A few years ago, scientists raised the flag about a troubling potential source of water pollution: American urine.
Although fad diets are promoting protein intake, Americans are already eating about 40% more than the recommended daily amount. One of the side effects of excess protein is excess nitrogen in the urine. And when this powerful cocktail enters the environment, it can cause toxic algae blooms, destroy ecosystems and make drinking water unsafe, says Maya Almaraz, a Yale University biogeochemist and co-author. 2022 document on the problem. She and her colleagues estimate that overeating protein releases more than 600,000 tons of excess nitrogen into Americans' urine each year.
This is just one of the many surprising things urine can tell you about our health and habits. “If you drink alcohol, there are characteristic molecules in your urine,” says Joshua Kuhn, a professor of chemistry at the University of Wisconsin-Madison. “If you have coffee, we can see it.” Some types of brain tumors even leave telltale signatures in urine before they can be detected by other means, says David Wishart, a professor at the University of Alberta who has pioneered the study of molecules in urine and advocates database of more than 3,000 molecules found in human urine. Advances in basic research show that “there is gold in this golden-colored liquid,” he muses.
What can urine tell you?
Many people have peed in a plastic cup at the doctor's office or on a stick at home. One standard test checks for sugar in the urine to diagnose diabetes. Another notes human chorionic gonadotropin, a marker of pregnancy.
These tests are effective because urine contains metabolites: waste products that are broken down and created into new molecules every day. Just as trash from a home can reveal whether its occupants are vegetarians, metabolites reveal what's going on inside the body. “If there's something wrong in the body, it tends to be concentrated in the urine,” says Wishart.
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Wishart and his colleagues discovered that a panel of 69 metabolites in people's urine could predict who had precancerous colon polyps. In 2020, he and his colleagues published test for 149 different metabolites in urine, with the goal of getting others in the research community to use it to study urine and possibly create new laboratory tests.
Urine isn't good for everything. Stanford genomicist Michael Snyder, who pioneered the use of long-term individual 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 consume. “This is a good opportunity to look at diet and supplements,” Snyder says. Indeed, in one 2019 study From Kuhn's lab, in an effort to see if urine could be used to monitor health in real time, he and his colleagues collected all the urine produced by two volunteers over a 10-day period. They were able to see traces of exercise, traces of certain foods, and even acetaminophen taken the night before—essentially recordings of these people's daily lives.
The toilet of tomorrow
One of the main advantages of urine is that it is easily accessible and is a more convenient way to monitor health than, say, a daily blood draw. “The toilet is really that place,” Kuhn says. He and his colleagues continued to study sensors on toilets that could regularly monitor metabolites in urine, aiding in precision medicine. Such sensors could alert doctors if molecules that were always low in someone's urine suddenly spike, track a person's diet in detail, and provide insight into how they metabolize drugs, for example. “We need to figure out how to measure in the toilet,” Kuhn says. “This is the ideal.”
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Almaraz already knows a lot about what's pouring into Americans' toilets, so she's focused on how to change it. She found that people are often resistant to the idea that they don't need more protein, meaning they continue to deposit 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 that urine can become toxic waste.
“Diets can change. They change all the time,” she says. “I hope we can change them for the better.”
