When we talk about the environmental impact of food, we often categorize foods on a large scale, perhaps by diet type (vegetarian, pescatarian, vegan, etc) or macronutrient. Reality is more complicated. Food has many subtleties and variables that can determine a diet’s impact. A recent paper, published in May 2021 by Walker et al., examined some of those subtleties, like seasonality and location, to measure the climate change and biodiversity impacts of diets in different cultures and countries in hopes of updating and bringing nuance to recommendations for low impact diets. “Results indicate that, although optimized diets are similar, there are marked differences in the detailed composition depending on country, season, and impact considered.”

The study utilized the McCance and Widdowson’s Composition of Foods Database as the foundation for developing the country and season-specific metrics. Next, the authors collected or calculated the other considerations in their model, such as seasonal crop production by country, food production impacts, climate change impact calculations, and land-based biodiversity loss impact calculations. Transport and trade were key considerations as well, separating the analysis from many previous diet impact studies.

While the paper focused primarily on the results of specific comparative scenarios (recommended diets in Switzerland vs. Spain, or August vs. February, for example), the authors also produced an optimization tool software to generate personalized diet recommendations based on impact priorities. This led to some very practical insights. For example, Swiss people consume more dairy, so the recommended diet for Switzerland includes more dairy. Grocery shopping considerations and cultural tendencies were actually woven into the results, making this paper unique to its field.

From the seafood category, only herring and mackerel, which would rank as some of the most efficient foods in terms of greenhouse gas emissions per gram of edible protein, were considered. These forage fish species were, “found to be vital to balancing both health and impacts.” Dietary supplements were included in the recommendations, however, “without supplementation, the lowest impact diet that meets all nutritional needs is not vegetarian or vegan, but rather one which contains considerable amounts of fish.” The vitamin D and omega-3s in these fish were, “specific nutrients not readily available from other food items.” This finding illustrated the essential nutritional role seafood plays in places without access to specific dietary supplements.

Unfortunately, the practicality for seafood dietary recommendations were limited in this study’s analysis. Herring and mackerel are not particularly prominent seafood species, even in the European diets they compared from Spain and Switzerland. The authors aimed to develop a tool to inform optimized diets for “any global geographical location and seasons,” but the omission of other seafood species in this project was puzzling.

Previous studies by Hilborn et al. (2018) and Koehn (2020) showed the wide range of potential impact indicators for different fisheries and seafood farms. The only mention of these considerations was that the “inclusion of other environmental impact indicators that better capture the impacts of fish consumption (i.e., marine biodiversity loss, seabed damage) would likely shift diets toward farmed fish or supplements. Similarly, the high land use related biodiversity loss impacts for the fish in this analysis may be unfounded if wild caught.”

This was not a fishery or seafood-focused study, so these areas for further research are understandable and do not detract from the value of the tools created. I would be curious to know if the study began as a comparative look at vegetarian, vegan, and omnivorous diets with only land-based foods considered, but then pivoted to include herring and mackerel when the authors realized seafood was a key missing piece in prescribing an optimized diet. The results can be counted as another volume in the growing archive of support for seafood-inclusive diets. “Ultimately the most effective way to consume a low impact diet was not vegetarian or vegan, but rather one that contained specific types of fish and/or supplements.”