Asparagus is the perfect springtime vegetable. It’s crunchy yet tender and can be used in everything from salads and soups to pasta dishes. It’s also packed with nutrients, including folic acid, calcium and antioxidants, including vitamins C and E. The only downside: Asparagus seems to cause an unpleasant smell in our urine.
What causes the smell? And how long does it typically last?
Asparagus contains asparagusic acid, an odorless acid that breaks down into “volatile sulfurous byproducts,” Dr. Christopher Smith, associate professor of urology at Baylor College of Medicine, tells Yahoo Life. The quick evaporation of those asparagus metabolites when peeing causes your urine to have a sulfurous odor, like rotten eggs or cooked cabbage.
According to Smith, the odor can “begin as early as 15 minutes after ingestion and last up to 14 hours.” But the exact compound or how many are causing it is still unknown.
Why doesn’t everyone experience the smell?
So why do only some people seem to experience this strong odor after eating asparagus? Two hypotheses exist. One is that some people simply don’t produce the smell. A small 2010 study showed that “about 8% of people have none or only small amounts of enzyme to break down asparagusic acid. Thus, they don’t produce smelly urine,” says Smith.
The other hypothesis is that everyone produces the odor, but they may not actually smell anything. A 2016 study found that whether or not someone could smell asparagus pee is associated with a genetic variation near multiple olfactory receptor genes. The study looked at nearly 7,000 European American participants and found that about 62% of women and 58% of men had asparagus anosmia, a genetic modification that means “they could not perceive or smell the noxious urine,” notes Smith.
Since women are generally better able to detect smells, it’s possible some women were either too polite to mention the smell or didn’t pick up on it due to their position while peeing. More research still needs to be done on metabolism and genetics to determine exact causes of these differences.
Are there any other vegetables that change the odor of your urine?
Asparagusic acid is only found in asparagus, though Smith says there are plenty of other foods that can change the smell of your urine. Garlic, onions and brussels sprouts, for example, all break down into sulfur compounds when digested. These foods also produce methyl mercaptan, a gas that has a rotten cabbage odor and is released when peeing and breathing.
Is there anything you can do before eating asparagus to prevent the smell?
Unfortunately no, according to Smith. He says that one “cannot prevent the breakdown of asparagusic acid if they have the enzymes present in their body.”
If you really can’t take the smell, then Smith recommends either eating less asparagus or drinking plenty of water to try to dilute your urine and therefore the smell. Despite its unfavorable odor after you eat it, it’s still recommended to keep enjoying asparagus so you can reap all of its health benefits.
Maxine Yeung is a registered dietitian and personal trainer.
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