Our bodies convert aspartic acid into sulfur-containing chemicals that stink … but some of us are spared from that nasty smell.
The characteristic smell that emanates from the bathroom after asparagus has been part of our menu may be familiar to many. However, not everyone is under the ordeal of “asparagus pee.”
Despite its known health benefits, asparagus is controversial. Whether green, purple, or white, its ability to turn some people back after visiting the bathroom has fascinated humans for centuries.
Since when is this peculiar smell talked about?
In fact, the first mention of the distinctive smell after consumption of asparagus dates back to the 11th century. As Stephen C. Mitchell, from the Imperial College London School of Medicine (UK), as stated in an article published in the journal Perspectives in Biology and Medicine : “ the ancients thought that asparagus had medicinal properties ” and took ” […] its odor-producing qualities as proof of its activity “.
But what causes the smell? And why does it cause that bad smell in some people, but not in others?
Asparagus pee and those that are not. What is not known is whether non-producers of asparagus pee actually secrete the smelly substances in their urine, but the levels are too low for our noses to detect.
At the heart of the question is the enigma of which chemical compound is to blame for the odor. The funny thing is that nobody really knows. Scientists believe that the odor in question is due to two chemicals: methanethiol and methyl sulfide thioester. When enzymes in the human digestive tract break down the aspartic acid that is naturally found in this vegetable, these volatile compounds are created. When they are expelled from the body, they turn into an unpleasant-smelling gas, which erupts in the form of what we have already called ‘asparagus pee’.
Mitchell explains that sulfur-containing chemical structures are often to blame for unpleasant odors. Rotten eggs are a good example of this.
Previous studies found the following compounds in urine after consuming a healthy dose of asparagus: methanethiol, dimethyl sulfide, and dimethyl disulfide. That said, the first two compounds were also detected in the air when the asparagus were boiled, indicating that cooking them could destroy them.
So the culprit is … aspartic acid
In his article, Mitchell points out that this compound is also known by its chemical description, 1,2-dithiolane-4-carboxylic acid. High levels of aspartic acid are believed to protect young asparagus shoots from parasites hungry for a tasty snack.
The chemical structure of asparric acid is highly resistant to degradation by cooking, leaving our intestines in charge of its decomposition.
Whether it is, in fact, aspartic acid, methanethiol, dimethyl sulfide, dimethyl disulfide, or some other compound … whatever the chemical base, the reason some of us consider the smell of asparagus to be offensive and others not, it is in our genes.
The key, in our genes
The asparagus pee story gets more complex here, as, in addition to producers and non-producers of asparagus pee, some people can smell asparagus pee, while others cannot.
These non-sniffers have asparagus anosmia , which is the technical term for the inability to smell. We just divided the world into four classes of people instead of two – asparagus pee, of course.
Thus, a recent study published in The BMJ identified changes in the genes responsible for smell, called olfactory receptor genes, between sniffers and non-sniffers. The study involved 6,909 men and women and showed that a whopping 60% had asparagus anosmia.
The question that remains to be answered is whether people with asparagus anosmia are more likely to eat asparagus than those who are subject to its smell. So remember that if you have never noticed the smell of asparagus on your pee, it is because you do not have the ability to detect it. Each person is a world of smells in himself.
Asparagus is not the only food that has curious effects linked to genetics. Some people avoid eating cilantro, for example, because they claim it has a “soapy” aftertaste.
What do you think?
Referencia: Asparagus, Urinary Odor, and 1,2-Dithiolane-4-Carboxylic Acid . Stephen C. Mitchell Perspectives in Biology and Medicine Johns Hopkins University Press Volume 56, Number 3, Summer 2013 pp. 341-351 DOI: 10.1353/pbm.2013.0031
