Q: Why does urine have a bad odor after a person eats asparagus?
A: Researchers have actually studied this question extensively, but are not in complete agreement on the answer. The chemicals in asparagus that probably cause the odors are S-methylmethionine and asparagusic acid, which are converted in the body into a number of compounds that contain sulfur, including methanethiol, dimethyl sulfide, dimethyl disulfide, dimethyl sulfoxide and dimethyl sulfone. It is probably a combination of these chemicals that produces the distinct odor.
The ability to convert S-methylmethionine and asparagusic acid into these odoriferous chemicals is genetically determined, and only about 40% of the population is capable of doing so. The ability to perceive the unique smell is also genetically determined, and is found in only about 10% of the population.