Why Does Asparagus Make Your Pee Smell?
There's a lot to love about asparagus: It's crispy, earthy, and downright delicious. The veggie can also be enjoyed in a myriad of recipes, such as chilled soups, salads, frittatas, and more. The only catch? Eating asparagus can make your urine smell very stinky, to the point where you might want to skip the veg. In fact, the smell of "asparagus pee" is so distinct that people — including Benjamin Franklin — have been writing about it in literature for hundreds of years, research shows.
So, why does asparagus make your pee smell? As it turns out, there's a scientific reason why you might produce — and be able to smell — asparagus pee. Here, dietitians break down exactly why asparagus makes your pee stink and what you can do about it. (Related: 5 Reasons Why Your Poop Smells So Bad)
What Is Asparagus Pee?
Before diving into why asparagus makes your pee smell, you first need a bit of background on what asparagus is, exactly. A relative of onions, leeks, and garlic, asparagus is a spring vegetable that hails from the Mediterranean, according to information published by the University of Illinois. There are about 300 varieties of asparagus, including green, purple, white, and pink cultivars, according to a 2020 scientific review published in the journal Metabolites. However, green asparagus is most commonly found in the U.S., and you'll likely pick up stems (aka spears, the edible part of the plant) of the green "Martha Washington" variety in most grocery stores.
After eating asparagus of any kind, though, you might develop "asparagus pee" — aka smelly, odorous urine. It's certainly not a medical term, but the phenomenon is so widespread — and, uh, stinky — that it's become commonly used. Of course, urine doesn't normally smell like roses, to begin with, but what makes asparagus pee so noteworthy is its pungent, unpleasant odor that can be compared to rotten eggs and garlic, says Annamaria Louloudis, M.S., R.D., a registered dietitian at Culina Health. It might also smell sour, acidic, and/or tart, depending on your sense of smell. In other words, the scent is foul AF.
Why Does Asparagus Make Your Pee Stink?
Although the scent of asparagus pee might make you do a double take, know that it's a result of normal digestion, so there's no need to freak out. Basically, "asparagus contains a chemical compound called asparagusic acid," explains Louloudis. "When you eat asparagus, your body breaks down this chemical into sulfur-containing compounds." (BTW, sulfur is a chemical element that smells like — surprise — rotten eggs.) These compounds, along with other waste products, are then excreted via the urine, resulting in odorous pee. Furthermore, "sulfur-containing molecules [readily] vaporize at room temperature, allowing them to easily travel from urine into the air," says Louloudis. That's why you might find yourself wrinkling your nose before you even flush the toilet.
Asparagus pee can also develop surprisingly quickly. You might be able to detect the odor in your urine approximately 15 to 30 minutes after eating the veggie, and the foul smell might stick around for up to 14 hours, says Louloudis. Exactly how long you experience asparagus pee depends on several factors, however, such as how much asparagus you ate and how often you're peeing, adds Ehsani. For example, if you're well-hydrated and drinking lots of fluids, you might urinate more frequently, ultimately flushing out the smelly compounds more quickly and reducing how long you have to deal with stinky asparagus pee, says Ehsani. That said, it's different for each person, as how your body processes asparagus also matters, she adds. (More on that last bit in a sec.)
Does Everyone Have Smelly Asparagus Pee?
Now, here's where things get interesting. Although asparagus pee is common, "not everyone develops smelly pee after eating asparagus," says Roxana Ehsani, M.S., R.D., C.S.S.D., L.D.N., a registered dietitian. That's because some people might be able to break down the sulfur-containing compounds (which, again, is a byproduct of asparagusic acid in asparagus) more efficiently than others, she notes, though there isn't currently research explaining exactly why some folks have this ability. Consequently, these individuals' post-asparagus urine may contain fewer sulfur-containing compounds, resulting in not-so-smelly pee.
In other cases, it's less about digestion and more about your own ability to smell. Even if you do produce sulfuric byproducts after eating asparagus, you may be unable to smell them in your urine — a condition called asparagus anosmia, says Ehsani. (ICYDK, anosmia, as a general condition, is the inability to detect odor, according to the National Library of Medicine.) Asparagus anosmia specifically is caused by a genetic variation that alters olfactory (re: smell) receptors so you're unable to perceive the sulfuric odor, explains Ehsani. If you have this condition, your urine might just smell like regular ol' pee (to you, at least) even if your urine contains post-asparagus sulfuric compounds.
Other factors can also affect your experience with asparagus pee. For example, folks who sit down to pee may be less likely to detect the smell, as this urination position potentially reduces their exposure to stinky compounds, according to a 2016 study in the journal BMJ. It may also be as simple as having a very low concentration of sulfur-containing compounds in your urine, says Ehsani. This can happen if you consumed large quantities of other foods and drinks with a small serving of asparagus, she says. For example, "if you eat a small amount of asparagus — just a spear or two [in] a large veggie medley — it would result in a very low concentration of sulfur compounds in the urine and the smell may be undetected," she explains. Similarly, if you're drinking plenty of fluids, the smell may be less noticeable because you're producing more pee and excreting the compounds more quickly.
Can You Prevent Asparagus Pee?
Sorry, folks: If you develop stinky pee after munching on asparagus, there's nothing you can do to prevent it, says Louloudis. For starters, you can't change the way your body digests food, so it's impossible to stave off the production of sulfuric compounds. Similarly, since you can't control your genes, you can't change your olfactory receptors' ability to detect those smelly molecules. However, you can make your urinating experience a bit more pleasant by drinking more fluids — and, in turn, peeing more often — to flush the stinky compounds out more quickly. You can also try reducing your exposure to the foul compounds by sitting down while urinating or, at the very least, turning your head the other way as you flush.
But remember, asparagus pee is completely normal and shouldn't be a cause for concern. It also doesn't mean the vegetable is "unhealthy" or should be avoided altogether, says Ehsani. "You can — and should — still eat asparagus, even if you have smelly pee after," she adds. Asparagus, after all, is chock-full of essential nutrients, including gut-friendly fiber, bone-supporting vitamin K, and folate, which helps support healthy pregnancies. Translation: The health benefits of asparagus make the stinky pee worth it — even if you do have to pinch your nose after taking a leak.