Asparagus Stench


What’s the deal with the smell in my urine after eating asparagus? Nothing else seems to have this effect. My best friend swears it’s a myth and all in my head. What’s the truth? — D. Ross, Massapequa, NY

It’s very strange, because “Asparagus Piss” is just one of those medical subjects that has no impact on human health whatsoever, but has been controversial since people first started paying attention to stuff like that. The reason for this is that not everyone can smell the urinary byproducts of asparagus; those who can smell them assume everyone else can too, and those who can’t smell them think those who can are crazy.

There’s no question that this is a real phenomenon, appearing in published literature as early as 1731 when John Arbuthnot, a royal physician, wrote that asparagus “affects the urine with a foetid smell.” In 1866 Pierre Larousse wrote in his Universal Dictionary that “the whole world knows the stench (asparagus) produces in the urine.” Always the classy guy, it is said that Babe Ruth claimed asparagus “makes my piss stink” to his hostess at a black tie event. So, ok, it’s real, but what causes it?

When you eat, your body breaks down the food into small packets that it can deal with; proteins are reduced to amino acids, fats are broken down to fatty acids, starches cleaved to produce easily absorbable sugars, and so on. Junk the body can’t use gets expelled as waste products. Waste molecules that are very dissolvable in water will often be excreted in the urine. Despite numerous studies, the actual substance that causes asparagus urine is still a mystery. Researchers have isolated the molecules that you actually smell and they are small, sulfur-containing compounds that are outgassed from urine when it is exposed to air. However, they’re so small that they should have been totally reduced to carbon dioxide and inorganic sulfate by the body, rendering them odorless. This points to a “precursor molecule” . . . something that is dumped into the urine by the kidney and then breaks up when you void your awful bladder to produce the smell. This precursor molecule, after 150 years of off and on (and poorly funded) investigation, has yet to be found.

It’s even controversial whether everyone produces the smell in the first place. It is widely known that up to 67% of the population are “non-smellers,” meaning they can’t detect asparagus in even the most noxious urine (imagine how you would actually do a study like this. It’s fun to think about), but it has never been determined conclusively whether everyone who eats asparagus even produces the stench. Some studies say yes, some are not so sure. A 1987 study showed that only 47% of people were “producers” but other studies have shown this number to be 100%. It may be that different study populations are simply different genetically. A team in Finland may get a very different result than an American team; you’d think this would be an easy thing to figure out, but it tends to be hard to keep your research grant money going when you’re exploring “frivolous” topics like asparagus stink.

All this “only some people produce stench and only some people smell it” malarkey keeps the mystery going. I’m afraid the riddle will endure until someone discovers a link between malodorous asparagus whiz and a serious health condition, or until someone can figure out a way to make a lot of money off of it.

**Remember, don’t do anything you read here without first consulting with your own health care provider.**

Dr. Steve is the resident medical expert for the Opie and Anthony and Ron and Fez shows, and the host of his own Sirius XM Radio program, Weird Medicine.

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