Climate/Environment, Health and Improved Nutrition
Objectives : The climate impacts of human food systems have been well documented. Guidance to individuals to reduce their dietary carbon footprint would benefit from simple advice, but little is known about the impact of simple changes on self-selected diets. Here we examine a random sample of high-impact diets from the U.S. to test the effects of a single change in each diet on greenhouse gas emissions (GHGE) and nutritional quality.
Methods : Based on an extensive review of lifecycle assessment studies in the environmental sciences literature, we created a database of Food Impacts on the Environment for Linking to Diets (dataFIELD). We matched impact data from dataFIELD to the 24-hour recall dietary data in the 2005-2010 waves of the National Health and Nutrition Examination Survey (NHANES). For all adults with reliable diets (N=16,800), we calculated their dietary carbon dioxide equivalents per 1000 kcal (kg CO2-eq 1000 kcal-1), a density measure of GHGE. A 10% random sample (N=330) of all diets in the top quintile of this variable was selected. The single food item with the highest GHGE was identified in each of these high-impact diets and was substituted for an equal-calorie amount of a similar, but lower impact food (e.g. chicken for beef). Each of the 330 diets were then re-evaluated on total GHGE/1000 kcal and on the Healthy Eating Index, a summary measure of nutritional quality developed for the U.S. population.
Results : The food with the highest impact in each of the randomly chosen diets was most often a type of beef (52%), a mixed dish with beef (33%), or a shellfish/shellfish mixed dish (10%). After single-item substitutions were made for these foods with equivalent poultry-based items, the mean impact from this sample of diets dropped (p < .001) from 4.35 ± 0.1 to 1.95 ± 0.8 kg CO2-eq 1000 kcal-1. This represents a 54% reduction in average dietary greenhouse gas emissions from diets. Healthy Eating Index values for the revised diets showed slight improvements.
Conclusions : Simple substitutions can be made in individuals' diets to reduce their carbon footprints, without sacrificing dietary quality. If promoted on a wide-scale basis, such a strategy could substantially reduce greenhouse gas emissions from the U.S. diet.
Funding Sources : Wellcome Trust.