Scientists Turn Sewage Into A Real-Time Nutrition Tracker

Wastewater DNA Can Reveal a Community’s Food Culture and Economic Patterns

A city’s sewage carries more than waste. It carries clues about what a community eats, its cultural makeup and its economic circumstances. Researchers scanning wastewater from 21 North Carolina communities found that food DNA tracked cultural roots, economic profile and even distance from the coast. The method examines pooled wastewater from entire service areas, not individual households.

Scientists at Duke University and the University of North Carolina at Chapel Hill built a tool called FoodSeq-FLOW that scans municipal wastewater for tiny fragments of food DNA, according to findings published in the Proceedings of the National Academy of Sciences. Sequencing genetic material left behind from digestion let the team estimate which foods were appearing in a community’s diet, without a survey.

Traditional government surveys ask a few thousand Americans to recall what they ate over the past day or two, a method plagued by faulty memories and shrinking response rates. Sewage plants already collect wastewater for testing, and the research team added a DNA-sequencing workflow, tracking population-wide eating habits at a cost of less than one penny per person.

Poor diet is a leading driver of chronic disease worldwide, and researchers say the tool could help spot problems faster than traditional surveys allow. “Poor diet is one of the world’s biggest drivers of chronic disease, but we’ve never had a fast objective way to measure what people eat,” said Lawrence A. David, senior study author and a member of the Duke Microbiome Center, according to a Duke news release. “This study helps fill that gap so we can better connect diet to health.”

Wastewater DNA Broadly Matched Food Signals Found in Stool Samples

Led by Duke microbiologist Mengyi Dong and colleagues, the team collected 183 wastewater samples from 21 treatment plants serving roughly 2.1 million North Carolina residents from 2020 to 2021. A single sample can represent hundreds of thousands of residents, since plants process wastewater from entire cities and counties.

Scientists targeted two genetic markers that survive digestion: a plant gene called trnL, found in chloroplasts, and an animal gene called 12SV5, found in mitochondria. Using a process similar to a coronavirus test, but tuned to detect food, the team sequenced these fragments and matched them against a reference database of known foods.

Comparing wastewater samples from Durham with stool samples from 14 Durham residents during the same month, researchers found the two data sets shared 96 types of plant DNA, with a meaningful correlation, according to the study. Nearly 99 percent of animal DNA reads and about three-quarters of plant DNA reads matched species recognized as human foods, not stray pollen or yard waste washed into the sewer system.

Seasonal patterns reinforced confidence in the tool: fruits and vegetables tracked North Carolina’s harvest calendar, and turkey peaked around the November and December holidays.

Wastewater Food Signals Tracked Communities’ Cultural Makeup

Comparing dietary signatures across communities with different income levels, education rates and immigrant populations, drawn from census data, researchers found that service areas with larger foreign-born and Asian populations showed a distinct pulse of mung beans, chickpeas, mangoes and coconut, ingredients tied to South Asian cooking but not native to North Carolina. Those same ingredients were strongly associated with higher community income, while North Carolina staples like collard-family cabbage leaned toward lower-income areas. A statistical test found the association was unlikely to be explained by random variation, though the study cannot show that income or immigration caused the differences.

Rural, less metropolitan areas leaned toward celery, onion and black-eyed peas, foods commonly associated with Southern cooking.

Coastal Communities Showed Distinct Local Seafood Signatures

Wastewater DNA also picked up a geographic divide in seafood. Coastal and rural communities showed heavier traces of local fish like drum and Spanish mackerel, while inland cities relied more on nationally distributed, farmed species like Atlantic salmon and tilapia. Distance from the coast statistically predicted which seafood showed up in a community’s sewage, suggesting supply chains shape what ends up on a plate as much as taste does.

“Could we be doing more to support local fisheries and make their seafood more available? It looks like we certainly could,” said Rachel T. Noble, a marine sciences professor at UNC-Chapel Hill and one of the study’s authors, according to a Duke news release.

Hops, Barley and Kratom Were More Common in Higher-Income Service Areas

A second and unexpected pattern emerged alongside the cultural and geographic findings. Communities with higher per capita income and food spending showed elevated levels of hops and barley, the two main ingredients in beer, along with kratom, a plant-derived product sometimes used as an opioid alternative and legally available in North Carolina. A separate model identified hops, barley and kratom as the strongest positive food-DNA predictors of per capita income among the plants analyzed.

That finding runs counter to stereotypes linking alcohol and psychoactive substance use with financial hardship. One possible explanation is that these products reflect discretionary spending. But the wastewater data cannot show who bought them or whether some of the signal came from nearby breweries rather than home consumption.

Sewage was never designed to reveal where certain foods and products are more common, but wastewater DNA testing turns out to be a candid narrator of culture, geography, class and public health risk. Those networks expanded during the pandemic to track viral outbreaks, and the same infrastructure could support broader dietary monitoring, though communities would still need lab equipment and further validation first. In this study, the analysis cost less than one cent per person.

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Disclaimer: This article describes patterns found across pooled community wastewater samples, not information about any individual person or household. The findings show associations between food DNA and community-level income, education and demographic measures, not proof that income or immigration directly caused the dietary differences observed. Wastewater DNA testing measures relative abundance, not exact amounts of food eaten, and results from North Carolina may not apply the same way to other regions.