People looking for a diet that is healthy and climate-friendly may want to consider eating more oysters and herring.
When it comes to greenhouse gas emissions, plant-based foods are generally touted as the low-impact alternative to red meat. But a new study found that certain types of shellfish, including farmed shellfish and small, fatty fish like herring, are more climate-friendly than even some vegetables when nutritional content is taken into account. However, other seafood, including farmed shrimp, fared worse than beef.
“I wanted to compare types of shellfish in terms of not only their emissions, but also how healthy they are compared to other food groups,” said Zachary Koehn, lead author of the study. “I wanted to see how seafood compared to all the different land-based production systems.”
Now an early career partner in Stanford Center for Ocean Solutions, Koehn compared the life cycle greenhouse gas emissions of different staple foods by considering how well those foods met certain dietary requirements. He completed the role, posted on tuesday in Environmental Research Letters, while pursuing his Ph.D. with co-authors Edward H. Allison and Ray Hilborn at the University of Washington. Christopher Golden of Harvard University was also an author.
Each food received a value based on the greenhouse gas emissions needed to meet nutritional requirements measured as an average of 12 nutrients that are critical for child health and development, Koehn said. Top scores across all food groups were good-for-you root vegetables like carrots, parsnips, and turnips, and small pelagic fish like sardines and anchovies, as well as farmed mussels, clams, and oysters. All can be produced or harvested in relatively low-impact ways while providing nutrient density, according to the paper.
The worst scores were farmed catfish, tilapia and shrimp, due to their relatively low nutritional value and higher emissions, beating even beef, because it is more nutritious despite the fact that producing it generates high emissions.
Koehn pooled previous studies to compare global staple foods, such as imported farmed seafood from Asia and fattened beef, versus grass-fed beef, in the analysis.
Farmed shellfish like oysters and mussels can have a very low footprint because they absorb carbon dioxide and don’t need to be fed. Small pelagic fish are caught with a purse seine, a type of net that consumes less fuel because it does not drag the bottom. On the other hand, farmed shrimp are often caught with fuel-intensive trawlers.
The paper is part of a new area of research that should be commended for looking at the climate impact of food not by comparing a pound of apples to a pound of chicken, but also by examining their relative nutritional value, said Peter Tyedmers, a professor at the School of Resources and Environmental Studies at Dalhousie University in Halifax, Nova Scotia.
“They are contributing to this next important food systems analysis space where we look beyond single foods to combinations of foods in diets,” said Tyedmers, who created his own seafood carbon emissions tool and has been an advisor to the Monterey Bay Aquarium’s Shellfish Watch program.
However, Tyedmers cautioned that mining data on food life-cycle assessments, a way of measuring environmental impact that is supposed to take into account everything that goes into producing a pound of potatoes, a lettuce or a salmon fillet , from multiple studies can be problematic because methods vary.
Koehn said he re-run the numbers on the study to make sure the life cycle assessments were consistent to the best of his knowledge.
“I recognize that future studies should look at that much more deeply,” he said.
Both Koehn and Tyedmers say seafood is often dismissed in food policy discussions because it is so complicated, with varying degrees of sustainability for farmed and wild-caught, and imported and domestic seafood. But that overlooks the fact that many types of seafood hold promise to feed a growing world population with less climate impact than other foods.
“There is increasing recognition that many types of shellfish are highly nutritious,” Koehn said. However, they are “often left out of the politics of food systems,” such as the federal farm bill and the food stamp system and school lunch programs. Koehn said he believes that’s partly because wild-caught seafood is regulated by the Commerce Department and not the Agriculture Department, which oversees those programs.
Other research comparing the environmental impact of seafood and land foods focuses on their protein content, however Koehn felt it was important to consider a broader range of nutrients, so he based his nutritional analysis on omega-3 fatty acids , vitamin B12, iron, zinc and other micronutrients.
Not many people are willing to eat herring or even oysters, at least as a major part of their diets, although canned sardines and the anchovies are back during the pandemic. Koehn said more work needs to be done on the culinary side to make such food acceptable to the general public.
“It’s really important if we’re going to think about a food system that’s more sustainable and more nutritious,” he said. “We really need to think about all the options on the table.”
Tara Duggan is a staff writer for the San Francisco Chronicle. Email: [email protected] Twitter: @taraduggan
