What do people eat? Plant and animal DNA in sewage provide clues
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How can sewage DNA reveal what a community eats?
Hey, it's Flora, and you're listening to Science Friday. Imagine you wanted to get an idea of what people are eating in a given community. You could look at grocery store sales, but that doesn't capture everyone and everything they ate. You could do surveys, but not everyone will respond. And if they do, maybe they don't remember exactly what they ate, or they'll selectively block out that sleeve of Entenmann's chocolate-frosted doughnuts. And if they don't, So my next guest is working on another way of tracking community nutrition from a back-end data source, sewer water. Dr. Lawrence David uses genetic data to study nutrition, and his research group came up with this innovative, if maybe a little bit gross, technique to analyze the DNA in sewage to identify what plants and animals people are eating.
He's calling his research project the Edible Atlas. Lawrence, welcome to Science Friday.
Hi, nice to be here.
Thanks for being here. Tell us right off the bat what foods show up. I mean, what are you finding?
Oh, you see everything.
What foods and species are detectable in wastewater samples?
Things like rice, bananas, wheat, soybeans, a lot of the really common foods. And then we see a lot of things that you wouldn't necessarily think we eat a lot of, like spices and herbs. So like rosemary and sage or garlic and ginger. So we see almost everything, it seems.
How granular can you get? Do you get fish or can you get catfish?
We can see all kinds of different fish, and it depends on how genetically related they are. We see maybe 50 different species of fish. It's many more than I thought we ever could. But on the other hand, some plants that are genetically very similar, we actually have a hard time telling apart. So things like broccoli, cauliflower, things that are closely related actually kind of look the same to us.
Do all foods show up equally as well in the data?
That's a good question. Some things, depending on how we prepare them, don't always show up. So the thing that comes to mind is coffee.
How precisely can you distinguish between related plants and animals in sewage DNA?
Coffee doesn't seem to turn up as much as at least I know I'm doing my part to put it into the wastewater and we're not seeing it. But tea shows up pretty well. And I think that might have to do with how when you steep tea, you're actually drinking a little bit of those leaves.
I have to say, I'm surprised that DNA can survive my stomach and intestines and the sewer. Is it a hardy molecule? I mean, how much of that DNA is surviving?
Yeah, DNA is hardier than you might think. So our digestion, though, is pretty efficient. We estimate that probably about 99% of the DNA that we eat gets digested and broken down. The thing is that we eat a lot of it. So... We estimate that people are eating maybe up to a gram of DNA a day, so billions of copies of the genes that we sequence. And so even if 99% are degraded, there are still millions of copies per person that can be ultimately amplified out and sequenced. And also, when we go back, anthropologists have done this and archaeologists, you can get DNA from poop samples that go back hundreds of years, sometimes further than that. So DNA can really stick around.
Which foods fail to show up reliably and why?
That's interesting. Okay, walk me through the logistics for how you do these experiments. Like, what should I picture?
Depending on where you're sampling, someone might go, say, to a wastewater treatment plant. Right as the sewage is entering, someone will scoop out some of that wastewater.
When you say some of that, gallons, a teaspoon?
Yeah.
liters, so a decent amount. You can do it two different ways. You can scoop out liters or suck out liters of fluid. You can do it all at once, or you can do it over the course of, say, 24 hours. And the other way you do it is that you kind of lower down something very absorbent, and that sort of sucks up material and DNA.
Is the wastewater treatment plant on board, or can you just sort of like pop open a manhole cover and do this?
Yeah.
You can do both.
How much dietary DNA survives digestion and sewer travel to be sequenced?
You should probably ask for permission if you're going to do either of those things, which we generally do. But yeah, I think that we've been really delighted with how open and helpful a lot of people who work with wastewater have been in letting us take a peek.
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Chapters
8 chapters
1
How can sewage DNA reveal what a community eats?
0:02–1:10
2
What foods and species are detectable in wastewater samples?
1:10–2:15
3
How precisely can you distinguish between related plants and animals in sewage DNA?
2:15–3:36
4
Which foods fail to show up reliably and why?
3:36–4:31
5
How much dietary DNA survives digestion and sewer travel to be sequenced?
4:31–5:51
6
What are the practical steps and sampling methods used to collect sewage for analysis?
5:51–9:06
7
What ethical and privacy concerns arise from analyzing community sewage?
9:06–10:42
8
How did the researcher’s personal experience shape the Edible Atlas project?
10:42–12:22
Speakers
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