Optimizing Norwegian diets to meet NNR2023 and reduce environmental impact

Promoting increased compliance with national dietary recommendations is one plausible step towards realizing sustainable diet patterns in Norway, especially if these recommendations integrate NNR2023.

Background: Further knowledge of potential benefits and challenges linked to diets following the new Nordic Nutrition Recommendations (NNR2023) is critical to the development of revised food-based dietary guidelines for Norway. In the present paper, we aim to examine NNR2023 from a Norwegian perspective by: 1) investigating the environmental impacts of nutritionally optimized diets following NNR2023, 2) measuring differences in potential for environmental impact reduction across scenarios of meat consumption, and 3) identifying nutritional challenges.
Methods: A series of optimizations were run to optimize the Norwegian diet in terms of nutrition, health, and environmental sustainability. A quadratic programming model was used with an objective function of minimizing departure from the average observed diet of Norwegian adults (baseline diet), based on the national dietary surveillance survey Norkost 3 (n=1,787; 2010-2011). Nutrient and health constraints were derived from NNR2023. Environmental impacts (global warming potential, freshwater and marine eutrophication, terrestrial acidification, water use, and land use) were estimated according to a database of environmental impact data representative of the Norwegian market. First, the observed diet was optimized to meet requirements for nutritional adequacy, health, and acceptability. Then, stepwise global warming potential constraints were applied at 5% intervals, until no feasible solution was identifiable.
Results: Optimizing the baseline diet to meet nutrient and health constraints alone resulted in a modest decrease in climate impact. If additional constraints were applied to maintain intake of ruminant meat at baseline level, optimization of the diet to follow nutrient and health constraints did not reduce climate impact compared to baseline. The model including environmental constraints identified diets that met nutrient, health, and acceptability constraints, and reduced dietary climate impact up to 35% compared to baseline. The greatest reduction in climate impact was achievable when a daily portion of legumes was imposed as a hard constraint. Diets with lower legume content were also identified and reduced climate impact up to 30% compared to baseline. Reductions in climate impact were achievable while maintaining intake of ruminant meat at baseline level, though feasible solutions were not identified beyond a 15% reduction in climate impact.
Conclusions: Adjusting Norwegian diets to follow NNR2023 guidelines may simultaneously result in environmental benefits, which is in line with NNR2023’s mandate to consider environmental factors in guideline development. However, the potential for further reductions in environmental impact is dependent on distribution of meat consumption in the diet.