2,728 People Took An Online Survey About Asparagus Pee
Here’s what they said.
At the start of the northern hemisphere asparagus season, we posted a video about The Mystery of Asparagus Pee on MinuteEarth, our YouTube channel. We also wanted to help solve the mystery, so we asked our viewers to take a survey (thanks!). We got a self-selected, non-random sample of 2,728 people. Now, as asparagus season is winding down, so too is our peesearch. Our results below have not been pee-reviewed, but we hope that you appreciate them for what they are. Moreover, we hope that they inspire you to learn more — about asparagus pee, about other topics, and about the scientific pursuit of knowledge!
Urine for a treat!
The MinuteEarth Team
How often do you eat asparagus?
Most participants eat asparagus occasionally. Seventy people said, “I’ve never eaten it! Why am I taking this survey?” We appreciate that they took the survey anyway, but we had to remove their results for obvious reasons.
Does your pee smell different to you?
Seventy-two percent of participants reported that their pee smells different after consuming asparagus. That’s a much higher percentage than the 40–43% of people who reported being able to smell asparagus pee in early studies (see Mitchell et al. 1987). And it’s closer to but still higher than the 63% of participants who reported the ability to smell asparagus pee in a recent self-selected survey (Ericksson et al. 2010; see a related summary). However, Ericksson et al. 2010 surveyed a number of human traits, while we focused on asparagus pee; MinuteEarth viewers who had noticed asparagus pee in their own life may have been especially likely to respond to our survey.
Perhaps unsurprisingly, people who reported eating asparagus “very rarely” were the least certain about the vegetable’s aromatic influence on their urine, while people with a more frequent asparagus habit were more likely to have noticed an odor.
What part of the asparagus stalk do you normally eat?
Nearly all participants eat the entire stalk.
Asparagusic acid, a sulphur-containing molecule unique to asparagus, is the likely precursor to the odorous molecules that emanate from urine following asparagus ingestion (Mitchell and Waring 2014). Our findings seem to support its role, as asparagusic acid is found in higher concentrations in the top of the stalk than the bottom (Mitchell and Waring 2014), and we found that 66% of participants who eat only the top have noticed a different odor in their pee, compared to 47% among those who eat only the bottom.
However, 73% of people who eat the entire stalk have noticed a different odor in their pee, a greater percentage than among people who eat either the top or the bottom. We didn’t ask about the quantities of asparagus people typically eat (oops), but if people who eat the entire stalk eat more asparagus per sitting than people who eat only part of the stalk, they may also consume more asparagusic acid, and therefore have smellier and more noticeable pee.
How long after the meal does the smell first show up?
For nearly half of participants, the odor appears within 2 hours; some participants noted that it appears remarkably fast, in 10–15 minutes, and wondered how that was possible. We wonder too! Water can enter the bloodstream within that time (Péronnet et al. 2012), so the odorous compounds in asparagus might be able to make it to the bladder that quickly as well.
For how many hours does your pee smell?
The odor duration was centered around 6 hours, with roughly half of participants reporting odor in their pee for 2–12 hours.
Among participants who knew both how long it takes their pee to start smelling and how long the smell lasts, 93% said it starts smelling within 6 hours. Nearly three-quarters of people said it starts within 6 hours and lasts for 2–12 hours.
Age, Sex, and Asparagus Pee
Younger participants have less knowledge about the occurrence, onset, and duration of asparagus pee, perhaps because they have had fewer opportunities to smell it. There also seems to be some self-selection happening, as a remarkable 100% of the oldest participants have noticed asparagus odor in their pee. They may have been encouraged to participate in part based on their personal experience noticing the odor, and in part based on their reported tendency to experience the odor rapidly and for a long duration, compared to the younger groups. Alternatively, these results may indicate changes in how the body processes asparagusic acid or other odor-producing molecules as it ages (however, Mitchell et al. 1987 note that production of asparagus pee can last throughout an individual’s life).
The biological (assigned) sex of participants does not significantly influence whether they have smelled, haven’t smelled, or don’t know if they have smelled asparagus odor in their pee. The onset and duration of asparagus pee are also similar across males and females. This all fits with our not having seen any published reference to asparagus pee differences by sex.
Asparagus Pee and Other People
More than half of participants have never noticed anyone else’s asparagus pee, and a majority have never had anyone notice their asparagus pee, which may tell us more about social norms for toilet privacy than than anything else.
