Greenhouse Gas Emission Estimates of U.S. Dietary Choices and Food Loss

The paper finds the following:

1. Food loss is a key contributor to emissions, with 1.4 kg of carbon dioxide equivalents to the overall carbon footprint of the average U.S. diet.  By eliminating food waste the study estimates that food related emissions could be reduced by nearly 30% (assuming that the wasted food would not otherwise be produced).

2. It also finds that in the current US diet, meat – and specifically beef – contributes disproportionately to its overall GHG impacts.  Although beef accounts for only 4% of the retail food supply by weight, it represents 36% of diet-related GHG emissions.

3. However, a shift in dietary patterns towards those recommended in the “2010 Dietary Guidelines for Americans” would not lead to a reduction in emissions, but rather an increase.  If Americans adopted the recommendations in USDA's current guidelines while keeping caloric intake constant, diet-related greenhouse gas emissions would increase 12 percent. This is mainly because although meat consumption would decrease– this change is compensated for by an increase in dairy intakes, in line with recommendations. 

4.  The study also finds that a shift towards a lacto-ovo-vegetarian diet would lead to an approximate 30% reduction in emissions, roughly equivalent to that achieved by eliminating food waste.  NOTE: the lacto-ovo-vegetarian diet specified in the study is not that consumed by ‘typical’ US vegetarians, but the ‘ideal’ vegetarian diet specified in the USDA dietary guidelines for vegetarians.  Further details are provided in the Table S3 in the supporting information document that accompanies the paper itself.

The authors conclude that actions to shift diets and reduce food waste represent an  economically effective GHG  mitigation option, requiring collaboration among government, business and consumers - but also emphasise the need to incorporate environmental considerations into current dietary advice.

Abstract

Dietary behavioral choices have a strong effect on the environmental impact associated with the food system. Here, we consider the greenhouse gas (GHG) emissions associated with production of food that is lost at the retail and consumer level, as well as the potential effects on GHG emissions of a shift to dietary recommendations. Calculations are based on the U.S. Department of Agriculture's (USDA) food availability data set and literature meta-analysis of emission factors for various food types. Food losses contribute 1.4 kilograms (kg) carbon dioxide equivalents (CO2-eq) capita−1day−1 (28%) to the overall carbon footprint of the average U.S. diet; in total, this is equivalent to the emissions of 33 million average passenger vehicles annually. Whereas beef accounts for only 4% of the retail food supply by weight, it represents 36% of the diet-related GHG emissions. An iso-caloric shift from the current average U.S. diet to USDA dietary recommendations could result in a 12% increase in diet-related GHG emissions, whereas a shift that includes a decrease in caloric intake, based on the needs of the population (assuming moderate activity), results in a small (1%) decrease in diet-related GHG emissions. These findings emphasize the need to consider environmental costs of food production in formulating recommended food patterns.

Citation

Heller, M. C., Keoleian, G. A., 2014, Greenhouse Gas Emission Estimates of U.S. Dietary Choices and Food Loss, Journal of Industrial Ecology, doi: 10.1111/jiec.12174

The paper is available open access and can be downloaded here.  A paper by Vieux et al also concludes that ‘high nutritional quality’ diets are not necessarily more sustainable – you can access the paper and read the FCRN’s commentary  here. 

Read more about dietary recommendations here and environmental impacts and GHG emissions related to food waste here. Further resources on greenhouse gas emissions from different diets can also be found on our website, by searching in our research library for resources related to the carbon footprint of different types of food consumption here.  

If you are interested in the topic of sustainable diets you may be interested on FCRN own materials on this issue. For our discussion paper: What is a sustainable healthy diet? See here. For our report Changing what we eat: a call for research & action on widespread adoption of sustainable healthy eating see here. And for our discussion paper Changing consumption: how can we change the way we eat? see here.