The latest of the food science graphics looks at the chemistry of beetroot. An unusual effect of beetroot is that it can cause ‘beeturia’, or a red colouration to the urine, after ingestion. This is a condition that only affects an estimated 10-14% of the population, so what are the chemical compounds behind it, and why isn’t it a universal effect?
Perhaps unsurprisingly, it’s the compounds that give beetroot its red colour that can also lead to red-coloured urine. Beetroot’s deep red appearance is due to the presence of a class of compounds called betacyanins. This class comprises a number of compounds with similar chemical structures; betanin is a major player as far as colouration goes, and is actually extracted from beetroots and used as a food colouring (named ‘Beetroot Red’ and designated with the E number E162). Another family of compounds present are the betaxanthins. These have a yellow colour independently, and are present in lower concentrations than the betacyanins.
Betacyanins can cause beeturia because they don’t always break down in the digestive system of some people. The reasons for this are still a little uncertain; it has been suggested that, at low stomach acid pH, the compounds are broken down, and that when the stomach acid is not as strong, this does not occur. Therefore, the compounds are able to pass through the remainder of the digestive system, absorbed through the intestinal walls in the colon into the bloodstream, then filtered out by the kidneys and into the urine. Of course, some of the unmetabolised compound may well remain in the colon and wind up giving the delightful effect of purple poo.
It’s possible that the breakdown of these compounds could also be influenced by genetic factors which have yet to be precisely determined. For example, if a person genetically has a stronger acidity in their stomach, they may well break the compound down effectively and never experience beeturia. However, some studies have downplayed genetic factors, and instead suggest that we all excrete betanin in our urine to some extent after eating beetroot, and it is only environmental factors that influence whether or not this concentration is high enough to give a red colouration. In another interesting suggestion, beeturia has been potentially linked to being an early indicator of haemochromatosis (over-accumulation of iron in the body).
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References & Further Reading
- ‘Why isn’t beetroot dye broken down by digestion?’ – The Naked Scientists
- ‘Beetroot Colours’ – Food-Info.net