The reason why some people can smell asparagus in their urine after they've eaten it and others can't has been discovered.
When the digestive system breaks the vegetable down into smaller compounds, a distinct smell is produced.
One such compound - mercaptan - is also found in rotten eggs, onions and garlic and has a potent sulphur-like odour.
But whether or not an adult can recognise this smell in their urine is all down to their genes, scientists claim.
However, women are less likely because they sit down to go to the toilet, a study found.
US scientists conducted research on 6,909 men and women of European-American descent.
Findings published in the British Medical Journal show that two fifths of participants agreed they could smell a distinct odour in their urine after eating asparagus.
But three fifths could not - known as 'asparagus anosmia'. And men were more likely than women to be able to smell it.
Lead researcher Professor Lorelei Mucci, from Harvard University, said the findings could be due to 'modest women'.
He said they may be loathed to admit they can smell the distinctive odour in their urine.
While he also suggested that their position during urination might reduce their chances of smelling the odour.
The researchers analysed the genome - the complete genetic map of a person - to find genes that were associated with asparagus anosmia.
They found several genes that are likely to play a role in smelling asparagus in urine.
But they are still unsure as to why people would have developed the ability to smell asparagus in urine.
One theory is it may have helped our ancestors sniff out a healthy source of food.
Professor Mucci said: 'Asparagus is rich in iron, fibre, zinc, folate, and vitamins A, E and C.
'Consumption of asparagus, as part of a diet high in vegetables, has been hypothesised to reduce the risk of cancer, cognitive impairment, and cardiovascular related diseases.
'Asparagus is not all contentious: make sure to serve the leaves as well to protect the liver against toxic insults so that you can enjoy your holiday nights and potentially alleviate that hangover the next day.'
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