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Have you eaten asparagus and noticed that it can alter how your urine smells? Perhaps you’ve heard about the phenomenon but wondered why it doesn’t seem to affect you. Or maybe you’ve eaten beetroot and then been worried there appeared to be blood in your water. Why do certain foods change our urine and does it make a difference to our health?
Observations of how what we eat can affect our pee can be traced back through history, from the ancient Greeks including Antiphon and Theophrastes to an early edition of the medical journal The Lancet in 1836. But asparagus’s potential to affect urine was not formally described until 1735.
This happened to coincide with the British agrarian revolution when fertilisers containing sulphur were first used on crops, although there is no real evidence to say if this effect is causal.
There have been different theories put forward over the years explaining why only some people notice a smell in their urine after eating asparagus. It was first thought that some people broke down the vegetable in a way that released a smelly chemical in the urine.
In the UK, data suggested about half of the population were so-called “excretors” in this way. This led to a theory that the characteristic was carried by a dominant gene that only needed to be inherited from one parent.