Perhaps more interesting were the 34 people who reported having been told that they had stinky asparagus pee, but who haven’t noticed the smell in their own urine. The fact that these people exist, even if they make up less than 2% of our sample, suggests that some people may produce stinky asparagus but are incapable of smelling it. There were also 50 respondents with a functioning sense of smell and a familiarity with asparagus pee odor (having noticed it in others’ pee) but who have never noticed a funk in their own pee or had anyone else detect one; some people may be able to eat asparagus without producing an odor.
Among participants who have both noticed others’ asparagus pee and had their own pee noticed by others, if participants notice family, family notices them; if participants notice non-family, non-family notices them; and if participants notice both family and non-family, both family and non-family notice them. This may have more to do with whether participants share bathrooms, and therefore asparagus pee odors, with family, non-family, or both, than with an underlying genetically-determined ability to produce or smell asparagus pee, although Ericksson et al. 2010 found that the detection of asparagus pee (as opposed to its production) does associate with a particular set of genes.
Are there any other foods that make your pee smell different?
Almost 10% of you said that coffee makes their pee stink! And 2% or fewer of you listed a number of other foods or ingestible items, including: tuna and chicken, beer and other alcohols, onion and garlic, Brassica oleracea (broccoli, brussels sprouts, cabbage, etc.), breakfast cereals such as Honey Smacks, beetroots, pineapples and other fruit, antibiotics and other medications, vitamins and supplements, and Parkia speciosa (Southeast Asian “stink bean”). That’s a lot of different items, but asparagus is still the stinkiest, with 72% of participants noticing its effects!
Here are some other things you wanted to tell us
Note: We edited some responses for clarity
Anecdotal Insights
- I am 29 years old and was not able to smell asparagus pee until about 3 years ago. It was like a light switched — one day I couldn’t smell it, next time I ate asparagus the strong smell was there.
- As for hours my pee smells… more like days. Sometimes 2 days.
- Even a small amount (such as asparagus as a topping on pizza) will make my pee smelly.
- I think, that even my sweat smells a bit like asparagus pee, after eating asparagus.… If the smell is also noticeable in sweat, maybe it doesn’t have anything to do with the pee itself, but with digestion or the absorption of specific nutrients. Or bacteria in the intestinal tract, not in the pee.
- I have 4 kids, my wife and I smell/produce, and my 4 kids do too.
- Sister and mother have the strong urine smell after eating asparagus, but father and I do not.
The Appeal of the Odor
Some people spoke out strongly against the smell of asparagus pee…
- I avoid eating asparagus, even though I enjoy its taste, because I hate the asparagus pee smell.
- I no longer consume asparagus as the smell of my urine afterwards makes me feel very ill indeed.
While others, Proust-like, came to its defense…
- It doesn’t really “stink” — it just smells different.
- It’s not a disgusting smell. In discussions with with friends and family there are some that really hate the smell and some don’t.
Geographic Notes
- In India we eat asparagus quite frequently, the concept of pee smelling different is completely new to me. I heard about this on this video for the first time. I have never heard anyone out of the the billion people talking about this phenomenon.
- I think the first question needs the option “Regularly during asparagus season”. Then again, I’m from Germany, where asparagus season has some kind of cult status.
Fun
- Asparagus is not good with eggs as your video suggested. Try it with chicken breast.
- By some miracle, my three-year-old loves asparagus.
- My dog loves asparagus!
- Science is now hilarious to my 5 year old, thanks to this video.
- What do you call it when asparagus feels glum? Despairagus!
The Process
- Thanks for the research, this topic has interested me for years!
- Doing a survey is a really cool idea. Keep up the awesome work and lots of love!
- I like being engaged! More surveys!
- You guys deserve an Ig Nobel Prize for this.
- Keep peeing the best!
We appeeciate that so many peeple peeticipated in the survey, and that you read to the end of our peesults! We needn’t remind you, but Don’t Forget to Pee Awesome #DFTPA
Alex Reich, Rachel Becker, and Emily Elert designed the survey. Alex Reich and Emily Elert organized data. Alex Reich analyzed data and wrote the results. Rachel Becker, Ever Salazar, Henry Reich, David Goldenberg, Kate Yoshida, and Peter Reich provided input on the survey, analysis, and write-up.
