Though we ate asparagus fairly often in my house while I was growing up, and though I noticed that occasionally my urine would smell funny, it wasn’t until I was 20 years old and on Semester At Sea that I finally put the pieces together. I remember the circumstances well: the lunch buffet featured cream of asparagus soup and the bathrooms stank to high heaven. I finally realized that asparagus makes your pee smell funny.
Today, several hours after I had tuna for lunch, I noticed that my urine had a definite tuna aroma. Which led me to wonder two things: how many other foods have an impact on urine odor, and by what means do these foods have this effect?
As I mused on the first question to Aurora, we realized that we couldn’t come up with any other culprits off-hand, though, as the first 20 years of my life go to show, is far from iron clad evidence that others don’t exist. The one observation Aurora did make is that “beets make your poop turn red.”
“Maybe,” I countered, “but they’re a solid food and exert an effect on your solid waste,” which is much less of a stretch of the imagination to figure out than how solid foods impact your urinary composition (though, upon closer reflection, one does realize that every food contains some water, and all foods are broken down into their component molecules via the digestive process), but still, I alleged, “beets don’t turn your pee red.”
Turns out I was wrong. Consulting Harold McGee’s comprehensive guide On Food and Cooking: The Science and Lore of the Kitchen, I came to discover that beets do impact the color of your urine, though usually so minutely as not to be discernible to the naked eye. However, “because the body has a limited ability to metabolize” the betain molecules that give beets their crimson appearance, “a large dose of red beets or prickly pears can give a startling but harmless tinge to the urine.”
Mr. McGee’s only other explanation about food’s impact on the urine comes in relation to our good friend asparagus. Its effect on urine has been noted for centuries; On Food and Cooking quotes Louis Lemery’s Treatise of All Sorts of Foods, which dates to 1702, “‘[Asparagus] cause a filthy and disagreeable smell in urine, as everybody knows.” Except it turns out that not everybody does know it: there is a small portion of the population in whom asparagus doesn’t have this effect, and a somewhat larger number of persons who are unable to smell the asparagus pee stench.
Those of us who do both experience the effect and are able to smell it shouldn’t be surprised that it is caused by “a chemical relative of the essence of skunk smell called methanethiol,” which results when “apparently the body metabolizes a sulfur-containing substance, asparagusic acid.” Fascinating! An acid apparently limited or closely enough related to asparagus that its name is derived from the vegetable. I wanted to know more, but Mr. McGee wasn’t revealing anything further.
Fortunately, there’s some chap out there who writes under the name of Bandolier who wonders about these issues, too, and has examined asaparagus and beets and their effect on urine. It turns out that, though asparagus is the main source of asparagusic acid, it is also “found in a few other food plants, though some non-food plants like tropical mangrove also contain it.” Evolutionarily, it “kills parasitic nematodes, and protects the asparagus plant against them.” Perhaps Bandolier’s most noteworthy observation, though, is “that despite appearing in historical works for about 2,500 years, it was only in the 1700s that it was associated with malodorous urine. This coincided with the use of sulphur-rich fertilizers to improve the flavour of asparagus and onions and garlic.” I can’t recall a urine odor that corresponds to the other two vegetables, but that may be because I haven’t paid attention.
Then again, a quick internet search for information about foods that cause smelly urine turned up a lot of discussion about asparagus and not much else, though I did find a reference that provides more evidence for my ongoing disapproval of low-carb diets: “I noticed recently that I developed an ammonia smell in my urine after going on a low carb diet, the kind of diets which are known for putting bodies in a state of acidosis. The ammonia smell went away when I went off the diet and started eating more carbs, and presumably increased the alkalinity of my body in the process.” Our bodies need complex carbohydrates as its main source of energy; a smart nutritional plan will put emphasis on these foods whilst de-emphasizing heavily processed foods including sugars and simple carbs. But that’s another post altogether.
There was no mention anywhere of tuna causing a distinctive odor in urine. So, now I’m wondering, what other food-related urine odors are going underreported? Please, try to keep one nostril open as you tinkle and let me know what you find out.