Nutritional Inequality and Its Socioeconomic and Environmental Determinants

Abstract

This dissertation consists of three essays that explore dietary inequality, methodological advances in measuring nutrition-related disparities, and the nutritional consequences of climate change. Collectively, these studies examine how socioeconomic and environmental forces shape dietary outcomes in China, the United States, and globally. The first essay investigates income-related inequality in diet quality in China during a period of rapid economic growth, using data from the China Health and Nutrition Survey (1997–2011). Results show that average diet quality, as measured by the Chinese Healthy Eating Index (CHEI), improved significantly over the 14-year period. However, dietary improvements initially favored affluent groups, widening inequality before later becoming more equitable. Urban–rural disparities emerged as a primary driver of inequality, alongside differences in health insurance coverage and gender. Oaxaca decomposition reveals that changes in inequality were driven more by behavioral responses to income than by income changes themselves. These findings highlight the need to address non-dietary structural factors, such as health insurance and rural development, in efforts to improve nutritional equity. The second essay introduces a machine learning-based Concentration Index (ML-CI) to more accurately estimate dietary inequality when income is measured categorically, as is common in survey data. Building on the Extended Kakwani-Wagstaff-Doorenbos (KWD) method, simulation results show that ML-CI offers superior precision and robustness in capturing true inequality levels. Applying this method to household-level dietary data from the USDA’s Purchase to Plate Crosswalk (PPC) reveals a clear pro-rich gradient in Healthy Eating Index (HEI) scores in the U.S., with healthier diets concentrated among wealthier households. In contrast, daily per-capita kilocalorie intake exhibits a pro-poor pattern, indicating that while lower-income groups consume more calories, their diets tend to be less nutritious. The final essay presents the first global empirical assessment of how rising temperatures affect actual human nutrient intake. Combining climate records with nationally representative nutrition data from 185 countries (1990–2018), we find that increases in maximum temperature significantly reduce intake of multiple nutrients, including protein, fiber, vitamin A, and seafood omega-3 fats. These effects are highly unequal, with rural children and populations in low-income tropical regions disproportionately affected. Under the high-emission SSP5–8.5 scenario, nutrient intake declines are projected to worsen substantially by 2100, with per-capita seafood omega-3 intake falling over 30% and fiber and vitamin A by more than 25% in some regions. These findings reveal a critical but underexplored dimension of climate vulnerability—declining nutrients, highlighting the urgency of integrating nutrition-sensitive approaches into global climate adaptation and food policy.