Food diaries and nutrition surveys depend on people remembering what they ate, estimating portions accurately and being willing to report foods they may consider unhealthy. A new study suggests municipal wastewater could provide researchers with another source of information.
Scientists analyzed fragments of plant and animal DNA in sewage collected from communities representing about 2.1 million people in North Carolina. The patterns reflected broad differences connected with geography, household income and the proportion of residents born outside the United States. However, the method cannot show how much food people ate, whether their overall diets were healthy or which residents consumed particular foods.
The experimental study, published in the Proceedings of the National Academy of Sciences, used a DNA-sequencing platform called FoodSeq-FLOW. Researchers developed the system to identify dietary DNA that enters municipal wastewater.
“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 senior study author Lawrence A. David, a member of the Duke Microbiome Center and an associate professor of molecular genetics and microbiology at Duke University School of Medicine. “This study helps fill that gap so we can better connect diet to health.”
Researchers collected wastewater from eight treatment plants serving 19 communities in the Charlotte-Mecklenburg, Beaufort-Carteret and Greenville-Pitt regions. Samples were gathered during two periods, from June through December 2020 and again in June 2021.
The team sequenced small fragments of DNA and compared them with genetic reference databases to identify plant and animal species that may have contributed to the samples.
Wastewater serving wealthier communities was more likely to contain DNA from hops, a plant used in brewing beer. Areas with larger foreign-born populations showed more evidence of tropical fruits and beans. Coastal communities had DNA from a wider range of seafood, including drum, Spanish mackerel and triggerfish.
Inland communities appeared to rely on fewer seafood varieties, particularly farmed fish such as Atlantic salmon.
These findings do not establish what individual residents ate. The researchers identified community-level associations, meaning the patterns describe wastewater service areas rather than specific households or demographic groups.
Detecting a food’s DNA also does not reveal its portion size, nutritional value or frequency of consumption. A strong signal could reflect many people eating a small amount, fewer people eating a large amount or food waste entering sinks and drains.
That distinction is important because municipal wastewater contains more than human waste. It may include discarded food and material from restaurants, grocery stores, institutions and other businesses. Different foods may also leave behind DNA at different rates depending on how they are prepared, digested and preserved in wastewater.
The method would not capture residents whose homes use septic systems, and visitors or commuters could contribute to the wastewater without living in the community being studied.
The researchers compared the wastewater findings with dietary DNA detected in 14 stool samples collected in Durham in June 2021. The patterns were similar, offering preliminary support for the method. The small comparison group, however, was not large enough to establish that wastewater can precisely measure community food intake.
The technology is better understood as a potential complement to conventional nutrition research than as a replacement for food surveys.
Dietary surveys can provide details that sewage cannot, including portion sizes, eating frequency, meal preparation and information about the people consuming particular foods. Wastewater may offer a broader and more timely view of community patterns, including people who are often missed by traditional research.
“Wastewater offers an objective way to monitor dietary patterns across entire communities and could help guide more targeted nutrition and food security programs,” said lead study author Mengyi Dong, an associate professor at Virginia Tech’s Seafood Agricultural Research and Extension Center. “Food security isn’t just about whether enough food is available. It’s also about ensuring communities can access healthy, nutritious options.”
Researchers believe the approach could eventually help communities evaluate whether nutrition initiatives are making a measurable difference. For example, wastewater DNA could potentially be tracked before and after a neighborhood receives a grocery store, food assistance program or other intervention intended to improve access to nutritious foods.
That possibility has drawn interest in Durham’s historic Hayti neighborhood, where community leaders have been working to establish a Black-owned, full-service grocery store.
“It would allow us to eat healthier foods more regularly because we wouldn’t have to travel so far to get them,” said Erin Dooley, co-founder of BLK South and a resident of the Grant Street community. “What’s unique about Dr. David’s research is that it’s not just hard facts and data, but it supports our lived experiences.”
The new method cannot yet determine whether opening a store improves diet quality. Researchers would first need to demonstrate that changes in wastewater signals consistently reflect changes in food purchases and consumption rather than food disposal or other activity.
The study also raises questions about how community-level data should be interpreted and communicated. Wastewater samples pool material from large populations and are not designed to identify individuals. Even so, connecting dietary patterns with immigration, income or specific neighborhoods could lead to oversimplified or stigmatizing conclusions if the results are presented without context.
“The result is a snapshot of the community that helps understand where resources are needed,” said study author Rachel T. Noble, a professor of marine sciences at the University of North Carolina at Chapel Hill.
For now, that snapshot remains incomplete. Wastewater DNA may show that traces of certain foods are present, but it cannot provide a complete grocery list, calculate nutrient intake or label a community’s diet as healthy or unhealthy.
The study instead demonstrates that material already collected through public sewage systems may contain useful information about broad dietary patterns. With further validation, it could give nutrition researchers another way to study how food access, culture and geography shape what communities eat.
The study was funded by the National Science Foundation Precision Microbiome Engineering Engineering Research Center, the Chan Zuckerberg Initiative, Schmidt Sciences, the Gerber Foundation, Nature-Springer, the Burroughs Wellcome Fund Pathogenesis of Infectious Disease Award, the Duke Microbiome Center, the Duke Clinical and Translational Science Award and the National Institute of Diabetes and Digestive and Kidney Diseases.