A few years ago, scientists raised the alarm about a worrying potential source of water pollution: American urine.
Although fad diets emphasize protein, Americans already consume about 40 percent more than the recommended daily amount. A side effect of excess protein is excess nitrogen in the urine. And when this powerful cocktail enters the environment, it can cause toxic algae blooms, disrupt ecosystems and make drinking water unsafe, says Maya Almaraz, a biogeochemist at Yale University who co-authored a 2022 paper on the problem. She and her colleagues calculated that, thanks to excessive protein consumption, more than 600,000 tons of excess nitrogen are excreted in Americans’ urine each year.
This is just one example of the many surprising insights that urine can reveal about our health and habits. “If you consume alcohol, there are signature molecules in the urine,” says Joshua Coon, a chemistry professor at the University of Wisconsin-Madison. “If you have a coffee, we can see a signature from it.” Some types of brain tumors even leave telltale traces in urine before they can be discovered by other means, says David Wishart, a professor at the University of Alberta who pioneered the study of molecules in urine and maintains a database of more than 3,000 molecules found in human urine. Advances in fundamental research reveal that “there is gold,” he muses, “in this golden fluid.”
What can urine tell us?
Many people have peed in a plastic cup at the doctor’s office or on a stick at home. A standard test looks for sugar in urine to diagnose diabetes. Another reports human chorionic gonadotropin, a pregnancy marker.
These tests work because urine contains metabolites: waste products from the daily activity of breaking down and forming new molecules. Just as the waste from a house can reveal, for example, whether the inhabitants are vegetarian, metabolites reveal what is happening inside the body. “If there’s something wrong in the body, it tends to concentrate in the urine,” says Wishart.
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Wishart and colleagues found that a panel of 69 metabolites found in people’s urine could predict who had precancerous polyps in their colon. In 2020, he and his collaborators published a test for 149 different metabolites in urine, with the goal that others in the research community would use it to study urine and potentially create new laboratory tests.
Urine is not useful for everything. Stanford genomicist Michael Snyder, a pioneer in the use of long-term personal health monitoring, says urine is not as good an indicator as blood when it comes to many tissues, including muscle and heart tissue.
However, it can provide particularly detailed information about what people ingest. “It’s a good window into diet and supplements,” Snyder says. Indeed, in a 2019 study by Coon’s lab to determine whether urine could be used for real-time health monitoring, he and his colleagues collected all the urine produced by two volunteers over 10 days. They were able to see traces of exercise, traces of particular foods and even acetaminophen taken the night before, which is essentially a record of these people’s daily lives.
The toilets of tomorrow
One of the main advantages of urine is that it is easily available and is a more convenient way to monitor health than, for example, daily blood tests. “The restroom is definitely the place to be,” Coon says. He and his colleagues continued to explore toilet-based sensors that could routinely track metabolites in urine, contributing to precision medicine. Such sensors could alert doctors if a molecule that has historically been rare in a person’s urine suddenly spikes, monitor a person’s diet in detail and provide insight into how they metabolize medications, for example. “We have to figure out how to take measurements in the toilet,” says Coon. “It’s ideal.”
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Almaraz already knows a lot about what goes on in American bathrooms. So she’s focused on how to change that. She found that people are often unreceptive to the idea that they don’t need more protein, which means they continue to release too much nitrogen into the environment. That’s why she wants to help people understand the consequences of seemingly personal choices like diet and raise awareness of the fact that urine can turn into toxic waste.
“Diets can change. They change all the time,” she says. “I hope we can change them for the better.”
