Why does asparagus make your pee stink?

Originally published on pg. 6 of the Santa Monica Daily Press Newspaper
To smell asparagus pee or not to smell asparagus pee? That is the question.

According to popular asparagus pee research, up to 76 percent of the population make stinky asparagus pee, but some of them are simply not able to smell it while others literally have a nose for that distinct scent. Those of you who are neither smellers or excreters are probably reading this and thinking, “What the heck is she talking about? This chick is crazy!”

A few weekends ago I took a trip with some friends to the middle of California, also known as Paso Robles which, I learned, is known for its wine country. Having lived in northern California, I visited Sonoma and Napa and toured some of the vineyards. As I recall, the vineyards kind of blended together, or perhaps it was the consumption of wine that made it seem that way.

But in Paso Robles, my friends and I visited only four wineries, each with a very distinct and unique nuance; from the former Penn State (my Alma mater) football player owned Eberle Winery with the wild boar statue outside the entrance, to the Eagle Castle Winery which is literally a castle complete with a mote.

My favorite part of the trip though, since I am not a big wine drinker, was our stay at the beautiful La Bellasera hotel, and dining at the on-site Enoteca Restaurant. I even ordered filet mignon for dinner which was wonderful. However, what I enjoyed most about the meal was the roasted asparagus with balsamic reduction and coarse salt. I had a double order and ate every last spear. Ten minutes later, when I had to use the facilities, I laughed at the haste with which the “asparagus pee” presented itself. This reminded me that I have always wanted to investigate and write about the “asparagus pee” phenomenon.

I was telling my running partner that I was writing an article about asparagus pee. I know, dream big, right? I told him that the one thing I learned from my research is that some people have stinky pee immediately after eating asparagus and some do not. And he pointed out something I found very interesting. He said, “What if having the enzyme to break down asparagus to its smelly demise means that you also have some sort of “protection” that non-stinky pee’rs do not have?”

I said, “Wow! You make an interesting point. There is research for everything. Let me see what I can find.” It’s funny what you will talk about while trying not to think about the fact that you are running even when your body says, “You probably should have taken today off.”

After further investigation, I found that I am not the only one wondering what causes “asparagus pee,” and that no one has inconclusively answered the question.

There are several metabolites left in the urine after eating asparagus, many of which contain, as part of their long name, either methane or sulfur, but both translate into “stinky.” Specifically they are: methanethiol, dimethyl sulphide, dimethyl disulphide, bis-(methylthio) methane, dimethyl sulphoxide and dimethyl sulphone. Which one makes such a stink is still unknown.

One study did find that methylmercaptan appeared in the urine of 40 percent of study participants and that its excretion was an expression of an autosomal dominant gene. (Meaning that you only had to get the “stinky asparagus pee” gene from one parent in order to have it passed down to you.) In case you want to know who to blame, you would have to serve asparagus at your next family dinner and then use the bathroom after each parent. Gross, I know.

Sometimes the “smell” emitted from an individual, can be used to diagnose a clinical symptom or life-threatening in-born error of metabolism. For example, I’m sure you’ve seen the warnings on diet soda cans “Phenylketonurics- contains phenylalanine.” This warning is usually found on any product that contains Aspartame because Aspartame is a source of the amino acid phenylalanine which is not harmful to the majority but can be life threatening to the minority of people born with PKU or Phenylketonuria. Apparently, individuals born with PKU, give off an odor like a “sweaty, stale locker room.”

PKU is a genetic metabolic disorder inherited when both parents pass the gene on to the infant. Every baby born in the US has their heel pricked and tested at birth to see if they have PKU. It is quite rare, 1 in 15,000. But if not detected and treated, the result can be irreversible brain damage. PKU sufferers have to follow a very strict low-protein diet and have to drink a special formula to ensure they meet their nutrition needs without the inclusion of the otherwise essential amino acid: phenyalanine.

But to put your mind at rest, PKU is rare and would be detected within the first year of life. Those who have the gene to make stinky asparagus pee, however, may not even know they have it until they eat asparagus, and then pee, of course. I never had asparagus until I was working as food service manager at a college and the chef made asparagus spears tied with an orange peel for a special dinner. I ate asparagus and was completely taken aback by how much I loved it. I was also saddened by the fact that I had missed out on eating it for the first 25 years of my life. I can’t recall if my pee smelled that first time though.

If you too have the gene to make stinky asparagus pee, don’t worry about any long term side effects except for the occasional malodorous urine which arrives quickly after asparagus ingestion and therefore, may temporarily offend the person in the stall next to you even at the finest restaurant in town. Oh, well. C’est la vie. That’s the price we pay for consuming those lovely little green spears. We still don’t know if being an stinky asparagus pee sufferer confers extra protection or not but one can only hope. There should be some health benefit to counter that smell, right?

To make some stinky asparagus pee of your own, try this recipe.

Roasted Asparagus with Balsamic Reduction
1 pound asparagus, thick spears
1 Tablespoon high-heat oil (sunflower, safflower or canola)
2 cloves garlic, minced
Ground black pepper
Coarse kosher salt

Preheat oven to 400 degrees

Snap ends off of asparagus. Place spears on baking sheet. Drizzle with oil, garlic, salt and pepper and roll to coat evenly. Roast for eight to 10 minutes until lightly browned and tender.

Balsamic Reduction
16 ounce bottle of balsamic vinegar
1/2 teaspoon sugar

Pour vinegar in a sauce pot set on high heat. When the vinegar begins to boil, reduce to medium. Add sugar and dissolve. Simmer uncovered until the vinegar has reduced by 75 percent. Dip a spoon in the reduced vinegar. The reduction should stick like syrup. Pour over roasted asparagus, over poached fruit or meat/poultry of your choice.