Social scientists often speculate that both acculturation and socioeconomic status are factors that may explain differences in the body weight between Mexican Americans and whites and between Mexican Americans and Mexican immigrants, yet prior research has not explicitly theorized and tested the pathways that lead both of these upstream factors to contribute to ethnic/ nativity disparities in weight. We make this contribution to the literature by developing a conceptual model drawing from Glass and McAtee’s (2006) risk regulation framework. We test this model by analyzing data from the 1999 2012 National Health and Nutrition Examination Survey (NHANES). Our conceptual model treats acculturation and socioeconomic status as risk regulators, or social factors that place individuals in positions where they are at risk for health risk behaviors that negatively influence health outcomes. We specifically argue that acculturation and low socioeconomic status contribute to less healthy diets, lower physical activity, and chronic stress, which then increases the risk of weight gain. We further contend that pathways from ethnicity/nativity and through acculturation and socioeconomic status likely explain disparities in weight gain between Mexican Americans and whites and between Mexican immigrants and whites. Study results largely support our conceptual model and have implications for thinking about solutions for reducing ethnic/nativity disparities in weight.