We explored the extent to which economic contextual factors moderated the association of Supplemental Nutrition Assistance Program (SNAP) participation with body mass index (BMI) among low-income adults whose family income (adjusted for family size) is less than 130% of the federal poverty guideline. We drew on individual-level data from the Panel Study of Income Dynamics in the United States, including three waves of data in 1999, 2001, and 2003. Economic contextual data were drawn from the American Chamber of Commerce Researchers Association for food prices and Dun & Bradstreet for food outlet measures. In addition to cross-sectional estimation, a longitudinal individual fixed effects model was used to control for permanent unobserved individual heterogeneity. Our study found a statistically significant joint moderating effect of the economic contextual factors in longitudinal individual fixed effects model for both women (BMI only) and men (both BMI and obesity). For both women and men, SNAP participants' BMI was statistically significantly lower if they faced increased numbers of available supermarkets/grocery stores in the longitudinal model. A simulated 20% reduction in the price of fruits and vegetables resulted in a larger decrease in BMI among SNAP participants than non-participants for women and men, whereas a simulated 20% increase in the availability of supermarkets and grocery stores resulted in a statistically significant difference in the change in BMI by SNAP participation for women but not for men. Policies related to economic contextual factors, such as subsidies for fruits and vegetables or those that would improve access to supermarkets and grocery stores may enhance the relationship between SNAP participation and body mass outcomes among food assistance program participants.
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