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Why Does Asparagus Make Your Pee Smell Funny?

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The asparagus has a long and storied history. It was mentioned in the myths and the scholarly writings of ancient Greece, and its cultivation was the subject of a detailed lesson in Cato the Elder's treatise, On Agriculture. But it wasn't until the turn of the 18th century that discussion of the link between asparagus and odorous urine emerged. In 1731, John Arbuthnot, physician to Queen Anne, noted in a book about food that asparagus "affects the urine with a foetid smell...and therefore have been suspected by some physicians as not friendly to the kidneys." Benjamin Franklin also noticed that eating asparagus "shall give our urine a disagreeable odor."

Since then, there has been debate over what is responsible for the stinky pee phenomenon. Marceli Nencki identified a compound called methanethiol as the cause in 1891 after a study that involved four men eating about three and a half pounds of asparagus each. In 1975, Robert H. White, a chemist at the University of California at San Diego, used gas chromatography to pin down several compounds known as S-Methyl Thioesters as the culprits. Other researchers have blamed various "sulfur-containing compounds" and, simply, "metabolites."

More recently, a study demonstrated that asparagusic acid taken orally by subjects known to produce stinky asparagus pee produced odorous urine, which contained the same volatile compounds found in their asparagus-induced odorous urine. Other subjects, who normally didn't experience asparagus-induced odorous urine, likewise were spared stinky pee after taking asparagusic acid.

The researchers concluded that asparagusic acid and its derivatives are the precursors of urinary odor (compared, in different scientific papers, to the smell of "rotten cabbage," "boiling cabbage" and "vegetable soup"). The various compounds that contribute to the distinct smell—and were sometimes blamed as the sole cause in the past—are metabolized from asparagusic acid.

Exactly how these compounds are produced as we digest asparagus remains unclear, so let's turn to an equally compelling, but more answerable question"¦

Why Doesn't Asparagus Make Your Pee Smell Funny?

Remember when I said that some people don't produce stinky asparagus pee? Several studies have shown that only some of us experience stinky pee (ranging from 20% to 40% of the subjects taking part in the study, depending on which paper you read), while the majority have never had the pleasure.

For a while, the world was divided into those whose pee stank after eating asparagus and those whose didn't. Then in 1980, a study complicated matters. Subjects whose pee stank sniffed the urine of subjects whose pee didn't. Guess what? The pee stank. It turns out we're not only divided by the ability to produce odorous asparagus pee, but the ability to smell it.

An anosmia (an inability to perceive a smell) keeps certain people from smelling the compounds that make up even the most offensive asparagus pee, and like the stinky pee non-producers, they're in the majority.

Producing and perceiving asparagus pee don't go hand in hand, either. The 1980 study found that some people who don't produce stinky pee could detect the rotten cabbage smell in another person's urine. On the flip side, some stink producers aren't able to pick up the scent in their own urine or the urine of others.

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Big Questions
What Are Carbohydrates Used for In Our Bodies?
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What are the carbohydrates used for in our body?

Ray Schilling:

Carbs are varied. There are complex carbohydrates that are absorbed slowly and you hardly get an insulin reaction. On the other end of the spectrum there are refined carbs like sugar, which are rapidly absorbed in the gut and to which the body reacts swiftly with an insulin reaction to lower high blood sugars.

Generally speaking all carbs are broken down into glucose and absorbed in the gut. Glucose is the fuel that is metabolized inside the cells in the mitochondria to give us energy. This is particularly important in the brain, which lives solely by glucose as its energy supply, but our muscles, our heart, our liver, and kidneys are all very rich in mitochondria for the metabolism of glucose.

But there is a dark side to refined carbs that we need to know about: When all our glucose storage spaces in the liver and the muscles are full (glycogen is the storage form of glucose), then the liver starts processing glucose. With our sugar consumption having spiraled upwards in the last 183 years, this surplus sugar metabolism is causing more and more problems.

The liver produces triglycerides from the extra sugar and LDL cholesterol, the bad cholesterol. This causes hardening of the arteries and causes heart attacks, strokes, and high blood pressure.

We need to come to our senses and cut out processed foods (which have extra sugar in them), switch to a Mediterranean diet and only consume complex carbs, contained in legumes, vegetables, and fruit. It is also recommendable to cut out starchy foods with a glycemic index of higher than 55 in order to bring our liver metabolism back to normal (normal triglyceride and LDL cholesterol production). This will mean cutting out pasta, potatoes, rice, bread, and muffins.

If you're wondering what kind of recipes you could follow, I have included one week’s worth of meals in this book: A Survivor's Guide To Successful Aging: With recipes for 1 week provided by Christina Schilling.

This post originally appeared on Quora. Click here to view.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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