Why does your pee smell after eating asparagus? Experts explain

Asparagus is the perfect spring vegetable. It’s crisp and tender and can be used in everything from salads to soups to pasta dishes. It is also rich in nutrients, including folic acid, calcium and antioxidants, including vitamins C and E. The only downside: asparagus seems to cause an unpleasant odor in our urine.

What causes the odor? How long does it usually last?
Dr. Christopher Smith, associate professor of urology at Baylor College of Medicine, told Yahoo Life that asparagus contains asparaginic acid, an odorless acid that breaks down into “volatile sulfur-containing byproducts. The rapid evaporation of asparagus metabolites when you urinate can cause your urine to smell like sulfur, like rotten eggs or cooked cabbage.

According to Smith, the odor “can start 15 minutes after ingestion and last up to 14 hours. But the exact compound or how much of it causes it remains unknown.

Why can’t everyone smell it?
So why is it that only some people seem to smell this strong odor after eating asparagus? Two hypotheses exist. One is that some people do not produce the odor at all. A small study in 2010 showed that “about 8% of people have no or only a small amount of enzymes to break down asparagine acid. Therefore, they don’t produce smelly urine,” Smith said.

Another hypothesis is that everyone produces odor, but they may not actually smell anything. A 2016 study found that whether someone can smell asparagus urine was linked to genetic variants near multiple olfactory receptor genes. The study looked at nearly 7,000 European and American participants and found that about 62 percent of women and 58 percent of men had asparagus olfactory deficiency, a genetic modification that means “they can’t perceive or smell toxic urine,” Smith noted.

Because women are usually better able to detect odors, some women may be too polite to mention the smell, or may not notice it because of their position when they urinate. More research on metabolism and genetics is still needed to determine the exact cause of these differences.

Are there any other vegetables that can change the odor of urine?
Asparaginic acid is only found in asparagus, though Smith says there are many other foods that can change the odor of urine. For example, garlic, onions and Brussels sprouts all break down into sulfur compounds when they are digested. These foods also produce methyl mercaptan, a gas with the smell of rotting cabbage, which is released when urinating and breathing.

Is there anything I can do to prevent the odor before eating asparagus?
According to Smith, unfortunately not. He says, “If they have enzymes in their bodies, they can’t stop the breakdown of asparagus acid.”

If you really can’t stand the smell, Smith recommends either eating less asparagus or drinking more water to try to dilute your urine and the smell. Despite the unpleasant odor, it is still recommended that you continue to enjoy asparagus so that you can reap all of its health benefits.