Nutrient Density to Climate Impact index is an inappropriate system for ranking beverages in order of climate impact per nutritional value

A recent paper published in Food & Nutrition Research contributes to the important research area of how to achieve nutritional goals while reducing the amount of greenhouse gas (GHG) emissions from the food system (1). The paper introduced a novel method of measuring the nutrient density of a food or drink in comparison to GHG emissions associated with the production, manufacturing, packaging, and transportation of that food or drink, using a life-cycle perspective an index called Nutrient Density to Climate Impact (NDCI). The authors of the paper used the NDCI index to compare eight beverages: milk, soft drink, orange juice, beer, wine, bottled carbonated water, soy drink, and oat drink. The NDCI index for milk was higher than for the other beverages, and the authors concluded that ‘milk both has the highest nutrient density per se, and has the highest nutrient density in relation to GHG emissions of the compared beverages. We also conclude that the NDCI index is a tool that facilitates inclusion of a nutritional aspect of the climate debate.’ We are concerned that the NDCI index is flawed, as the ranking of the beverages produced by the index is dependent on an arbitrary choice of threshold for contributing to the Nordic Nutrition Recommendations (NNR). The NDCI index is calculated as follows: