This raises the possibility there may be ethnic differences in the trait. Perhaps further clues might come from the chemicals that produce the signature smell. One prime suspect from many studies is a sulphur compound called methanethiol. In the study, though, the researchers found methanethiol present in the urine of some asparagus-eaters and not others. For that you need to examine the vapour given off by the urine. Analysis of the vapour using gas chromatography revealed four compounds.
The strongest smelling are methanethiol and dimethyl sulphide which smell like old cabbage. There are also two compounds which might give the odour that tinge of sweetness.
A thermogram of a man urinating into a toilet. Thermography records the temperature of objects by detecting long- wavelength radiation Science Photo Library.
These compounds are unlikely to have been in the asparagus when we ate it; they are small and delicate molecules that cooking would destroy. So what we need is a substance only found in asparagus, which remains intact during cooking, but is broken down by the body to produce the smaller odorous compounds.
Appropriately there is a substance unique to asparagus called asparagusic acid. Could this be the source of the smell? A nephrologist breaks down why the asparagus pee phenomenon happens.
Learn more about vaccine availability. Advertising Policy. You have successfully subscribed to our newsletter. Ever wonder why eating asparagus can lead to funky smelling pee? Related Articles. Feel Bloated? How to Follow a Diabetes-Friendly Diet. Trending Topics. Asparagusic acid is a sulfur-containing compound that seems to be found exclusively in asparagus. Asparagusic acid is a nontoxic, sulfur-containing compound that may cause your pee to have a distinct odor after eating asparagus.
Once your body metabolizes asparagusic acid, it produces several sulfurous byproducts that are highly volatile — meaning that they vaporize easily 3. When you pee, these compounds evaporate almost immediately, which enables them to travel from the urine up to your nose, allowing you to smell them. Some people notice the rotten-like smell as early as 15—30 minutes after eating asparagus, and studies have determined that within 25 minutes, half of the asparagusic acid consumed has already been absorbed 7.
The fast absorption rate suggests that the effect of asparagus on urine smell can appear quite quickly, and recent studies also agree that it can last for more than a few hours.
One study in 87 people who ate 3—9 spears of asparagus found that the half-life of the asparagus smell was 4—5 hours 3. The half-life of a substance tells you how long it takes for it to reduce to half of its initial amount.
Therefore, if the half-life of the asparagus smell was estimated at 4—5 hours, it means that the total effect could last up to 8—10 hours. Yet, another study in people who also consumed 3—9 asparagus spears reported the half-life of the smell to be 7 hours, meaning that the effect could even last up to 14 hours 7. When your body metabolizes asparagusic acid, it produces numerous smelly, sulfur-based compounds that give your pee a rotten-like smell that can last 8—14 hours. The effect of asparagus on urine scent is not universal, and a number of hypotheses try to explain this phenomenon.
One hypothesis — called the production hypothesis — suggests that only some individuals are capable of producing the sulfurous compounds responsible for the smell, while others are non-producers. This hypothesis asserts that non-producers lack a key enzyme that helps metabolize asparagusic acid and are thus unable to produce the smelly byproducts 4.
The other hypothesis — called the perception hypothesis — states that everyone produces the smell, but some are unable to detect or perceive it 4. In this case, researchers found a genetic modification that alters one or more of the olfactory receptors that should respond to the asparagus smell, causing what is known as asparagus anosmia, or the inability to smell asparagus pee 8.
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