For many people, the fact that asparagus makes urine have a foul smell is a well-known fact. For many others, this effect does not seem to exist.

Researchers have finally come up with an answer about why this happens. It seems that a combination of 871 small genetic variations may actually prevent certain people from detecting the unpleasant odor in their urine after eating asparagus.

A Well-Known Fact ... For Some

That urine gives off an unpleasant smell after the consumption of asparagus has been known for a long time. Even Benjamin Franklin wrote about the phenomenon, being very convinced that everyone was aware of the effect. The truth however is that most people actually do not seem to be able to sense any difference at all.

A team of researchers decided this is a mystery worth investigating and as a result conducted a study on 6,909 American-European subjects with the aim of identifying the causes of the phenomenon.

The participants were told to eat asparagus and then evaluate the smell of their urine, and 2,748 or 39.8 percent of them said that they were able to detect a very unpleasant smell.

At the same time, 4,161 or 60.3 percent of the participants were not able to detect any distinct odor in their urine, and so were considered to be asparagus anosmic. For these people, the entire phenomenon is quite mysterious, especially as the descriptions of the smell can be quite varied, ranging from "cabbage-like" to "skunkish."

Having established who can smell the distinct odor of asparagus pee and who cannot, the scientists wanted to find out whether anosmic people were in any way different genetically.

Although the exact gene for the difference was not discovered, 871 single nucleotide polymorphisms may be behind this phenomenon. The scientists identified them after having analyzed 9 million genetic variations.

All the variations are found on chromosome 1, which is indeed correlated with certain olfactory receptors. At this point, scientists do not know what the exact implications of the discovery are, so they continue their research in order to find out more about the human ability - or inability - to smell.

Asparagus And Its Properties

While conducting the research, scientists were concerned that the results may prevent certain people from eating asparagus, which is not a desirable result.

"Asparagus is rich in iron, fiber, zinc, folate and vitamins A, E and C. Consumption of asparagus, as part of a diet high in vegetables, has been hypothesized to reduce the risk of cancer, cognitive impairment, and cardiovascular related diseases," they wrote.

This study was published in the Christmas edition of The BMJ, which tackles some rather light-hearted subjects that are perfectly sound from a scientific point of view. Another study published in the same journal shows that Pokémon GO players do get to exercise more, but only for about six weeks.