A growing body of research supports the "economic insecurity" theory of obesity, which posits that uncertainty with respect to one's material well- being may be an important root cause of the modern obesity epidemic. This literature has been limited in the past by a lack of reliable measures of economic insecurity. In this paper we use the newly developed Economic Security Index to explain changes in U.S. adult obesity rates as measured by the National Health and Nutrition Examination Surveys (NHANES) from 1988-2010, a period capturing much of the recent rapid rise in obesity. We find a robust positive and statistically significant relationship between obesity and economic insecurity that holds for nearly every age, gender, and race/ethnicity group in our data, both in cross-section and over time.