Eating asparagus can make your urine smell awful; find out why

Emeh Joy
By Emeh Joy

Basic medical scientist, health research writer with experience writing for health brands like Dentistry Brands LLC and KompleteCare.

Some people notice that after eating asparagus, their urine smells awful. Why is it so? What happens in the body that causes smelly pee after eating asparagus?

A woman perceiving a foul urine odour after eating asparagus

Sometimes people notice that after eating a particular food, their body reacts in a certain way. It could be that they feel nausea, bloated, pass too much gas, experience heartburn or have allergic reactions. 

One of the things you might notice with eating vegetables like asparagus (even though it is nutritious) is that it could cause you to pass smelly urine. 

Asparagus is a low-calorie vegetable that commonly grows in the temperate region. It is an excellent source of vitamins and minerals. 

This plant is commonly known to support fetal development. However, evidence-backed reports have shown that consuming asparagus can cause smelly urine. 

Why asparagus makes the urine smell

Asparagus causes pee to smell because the plant contains asparagusic acid, which is broken down into byproducts that contain sulfur.

“A few stems of asparagus eaten shall give our urine a disagreeable odour”, said Benjamin Franklin, author of "Fart Proudly: Writings of Benjamin You Never Read in School”.

When you eat asparagus, it gets digested, releasing an acid called asparagusic acid. Aspagursic acid is further broken down into byproducts that contain sulfur and ammonia.

Sulfur is known to have an unpleasant smell. So, when you urinate, the byproducts evaporate, making you perceive the unpleasant odour.

Some of the sulfur compounds that produce the characteristic urine odour include thiols and S-methyl thioesters

Why you should not stop eating asparagus

Photo by Travis Yewell on Unsplash

If the only problem with eating asparagus is that it makes your pee stink, then you should not stop eating asparagus.

Urine is the body’s natural way of disposing waste by filtering them out through the kidneys, and having the pee smell after eating asparagus is also normal. 

A 1987 British study found that about 43% of people experience a urine smell after eating asparagus.6 For those who don’t experience it, it could be because their body breaks down sulfur more efficiently, or they lack the ability to detect the odour because of their genetic makeup.5

A genetic mutation can alter olfactory perception, causing some people not to detect asparagus urine.

Studies have shown that asparagus contains more nutrients and fewer calories. It is an excellent food option for pregnant women as it contains folate (vitamin B9). Folate is necessary for a healthy pregnancy as it is required for DNA replication.1

Asparagus is also a good source of antioxidants. Antioxidants help to protect the body cells from oxidative stress, which induces chronic inflammation, diseases and ageing. 

Asparagus can improve your digestive health as it is a vegetable. Vegetables contain dietary fibre, which is good for gut health. Studies have also shown that fibre-rich foods may help reduce the risk of heart diseases, high blood pressure and diabetes. (4, 2)

Asparagus does not harm the kidneys; instead, it is a healthy diet that contains low potassium. People with kidney diseases are encouraged to consume diets that contain low potassium.

Other foods can change the smell of urine

Asides from asparagus, other foods can change the smell of your pee.  Such foods include:

  • Onions
  • Garlic
  • Brussels sprouts
  • Coffee
  • Fish
  • Cumin
  • Curry
  • Alcohol

Also, since urine is a combination of water and waste products, not drinking enough water (dehydration) can cause urine to smell. 

“When you are dehydrated, your urine has less water in relation to waste products, which can make you have smelly urine”, Dr Sonia Dutta, urogynecologist at NorthShore University HealthSystem in Illinois, said.3

What you can so your urine doesn't smell after eating asparagus

Photo by Simon Authur on Unsplash

Unfortunately, there is nothing much a person can do to prevent the distinct smell of urine after eating asparagus.

However, drinking cranberry juice and enough fluids may help counteract the effects and neutralise asparagus in urine. 

You may be lucky to have asparagus anosmia (inability to smell asparagus metabolite in urine) due to your DNA variation or difference in the way your body metabolises asparagus. Otherwise, you may have to deal with asparagus urine.

Fortunately, asparagus urine is not a big deal. The urine odour usually goes away within 24 to 48 hours; perceiving your urine odour for a short while is unpleasant, but it surely does not kill.  

See a doctor when necessary

When it comes to smelly urine, ingested foods are not the only possible culprits. Smelly urine is not something to ignore, especially if it persists or is accompanied by other symptoms.

Some medical conditions such as liver disease, yeast infection and urinary tract infection can cause foul-smelling urine.

If you still perceive the foul odour even after discontinuing the suspected food (such as asparagus), it will be best to see a doctor immediately.

References

  1. Greenberg, J. A., Bell, S. J., Guan, Y., & Yu, Y. H. (2011). Folic Acid Supplementation and Pregnancy: More Than Just Neural Tube Defect Prevention. Reviews in Obstetrics & Gynaecology, 4(2), 52–59. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3218540/
  2. InterAct Consortium (2015). Dietary Fibre and Incidence of Type 2 Diabetes In Eight European countries: the EPIC-InterAct Study and a Meta-analysis of Prospective Studies. Diabetologia, 58(7), 1394–1408. https://doi.org/10.1007/s00125-015-3585-9 
  3. Lauriello, Samantha. (2021). "9 Causes of Smelly Urine- and What To Do About It". Health. https://www.health.com/condition/digestive-health/smelly-urine-causes 
  4. Li, B., Li, F., Wang, L., & Zhang, D. (2016). Fruit and Vegetables Consumption and Risk of Hypertension: A Meta-Analysis. Journal of Clinical Hypertension (Greenwich, Conn.), 18(5), 468–476. https://doi.org/10.1111/jch.12777  
  5. Markt, S. C., Nuttall, E., Turman, C., Sinnott, J., Rimm, E. B., Ecsedy, E., Unger, R. H., Fall, K., Finn, S., Jensen, M. K., Rider, J. R., Kraft, P., & Mucci, L. A. (2016). Sniffing Out Significant "Pee Values": Genome-Wide Association Study of Asparagus Anosmia. BMJ (Clinical research ed.), 355, i6071. https://doi.org/10.1136/bmj.i6071 
  6. Mitchell, S. C., Waring, R. H., Land, D., & Thorpe, W. V. (1987). Odorous Urine Following Asparagus Ingestion In Man. Experientia, 43(4), 382–383. https://doi.org/10.1007/BF01940418 

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