Different Datasets, Different Stories: A Seafood Study Illuminates Blind Spots

Where do people buy their seafood, and what kind of seafood do they eat? Are their decisions influenced by where they live? For decades in the United States, there have been commonly accepted answers to these questions—but one research team had a hunch that these answers might not be the whole picture. So they approached the investigation with a different dataset, learned something new, and breathed new life into the research on seafood consumption.

“People kept telling me that 70 percent of all seafood in the United States is eaten in restaurants,” said Dave Love, an associate scientist at the Johns Hopkins Center for a Livable Future. “But I knew it wasn’t right.”

By 2020, the ubiquitous “70 percent” had become a given, accepted by everyone in the seafood industry, but Love’s skepticism forced him to investigate the source. His investigation led him to a spreadsheet that he was certain no one ever reads, and on one line there was one number indicating the dollar amount of seafood consumed, and from there the “70 percent” was derived.

“I emailed the National Marine Fisheries Service and asked, ‘What’s your math?’” says Love. “They sent me an undated PDF of a document, perhaps from the 1990s.” The National Marine Fishers Service (NMFS), a federal agency that is part of the National Oceanic and Atmospheric Administration, is responsible for the stewardship of national marine resources.

In addition to the data source question, there was the issue of using a dollar amount to determine how much seafood people are eating. An American might spend twice as much to eat salmon in a restaurant compared to eating the same amount at home—so using dollar amounts to figure out how much is eaten at home compared to how much is eaten “out” is problematic.

And then there was the problem of semantics. The word “consumption” means different things to different people. To an economist, “consumption” is a math problem: it refers to how many pounds of seafood are taken into the US food supply, divided by the population. Using that math, it looks like Americans eat about 16 pounds per person of seafood every year. And that “16 pounds” is what journalists use when they report on the topic—but there are some obvious problems with this. Americans may buy 16 pounds of seafood, but that doesn’t mean they’re eating 16 pounds. First, Americans throw away a lot of seafood, mostly because they’re afraid of spoilage. Second, as Love says, “The supply data is the raw weight of what you buy at the grocery store. But what we eat is cooked.” After you cook the fish, the weight decreases.

But many cling to the “16 pounds” and use that number to measure progress towards dietary recommendations, which, according to Love, is a problem.

The team wanted to measure “consumption” from restaurants and grocery stores in a way that reflected what Americans are actually eating, as opposed to the dollars being spent. A couple years ago, Love and the team sat down with a group of experts and brainstormed all the datasets they could use to get a better picture of this number.

“We came at it from a lot of different disciplines,” says Love. “And I learned that NHANES—which is well known to public health folks—was not on anyone’s radar in the seafood sector. I think they just didn’t know about it.”

NHANES, the National Health and Nutrition Examination Survey, is a major program of the CDC that surveys 6,000 people in a nationally representative sample and includes demographic, socioeconomic, dietary, and health-related questions. After combining the NHANES data with other, traditional sources, the authors found a few surprises.

The authors say that a truer number that reflects the edible portion and cooked weight of how much seafood Americans eat every year is 11.7 pounds per person. The study also confirms that Americans eat more seafood “away from home” than they do other types of food, but only if you’re measuring by money spent. If, however, you measure by the volume of cooked seafood eaten, Americans are eating more at home.

“It gave us a new picture of what people eat,” says Love. “Fisheries people and marine biologists had not previously thought to look at NHANES data.”

The idea to use NHANES instead of NMFS data has sparked new ideas in the seafood research world. Frank Asche, a professor at the University of Florida’s Food Systems Institute, has been arguing for new perspectives, and this paper is helping him to change how researchers and policymakers are thinking about seafood.

“It is really important to expel myths like the 70 percent, because they create barriers for figuring out what is really going on,” says Asche. “This paper gives us a new start.”

Love argues that simply looking at consumption doesn’t answer enough questions that we need answered in order to make good policy. We can also look at supply chains and ask where do people buy seafood? How does price factor into their decisions? Are people with lower incomes eating less seafood? Different species? We should be looking at all of that and trying to correct our blind spots, he says.

What the scientists learned from the research, “Food Sources and Expenditures for Seafood in the United States,” published in June 2020 in Nutrients, changed our understanding of the percentages, but it’s mostly consistent with what we’ve understood about Americans’ seafood eating patterns, mainly that most Americans do not eat enough of it to meet the recommendations for seafood outlined in the Dietary Guidelines for Americans 2015–2020.

But there’s so much more to learn, particularly with regard to who’s eating the least seafood. To create effective interventions, we need to understand what affects those decisions. Love and team are teeing up the next studies.

Illustration by Mike Milli, 2020.