G: greater ability to smell asparagus pee
  • G/G: less likely to be able to smell asparagus pee

Members: Your genotype for rs4481887 is AG.

From the study on asparagus odor detection: “The A allele was associated with greater ability to detect the asparagus odorant, which is the same allele which was associated with this ability in a previous study.”[ref]

Keep in mind that while people with the A allele are better at detecting asparagus pee, the more common G/G genotype people can often detect the odor, especially at higher concentrations.

Other genetic variants are linked to being able to detect asparagus metabolites in other odor receptors. None of them are covered by 23andMe or AncestryDNA.

There are likely multiple odor molecules in ‘asparagus pee,’ and some people can detect different molecules at different levels.[ref]


Lifehacks:

There really isn’t much in the way of lifehacks here…

so instead, here is are a couple of asparagus recipes :-) Enjoy!

 

From Cafe Delites: Cheesy Garlic Roasted Asparagus recipe (a couple of other good asparagus recipes there as well!)

 

Recipe from the Spruce Eats website.

Related Genes and Topics:

Trimethylaminuria: Genetic variants that cause a malodorous body odor
Often referred to as ‘fish odor disease’, trimethylaminuria causes a strong odor in sweat, urine, and breath. It is caused by mutations in the FMO3 gene.ABCC11 gene:

Ear wax and no body odor
The ABCC11 gene determines both the type of earwax a person has and whether they have no armpit or body odor.

Key Genes to check for Alcoholism
Are there key genes to check for alcoholism? Learn more about the genetic connections to alcohol addiction and what research-backed treatment options are available.

Caffeine Metabolism and Your Genes
Caffeine remains the most popular ‘drug’ of choice for a large percentage of the population. Genetics determines how quickly your body processes and eliminates the caffeine and whether it is likely to make you jittery or anxious.

 

References:

“Cheesy Garlic Roasted Asparagus.” Cafe Delites, 22 Mar. 2020, https://cafedelites.com/cheesy-garlic-roasted-asparagus/.

Markt, Sarah C., et al. “Christmas 2016: Food for Thought: Sniffing out Significant ‘Pee Values’: Genome Wide Association Study of Asparagus Anosmia.” The BMJ, vol. 355, 2016. www.ncbi.nlm.nih.gov, https://doi.org/10.1136/bmj.i6071.

—. “Sniffing out Significant ‘Pee Values’: Genome Wide Association Study of Asparagus Anosmia.” BMJ (Clinical Research Ed.), vol. 355, Dec. 2016, p. i6071. PubMed, https://doi.org/10.1136/bmj.i6071.

—. “Sniffing out Significant ‘Pee Values’: Genome Wide Association Study of Asparagus Anosmia.” BMJ (Clinical Research Ed.), vol. 355, Dec. 2016, p. i6071. PubMed, https://doi.org/10.1136/bmj.i6071.

Pelchat, Marcia Levin, et al. “Excretion and Perception of a Characteristic Odor in Urine after Asparagus Ingestion: A Psychophysical and Genetic Study.” Chemical Senses, vol. 36, no. 1, Jan. 2011, pp. 9–17. PubMed Central, https://doi.org/10.1093/chemse/bjq081.

—. “Excretion and Perception of a Characteristic Odor in Urine after Asparagus Ingestion: A Psychophysical and Genetic Study.” Chemical Senses, vol. 36, no. 1, Jan. 2011, pp. 9–17. PubMed Central, https://doi.org/10.1093/chemse/bjq081.

—. “Excretion and Perception of a Characteristic Odor in Urine after Asparagus Ingestion: A Psychophysical and Genetic Study.” Chemical Senses, vol. 36, no. 1, Jan. 2011, p. 9. www.ncbi.nlm.nih.gov, https://doi.org/10.1093/chemse/bjq081.

“Try This Delicious Risotto Made With Fresh Asparagus.” The Spruce Eats, https://www.thespruceeats.com/asparagus-risotto-recipe-995994. Accessed 22 Nov. 2021.




Author Information:   Debbie Moon
Debbie Moon is the founder of Genetic Lifehacks. She holds a Master of Science in Biological Sciences from Clemson University and an undergraduate degree in engineering from Colorado School of Mines. Debbie is a science communicator who is passionate about explaining evidence-based health information. Her goal with Genetic Lifehacks is to bridge the gap between the research hidden in scientific journals and everyone's ability to use that information. To contact Debbie, visit the contact page.