Why Does Asparagus Make Your Pee Smell

Eating asparagus with your dinner may sound like a good idea at the time, until you go pee that is. Unique in the fact that asparagus can create a weird yet distinct odor when you pee, the real question is why does asparagus make your pee smell?

What Is Asparagus?

Asparagus is a perennial vegetable, with a bright, earthy flavor which can be prepared in a variety of different ways. Asparagus is one of the most nutritionally balanced vegetables, rich with key nutrients and free of fat, sodium, and cholesterol.  

Asparagus Nutrition

Asparagus offers many health benefits with its unique plant compounds and key nutrients. One of the unique facts, in addition to the malodor it produces, is that it contains low levels of the amino acid asparagine, which acts as a diuretic [R]. Diuretics help rid the body of waste materials, excess salt and excess water, which can lower blood pressure and relieve stomach bloat.  Studies have also shown that asparagus may have anti-cancer benefits, since it contains the antioxidant glutathione. Glutathione is known for its detoxifying properties and may play a role in extinguishing carcinogens.

One 4 oz serving of asparagus contains

  • Calories: 13
  • Protein: 1.5g (3 percent daily value, or DV)
  • Fat: 0.1g
  • Carbohydrates: 2.6g
  • Fiber: 1.4g (5.6 percent DV)
  • Potassium: 135mg (2.9 percent DV)
  • Vitamin C: 3.8mg (6.3 percent DV)
  • Folate 35 micrograms (µg) (8.8 percent DV)
  • Vitamin A: 507 international unit (IU) (10.1 percent DV)
  • Vitamin K: 27.9 µg (34.9 percent DV)

Why Does Asparagus Make Your Pee Smell?

The sulphonic and unpleasant scent from eating asparagus when you pee is produced from the metabolism of asparagusic acid. When asparagus is digested, asparagusic acid is broken down into sulfur byproducts. And if you’ve ever smelt sulfur, you know there is nothing pleasant about it. It’s a real treat. When you pee these byproducts evaporate almost instantaneously, which enables them to travel to your nose so quickly.

Asparagus is metabolized quickly. The distinct order can show up within 15-30 minutes after eating asparagus and can last for several dreaded hours. Research indicates that the malodorous smell can last up to 14 hours [R].

That said, Asparagus does not make everyone’s pee smell, or at least some think they don’t.

One hypothesis, called the perception hypothesis, states that some individuals can’t recognize the smell associated with eating asparagus when they pee.

A study published in the BMJ polled a cohort of nearly 7,000 people and asked them to report if, “they noticed a strong characteristic odor in their urine, after eating asparagus.” Around 40% reported no significant changes of odor in urine, after ingesting asparagus.

The study concluded that a large proportion of people have asparagus anosmia. Anosmia, meaning the impairment of smell. Genetic variation near multiple olfactory receptor genes is associated with the ability of an individual to smell the metabolites of asparagus in urine. Therefore, this study suggests that 40% of individuals do not contain the genetic receptors to smell the odor created by asparagus when you pee [R].

Another hypothesis, the production hypothesis, suggests that some individuals are not capable of producing the sulfurous compounds responsible for the smell. Studies suggest that some people, around 8% lack a key enzyme responsible for metabolizing asparagusic acid [R].

Either way, just be hopeful that you fit into the 50-60% of people who are genetically gifted and don’t have the olfactory genes to smell it, or the key enzyme to produce it and break down asparagusic acid.

Why Does Asparagus Make Your Pee Smell: Takeaway

Despite the smell that can infiltrate your nose after eating asparagus, asparagus do have some key nutritional benefits worth considering. Asparagus is a great source of key nutrients like vitamin K, folate, and antioxidants. Studies suggest that asparagus can also aid in digestion, weight loss, and lower blood pressure. For those of us lucky enough to be gifted with asparagus pee, it may not be worth it. But for those that can’t smell it, or don’t produce the enzyme to break down asparagusic acid, have at it.


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