Submitted by nateblackmt t3_11a9tvk in askscience
Edd1148 t1_j9tbwci wrote
Reply to comment by berliniam in Why is urine yellow? by nateblackmt
Offshoot question: why does asparagus make urine so distinctly pungent?
Dubanx t1_j9th5x6 wrote
Funnily enough, both the ability to smell asparagus pee AND whether or not your pee smells from asparagus is genetic.
Many people can't smell it, and many others don't have pee that smells. A lot of people don't produce a detectable smell after eating it, but the people who claim to smell it have been scientifically shown to agree on which samples smell and which do not. So it's not psychosomatic either.
Zchwns t1_j9tou8g wrote
Do we know whether these genetic traits are dominant or recessive? I’m curious if it’s rarer to have both genetic traits expressed vs no expression of either.
Dubanx t1_j9tqj7x wrote
People's sense of smell & taste tend are known to be heavily dependent on genetic factors, but are super complicated. It's my understanding that these aren't determined by a single gene but the interactions between multiple genes. So they're poorly understood as a result. In general, smell and taste aren't something that gets determined by a single recessive or dominant gene.
For what determines excretion, I just don't know.
Zchwns t1_j9tr1a1 wrote
Interesting! Thank you!
Dubanx t1_j9tst9o wrote
No problem. It's not just limited to asparagus pee too. Taste & Smell are exceptional in how much they vary from one person to another. A famous example is "phenylthiocarbamide". One person spilt some in a lab setting and was confused as to why everyone around him was talking about the smell.
Another example is how certain vegetables, such as spinach, taste terribly bitter to some people and perfectly fine to others. A common trope is a mother screaming at her son/daughter to eat their veggies while the dad sits quietly because he also hates spinach.
Mom lacks the genes which make them taste bad while the children and dad do. The kids aren't just being picky, they literally taste significantly differently between mother and child.
BizzarduousTask t1_j9tuhf1 wrote
And cilantro! For a not-insignificant number of people it tastes like soap!
Elegyjay t1_j9ublnv wrote
And broccoli, cauliflower and Brussels sprouts... the very smell of them cooking makes me gag and I have tried to eat them but can't keep them down.
[deleted] t1_j9tua2m wrote
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GypsyV3nom t1_j9tsldx wrote
Taste and smell have some pretty insane under-the-hood processing that occurs in the brain. There are only about 400 different receptors in the human nose, but the different responses of those 400 receptors to odorants allows humans to detect over one trillion distinct scents. And that's just for humans, who have a relatively poor sense of smell compared to other mammals
adhocflamingo t1_j9u3f3q wrote
Do I understand correctly that there are people who can smell asparagus pee but don’t produce it themselves?
CharlesDuck t1_j9uvse7 wrote
There are two separate superpowers. The ability to smell asparagus pee, and the ability to produce asparagus smelling pee. You can have both, one, or neither power.
Dubanx t1_j9u8xsk wrote
And vice versa, yes. It's hard to distinguish these people, though, since they often don't know what asparagus pee smells like and have nothing to compare it to if they did smell it.
[deleted] t1_j9uh1gs wrote
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oneAUaway t1_j9tlti0 wrote
Asparagus contains a disulfide compound called asparagusic acid, whose metabolites produce the strong odor. Other foods with sulfur-containing compounds (such as cruciferous vegetables like cabbage and broccoli) can produce foul-smelling urine as well, though as u/Dubanx notes, there is a lot of variability in the production and experience of those odors.
lubacrisp t1_j9tmhnr wrote
The breakdown of aspargusic acid into sulphur products that readily evaporate. Sone people can't smell the smell and some people can't make the smell. Both genetic markers
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