PROJECT SUMMARY The Supplemental Nutrition Assistance Program (SNAP) is the largest food security program for lower-income households in the U.S., providing financial benefits for grocery purchases to nearly 42 million people (1 in 8). SNAP benefit amounts increased substantially starting in March 2020, most of which was driven by temporary emergency allotments (i.e., supplemental benefits), to bolster food security in response to the COVID-19 pandemic and to ensure participants could afford a healthy diet. These emergency benefits expired across all states in March 2023, a policy that is estimated to have reduced benefits by an average of $175 per household, a ~33% decline. The sudden end of SNAP emergency allotments represents the largest-ever universal reduction in SNAP benefits and could have a major impact on households’ food purchases and their subsequent health. However, this has not been investigated to date. This study will make a significant contribution by evaluating the impact of the expiration of SNAP emergency allotments on participants’ food purchase quality overall, among historically underserved groups with worse food access and pre-pandemic inequities in nutrition-related chronic disease, and in the context of concurrent economic, social, community, and retail factors. We will use a mixed- methods approach that combines a natural experiment of household purchases with qualitative interviews of SNAP participants and those working in the larger food system. In Aim 1, we will analyze longitudinal, loyalty- linked sales data on >440,000 customers of a large Northeast supermarket chain who made purchases from November 2021-February 2023 (16 months before the end of SNAP emergency allotments). We will use controlled interrupted time series (CITS), a quasi-experimental method, to estimate the effect of the end of SNAP emergency allotments on several indices of food purchase quality from April 2023-March 2024 (12 months after the end of allotments) among SNAP-participating households (intervention) vs. non-participating households (control). In Aim 2, we will enroll a cohort of 2,500 lower-income shoppers who shop at the chain and whose purchases can be identified by loyalty number. We will assess household-level data via online surveys and use CITS to examine associations between the end of SNAP emergency allotments and supermarket food purchase quality by rurality, race/ethnicity, and economic stability. In Aim 3, we will explore individual-level factors (e.g., use of other assistance programs, cooking norms, food preferences) by conducting semi-structured qualitative interviews among 45-75 participants from the cohort in Aim 2 who participate in SNAP and represent rural, Black, and Hispanic demographic segments of the study population. We will explore system-level factors (e.g., food availability, supply chains, pandemic era SNAP policy rollout) via interviews with representatives from SNAP implementing agencies, supermarket retailer...