A handful of years ago, scientists raised the flag about a troubling potential source of water pollution: American urine.

Although trendy diets push protein, Americans already eat around 40% more than the daily recommended amount. One side effect of excess protein is extra nitrogen in urine. And when that potent cocktail makes it into the environment, it can cause toxic algal 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 overeating protein, more than 600,000 tons of excess nitrogen come out in Americans’ urine each year.

That’s just one example of the many surprising insights urine can reveal about our health and habits. “If

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