The effect of eating asparagus on one's urine has long been known. Marcel Proust claimed that asparagus "...transforms my chamber-pot into a flask of perfume." Certain constituents of asparagus are metabolized giving urine a distinctive smell due to various sulfur-containing degradation products, including various thiols, thioesters, and ammonia. Derivatives of asparagusic acid are also found in urine. The speed of onset of urine smell has been estimated to occur within 15-30 minutes of ingestion. All individuals produce the odorous compounds after eating asparagus, but only about 40% of the population have the autosomal genes required to smell them.