How Does Asparagus Make Urine Smell?

If you've ever eaten asparagus, something strange may have happened about 20 minutes after eating it. Perhaps you noticed, perhaps you didn't, but chances are that tasty asparagus side dish left something behind for you. Sure, it's a rather odd token of appreciation, but that popular green veggie called asparagus is known to cause a rather strange smell in the urine of those who consume it.

Asparagus contains a sulfur-containing compound identified by scientists as methyl mercaptan. A colorless gas, this compound is also found in blood, feces, garlic, eggs, cheese and even skunk secretions. In fact, methyl mercaptan is one of the major contributors to bad breath and flatulence odors. In addition, another ingredient found in asparagus is asparagine. Present in foods like dairy products, seafood, poultry, fish and nuts, this amino acid is known to have a distinctive smell when heated. To metabolize both methyl mercaptan and asparagine, the digestive track must break these compounds down and it is this breakdown that's responsible for your urine's strange smell.

Since both methyl mercaptan and asparagine are associated with the sense of smell, there is debate over which ingredient is actually responsible for the asparagus-urine phenomenon. Depending upon whom you ask, some scientists may blame it on the methyl mercaptan while others argue that asparagine is the cause for the odor. Some even think that it's the combination of both compounds. Regardless of the exact culprit, the reason why your urine smells after eating asparagus is simple: because of the way your body breaks it down.

Asparagus is no stranger to debate, and the disagreement over which specific ingredient causes urine to smell is not the only example. Because many people claim that, regardless of asparagus consumption, their urine does not smell, there are multiple theories regarding that as well. The first claims that everyone's urine is in fact affected by asparagus, but only about half of the population have the specific gene that is required to smell the change. On the other hand, the second theory states that only half of the world's population has the gene that's required to break down the compounds found in asparagus and, if the body doesn't break them down, no smell is emitted. Whichever reason is correct, for many people, asparagus will forever be known as the vegetable that makes your urine smell strange.