After eating beets. The colour of beetroot is due to a family of compounds known collectively as betacyanins. Ingestion of beets can result in a bright red discolouration of the urine, and quite a scare for the urinator who may confuse it with blood! Blood in the urine is a frightening prospect and a possible sign of serious disease while the presence of betacyanins is benign and possibly even healthy.
Not everyone produces red urine after eating beets which has led many researchers to believe that production is genetically determined. Experiments have, however, cast doubt on this explanation. When subjects are given a fixed amount of beetroot to eat, and their urine is chemically analyzed, they all show the presence of betacyanins, but in some cases in amounts too small to impart a visual effect. When the dose is increased, subjects who were visually “nonexcretors” begin to produce red urine. Furthermore, when subjects ingest the same amount of beetroot on separate occasions, they produce urine of varying shades of red. Factors other than genetics are obviously involved. Times of planting and harvesting greatly influence betacyanin content so that beets purchased at different times may have different effects.
Betacyanin colour also is dependent on acidity, being more stable under reduced acid conditions. At the normal pH of the stomach, about 2, rapid decomposition of beet pigment occurs. If the acidity is reduced, such as by taking drugs for excess stomach acid, the chance of excreting red urine is increased. In one reported case, a gentleman who had never previously experienced the red urine phenomenon, suddenly displayed red urine after a course of ranitidine, a drug used to reduce stomach acidity. The presence of iron in the form of ferric ions in the stomach and intestines can also prevent the beetroot colurants from being absorbed into the bloodstream. Since iron can be complexed by oxalic acid or by ascorbic acid (vitamin C), these compounds which are widely distributed in foods can also determine whether beet ingestion will produce red urine.
There seems to be enough evidence here to suggest that the production of red urine after eating beets is not under genetic control, but rather is a function of stomach acidity and the presence or absence of other dietary components. Researchers at the University of Wisconsin have discovered that not only is beet induced red urine not a matter of concern, it may be healthy. Beet extracts have been found to stimulate the liver’s production of phase II enzymes which are know to have cancer protective properties. This has been shown in mouse liver cell assays, but such experiments are known to be good models for what happens in the human liver. Since beet pigment shows up in urine, it must be absorbed from the digestive tract into the bloodstream, and therefore can increase phase II enzyme levels.
Eating beets may therefore provide some protection against cancer. Incidentally, turning beet red in the face is solely a matter of embarrassment and has nothing to do with eating beets.