The Centers for Disease Control and Prevention have a few different ways of measuring obesity in the U.S., including phone surveys, in-home interviews, and physical exams of nationally representative slices of the population.
None of these methods involve poop.
It’s an unsurprising fact, probably, but one that bears noting only because some scientists believe it may soon change—or at least, that it should. In a study recently published in the journal mBio, researchers from the University of Wisconsin and the Marine Biological Laboratory in Woods Hole, Massachusetts, laid out the case for sewage as a public-health tool, arguing that human waste may be a more efficient way of measuring obesity at the population level.
To prove their concept, the authors examined more than 200 sewage samples taken from treatment plants in 71 U.S. cities, using genetic sequencing to identify which bacteria in the mix came from human feces (an average of around 15 percent across the samples). A city, like each of its individual inhabitants, has its own unique microbial signature that tends to stay constant over time; by looking at the bacterial makeup of a city’s sewage, the researchers found, they were able to predict its obesity rate at a accuracy rate between 81 and 89 percent.