When asparagus is digested, it produces a specific metabolite, a volatile compound that is released as a gas-like aroma when you pee. However, some individuals are completely unable to perceive this smell!
As a child, you probably didn’t enjoy eating asparagus, but as an adult, hopefully, you’ve come to appreciate what a delicious and versatile vegetable it can be. If you regularly consume asparagus, you’ve probably also noticed its impact on the smell of your bathroom. This phenomenon, which has puzzled people since asparagus became a part of our diet, consistently makes our urine smell… peculiar! Some people describe it as a stench of rotten eggs, while others find it earthy and fragrant. However, there are individuals who cannot detect this strong scent at all!
Fresh asparagus (Photo Credit: DUSAN ZIDAR/Shutterstock)
If you’ve ever been perplexed by this aromatic assault on your nostrils in the past, by the end of this article, we will unravel the mystery behind this foul-smelling occurrence.
What Causes the Unusual Odor?
If you’ve ever experienced this strange smell after consuming asparagus, don’t worry (or get too excited)… this phenomenon affects everyone who eats it! When we consume food, it enters our body as complex large molecules, which need to be broken down through digestion to become more usable and manageable by the body.
The process of digestion begins as soon as food enters our mouth and continues until we urinate or excrete waste. In between these points, a series of metabolic processes takes place.
During the process of breaking down food, complex molecules are broken down into simpler ones, and byproducts are produced. In the case of asparagus, this vegetable contains a unique compound called asparagusic acid, which is exclusively found in asparagus. When our bodies break down this compound, it produces various volatile sulfur-containing compounds. For a compound to be considered “volatile,” it must have a low boiling point, allowing it to exist as a gas at room temperature.
Asparagusic acid is broken down into dimethyl disulfide, dimethyl sulfide, dimethyl sulfoxide, and dimethyl sulfone. Although these compounds may be difficult to pronounce, they are all volatile and potent, similar to other aromatic compounds that contain sulfur (e.g., rotten eggs!). Within 15-20 minutes of consuming asparagus, these metabolites (substances produced as a result of metabolic processes) are generated. When you urinate, these volatile compounds are released, and the pungent aroma rises to your nose!
Why Can’t Everyone Smell It?
This phenomenon might surprise you, especially the first time you eat asparagus, but if you drag your friends into the room to witness the olfactory experience, some may think you’re crazy. In fact, researchers believe that up to 75% of people are unable to detect the distinct fragrance of these compounds once they are released by the body.
It may be difficult to believe, but it’s important to remember that our senses often work on a range, and each person observes the world in their own unique way. Our perception of color, sensitivity to touch, and strength of hearing can vary. It should come as no surprise, then, that our sense of smell also has some variability.
There are over 400 genes linked to our sense of smell, and with the endless variety of genes, it’s easier to understand why each person has their own distinct olfactory perception. A large-scale study found that variations in a specific gene on Chromosome 1 are likely responsible for the inability to smell asparagus metabolites. This dysfunction, known as specific anosmia, affects about half of the population.
It is believed that specific anosmia has developed because humans primarily rely on their visual sense for survival. Unlike other animals with much more sensitive olfactory senses, our vision is comparatively stronger. Over many generations, genetic variation related to our sense of smell entered the gene pool but had little impact on survival, making it a common trait. Considering the unpleasant odor of asparagus urine, most people should be grateful for their specific anosmia to this scent.
In addition to asparagus, there are other common foods that can cause unusual urine smells. When the body is dehydrated, urine may have a higher concentration of waste products and aromatic compounds, resulting in a potent smell after consuming excessive amounts of alcohol or coffee. Foods high in vitamin B-6, like bananas, chicken, or salmon, can also cause a funky odor in urine. Beetroot not only affects the smell but also the color of urine, turning it red. Cruciferous vegetables, such as spinach, Brussels sprouts, or Swiss chard, and spices like coriander and cumin, can also lead to unusual urine smells. Puffed wheat, a popular cereal, gives off a distinct malt scent after urination.
If you can smell the sulfuric compounds in post-asparagus urine, there’s nothing to worry about. The smell fades quickly, and the health benefits of this nutrient-dense vegetable outweigh the odd bathroom experience.