Food choices in the United States
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Description
Evidence indicates that changing from current Western-style dietary patterns can improve health as well as reduce environmental impact from agricultural greenhouse gas emissions (GHGE). However, most studies look only at a single aggregate datapoint, and very few have been conducted on US diets. This dissertation addresses these gaps by using individual self-selected dietary data from adults ages 18+ in the nationally representative National Health and Nutrition Examination Survey (NHANES). Paper 1 identified consumers who might be willing to change their dietary behaviors for sustainability reasons and calculated changes to diet quality, carbon footprint, and cost if these individuals were to replace beef with other protein foods. Replacing beef with poultry reduced food-related GHGE 35.7%, increased Healthy Eating Index (HEI) score by 1.7%, and reduced diet cost by 1.7%. Paper 2 developed new commodity recipes to be able to calculate food-related GHGE over a 10-year period. US food-related carbon footprints did not change significantly between 2005-2006 and 2015-2016 (-0.14 kg CO2-equivalents/2000kcal, p=0.18). However, there were significant differences by socioeconomic and demographic factors. Women had lower food-related emissions than men (-0.38 kg CO2-equivalents/2000kcal, p<.001), and the Silent Generation, Millennials, and Generation Z had lower food-related emissions than Baby Boomers. These generational differences likely stem from beef consumption significantly declining in all generations except Boomers. Paper 3 used multivariate Markov Chain Monte Carlo (MCMC) modeling to estimate usual or habitual food-related GHGE and HEI scores for the 2015-2016 NHANES. The usual distribution of food-related GHGE has substantially smaller left and right tails than previous work using 1-day dietary data. However, similar to results with 1-day dietary data, there is a significant inverse relationship (p trend = 0.010) between food-related emissions and diet quality, with the mean HEI score of low-GHGE diets being 6.5/100 points higher than high-GHGE diets. Substantial environmental benefits are possible from dietary changes, especially those that reduce beef consumption and replace it with poultry or plant-based protein foods, and diets with these characteristics tend to have higher diet quality. However, US diets are not moving in the desired direction with respect to diet quality or climate impacts. More efforts, such as nutrition education programs, social marketing, and inclusion of sustainability in the Dietary Guidelines for Americans, are needed to achieve health and environment co-benefits.