The science of sustainable seafood, explained

The climate change impacts of nutrition

Though large-scale climate change mitigation policies are needed to make meaningful progress, food choices are one of the most effective ways individuals can reduce their carbon footprint. I like to choose healthy, delicious food with low environmental impact. You probably do too.

The best food choices often involve substituting a low-impact protein for a high-impact one, as protein is the most resource-intense macronutrient. Seafood is generally a low-impact choice, but until recently, data has been limited on how different kinds of seafood compare in their environmental impacts and their nutrition profiles. A paper from last year, Hilborn et al. 2018, measured overall environmental impacts of different types of seafood by compiling 148 life cycle assessments (LCAs), a “cradle to grave” analysis that accounts for every aspect of a food product’s resource use. Along with another study that compiled LCAs of land-based food, people now have a good sense of individual foods’ environmental impact.

Missing, however, has been discussion beyond macronutrients into the overall nutrition profile of seafood, i.e., how healthy a seafood product is relative to its environmental impact. A new, open access study in the Journal of Cleaner Production does just that; it compares the nutrient profile to greenhouse gas (GHG) emissions for several different kinds consumed in Sweden.

Researchers, led by Elinor Hallström of Research Institutes of Sweden (RISE), compiled LCAs of 37 common seafood products consumed in Sweden (though produced all over the world) to rank the GHG emissions of those products in comparison to their ‘nutrient density score,’ a quantitative measure of how healthy a food product is.

So what seafood should Swedes eat?

Before I show the results, I want to acknowledge that the study is Sweden-specific and only covers 37 seafood products common to that country. Many of the conclusions it draws are applicable to other parts of world, but some are not. More on this later.

Below is a figure from the paper that plots the 37 types of seafood on a graph with one axis representing climate change impact (GHG emissions) and the other nutrition. The cross section in the middle is the median of all seafood products studied; Beef (B), Pork (P), Chicken (C), and Eggs (E), are plotted as well for comparison. The size of the circle represents the amount consumed in Sweden.

Figure from Hallstrom et al. 2019 showing nutrient density and climate change impact of different foods
Combined nutrient density and climate impact of seafoods analyzed. Log transformed data scaled around average representing the median of all seafoods. Bubble size reflects Swedish consumption rates from Ziegler and Bergman (2017) on a continuous scale, i.e. each bubble has its own size. B = beef, P = pork, C = chicken, E = egg. From Hallström et al. 2019.

Seafood in the bottom right quadrant are the best to eat for both health and climate impact, it includes European sprat, Atlantic mackerel, Atlantic herring, pink salmon, and Alaskan pollock. Seafood in the upper left quadrant are some of the poorest choices, providing relatively little nutrition, but incurring high GHG costs; these include farmed catfish, Norway lobster, Northern prawn, and Scallops.

This is an excellent guide to decide what to eat for dinner! The only thing missing from a figure like the above is stock sustainability. For example, the small grey circle with the second highest nutritional score and slightly below average GHG emissions seems to be a great choice, but it’s European eel, a critically endangered species. The authors acknowledged this shortcoming in the paper and provided a list of all 37 seafood products ranked by nutrition, GHG, and a combined score with ‘avoid’ species (as defined by WWF) highlighted in orange.

Table ranking seafood by nutrition and climate change impact
Orange/pink cells indicate species classified as ‘avoid’ in the Swedish WWF consumer guide (WWF, 2018) due to unsustainable production practices (the dominant source on the Swedish market). Grey cells indicate species for which consumption is recommended to be limited due to potential content of toxic compounds (SFA, 2018a) and/or levels of nutrients exceeding upper daily recommended intake levels (NCM, 2014). Brown cells have both sustainability and health concerns, white cells have neither. From Hallström et al. 2019.

The average seafood product is much more nutritious than its land-based alternatives (egg, chicken, pork, beef). 24 of the 37 seafood products in the study rank higher than the most nutritious alternative protein, egg. Though egg and chicken are in the upper half of climate-friendly protein, most seafood eaten in Sweden is much better for the planet than pork or (especially) beef. Using a combined nutrition/climate metric, 21 of 37 seafood products perform better than chicken, the highest rated land-based protein outside of egg.

With such a small, specific sample of seafood, some surprising results should be expected. One that stands out is farmed oysters, which received the highest nutritional score (unsurprising), but also one of the worst GHG scores (very surprising). Farmed bivalves are generally considered the lowest-impact seafood to eat—data from Hilborn et al. 2018, shows them to be lower-impact than many plant-based foods, so seeing farmed oysters scored so low seems odd. The authors acknowledge the strange finding and explain it as a function of only using one farmed oyster LCA from a particularly high-impact farm in Scotland. Dr. Friderike Ziegler explains, “for oysters, there is only one published LCA study, from a Scottish oyster farm that presents higher climate emissions than unpublished data from larger-scale farming operations in Washington State. The lack of data for some species leads to uncertainty and results with regard to GHGs could change as more data becomes available.”

Large-scale vs individual climate change action

A study like Hallström et al. 2019 empowers consumers to make better individual choices about the food they eat, e.g. I will definitely think about the nutrition to impact ratio next time I am at the grocery store. Indeed, individual action and choice plays an important social and psychological role for many people concerned about climate change, but meaningful, large-scale mitigation will come from collective action to elect and pressure decision-makers to enact systemic change… And this paper is great example of that, too:

This paper came about because Sweden’s decision-makers decided to update the country’s food recommendation guide to include environmental impacts. How cool is that—actual systemic change!

We need governments to lead the fight against climate change; funding research (Sweden funded Hallström et al. 2019) and updating food recommendations to include environmental impacts is a great example of meaningful systemic change that also empowers individual citizens—the perfect civic action.

Picture of Max Mossler

Max Mossler

Max is the managing editor at Sustainable Fisheries UW.

We have written a lot about the environmental/climate change impacts of food.

Check out some of our other stories below:

Eating Plants & Seafood

Conscious eating can and should include several different kinds of food. A plant-based diet has lower impact relative to a standard diet that includes lots of animal protein, but a diet that includes fish can have as low, or even lower impact.

Read More »

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