Anecdotal observations scattered throughout the literature have often provided clues to underlying variations in humans' ability to handle dietary chemicals. Beetroot, the red root of the garden beet used extensively as a food source, is known to produce red urine in some people following its ingestion, whereas others appear to be able to eat the vegetable with impunity. Asparagus, a vegetable whose young shoots have been eaten as a delicacy since the times of the Roman Empire, has been associated with the production of a malodorous urine smelling like rotten cabbage. Those who produce this odor assume that everyone does, and those who do not produce it have no idea of its potential olfactory consequences. These two examples, where the population appears divided in its ability to process food products or more precisely the chemicals contained within them, are reviewed in detail in this article.