Scientists Predict Obesity Rates by Examining Sewage Microbes

The microbial makeup of a city’s sewage can indicate its population’s physique

test tube
Sigrid Gombert/Westend61/Corbis

America’s cities are a diverse bunch, each one with its own distinct landscapes, history, culture—and sewage. According to a new study, we can learn quite a lot about a city by examining its fecal sludge. 

After collecting and analyzing sewage from wastewater treatment plants in 71 cities across the country, a team of University of Wisconsin-Milwaukee researchers discovered they could use the samples to predict, with 81 to 89 percent accuracy, whether the sewage sample came from a relatively lean population or population with a higher obesity rate.

While past research has shown that lean and obese individuals house different sets of microbes in their guts, “this is the first to demonstrate that those microbial differences also play out across entire populations, even after our poop gets flushed, mixed together, and sent through miles of pipes,” Mother Jones reports.

The gut microbiomes of lean and obese people differ in two ways—both in the type and in the diveristy of the microbes. From Scientific American:

In studies of twins who were both lean or both obese, researchers found that the gut community in lean people was like a rain forest brimming with many species but that the community in obese people was less diverse – more like a nutrient-overloaded pond where relatively few species dominate. Lean individuals, for example, tended to have a wider variety of Bacteroidetes, a large tribe of microbes that specialize in breaking down bulky plant starches and fibers into shorter molecules that the body can use as an energy source.

The differences in our gut microbiomes depend, to some extent, on how we were born and what we were first fed: studies show that infants born by cesarean section or fed formula do not develop the same diversity of microbes in their guts as infants born vaginally or fed breast milk. But microbial differences can also develop based on what we ingest later in life: processed foods and antibiotics are both linked to less diverse gut microbiomes.

The new study has implications beyond deciphering obesity rates. Scientists are only beginning to understand the importance of gut microbiomes to overall human health; having a relatively inexpensive, anonymous way to study people’s poop could be important in furthering this research. Here’s hoping the researchers remember their gloves! 

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