Why does pee smell asparagus

Other people don't notice anything unusual after eating asparagus. There are two possible explanations for this: some people excrete smelly compounds in their urine after eating asparagus, while other people don't excrete them; or some people can smell the compounds, while other people can't.

Unfortunately, many of the papers on asparagus urine are short and lack detail. Allison and McWhirter were the first to report that there was polymorphism, using a chemical test for methanethiol and finding that 46 out of people were excretors. They did not say where there subjects where they were from presumably Britain or give any details about their chemical techniques.

In response to criticism Penrose of their study, Allison and McWhirter stated that methanethiol was clearly either present or absent; again, they gave no details about the chemical test they used. Lison et al took asparagus urine from a single individual and asked Israelis to smell different dilutions and find the lowest concentration that they could distinguish from tap water.

They found a lot of variation among individuals, then divided them into "smellers" and "non-smellers. Based on the second experiment, they concluded that everyone excretes the smelly substances, but there is variation in ability to smell them.

Hoffenberg took asparagus urine from a single individual and had 98 schoolchildren find the lowest concentration that they could distinguish from tap water. The distribution was somewhat bimodal, but as in Lison et al. Both Lison et al. Mitchell et al. Three smellers then smelled their asparagus urine and a control sample of normal urine and classified the urine samples as smelly or not.

All of the smellers agreed about the classification of all of the samples, which is a good indication that urine can be classified into two discrete types. Waring et al. This is further evidence that not everyone excretes the compounds. Richer et al. Unfortunately, they do not say how they assayed stinkiness. Erickson et al. Of course, it is unknown whether the people who hadn't noticed an odor were non-excretors or non-smellers. Pelchat et al.

They found that 3 out of 37 people produced asparagus urine that none of the other people could distinguish from normal urine, which means that some people really are non-excretors. Out of 31 people, 2 could not distinguish between the asparagus and normal urine of any of the subjects, meaning that there really are non-smellers. There was continuous variation in both excretion and smelling ability, as well; the asparagus urine of some people was easily detected by most of the people, while other people produced asparagus urine that only some people could detect.

Lison et al. Other papers using chemical tests and carefully controlled smelling tests show that there is variation in excretion of sulfur compounds in urine after eating asparagus. The lack of detail in some of the papers makes it difficult to be sure, but it may be that everyone, if fed enough asparagus, excretes enough stinky compounds that a careful sniff by a sensitive nose can distinguish the asparagus urine from non-asparagus urine. It may be that only some people excrete large enough amounts of stinky compounds to be noticably unusual.

Quantitative chemical analysis of sulfur compounds in the urine of a sample of asparagus eaters would be an obvious way to shed light on this. It is clear that in addition to variation in excretion, there is also variation in the ability to smell the compounds. It is not clear whether this variation is continuous, or whether people can be clearly divided into smellers and non-smellers. Testing the ability of people to smell different concentrations of the sulfur compounds that are hypothesized to be the cause of the odor, such as methanethiol and dimethyl sulfide, would help resolve this question.

Despite a number of studies, it is not entirely clear what compounds are responsible for the odor in asparagus urine. Nencki identified methanethiol a sulfur compound, also known as methyl mercaptan in asparagus urine, and Allison and McWhirter found that is was present in the urine of some asparagus eaters and absent in others' urine. White used gas chromatography on methylene chloride extracts of asparagus urine and identified S-methyl thioacrylate and S-methyl 3- methylthio thiopropionate; he suggested that these compounds would be easily broken down into methanethiol, thus explaining the earlier results.

He found that adding S-methyl thioacrylate and S-methyl 3- methylthio thiopropionate to normal urine made it smell like asparagus urine. They used gas chromatography of the vapor above urine, and they identified five compounds that were present in the asparagus urine vapor of five excretors but absent in the vapor of three non-excretors: methanethiol, dimethyl sulphide, dimethyl disulphide, dimethyl sulphoxide, and dimethyl sulphone.

And although thioesters can also grab your nostrils by the throat, they might have played a key role in the origin of life. So be glad they were there stinking up the abiotic Earth.

But does a compound reek if nobody is there to sniff it? Less philosophically, does it reek if you personally can't smell it? For only some of us are genetically gifted enough to fully appreciate the distinctive scents of postasparagus urine. The rest wander around unaware of their own olfactory offenses. Recently researchers dove deep into our DNA to determine, although we've all dealt it, exactly who smelt it. They don't bother to note that their bathroom humor plays on the ubiquity in research papers of the p -value, a statistical evaluation of the data that assesses whether said data look robust or are more likely the stuff that should never be allowed to mellow.

The findings appeared in the notorious Christmas issue, which always features screwball scholarship, of the BMJ known as the British Medical Journal from to —that is, two decades after Queen Victoria first sat on the throne until midway in the reign of Elizabeth II. Become an author Sign up as a reader Sign in. One of the signature fragrances of spring comes after the consumption of asparagus.

Sarah Coseo Markt , Harvard University. Ready for harvest. Scientists hope to use them in regenerative medicine. Learn more…. Ability to smell 'asparagus pee' driven by genetic variations. Written by Hannah Nichols on December 27, Share on Pinterest Recent research has identified the genetic origin of the ability to smell the odor in human urine produced after consuming asparagus.

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