Scientists remain divided on why people have different urinary responses to eating asparagus. One camp thinks only about half of the population have a gene enabling us to break down the sulfurous amino acids in asparagus into their smellier components. Others think that everyone digests asparagus the same way, but only about half of us have a gene that enables us to smell the specific compounds formed in the digestion of asparagus.
A recent study found that all asparagus eaters excrete the odorous methyl mercaptan; it is the ability to detect its odor that varies from person to person. The sulfur-containing amino acid methionine is suspected as the precursor in asparagus
can you imagine what people had to do for that study?