Do Environmental Factors Drive Obesity? Evidence from International Graduate Students
Almost two-thirds of adults in the United States are obese or overweight (Catenacci et al. 2009). Prevalence of obesity among the US adult population has increased from 22.9 percent in 1994 to 34.9 percent in 2012 (Flegal et al. 2002; Ogden 2014). Obesity now accounts for 5% to 10% of health care costs in the United States; obese men incur $1,152 more in health care expenditures than do men of normal weight, while obese women incur $3,613 more than do women of normal weight (Cawley and Meyerhoefer 2012). Further, obesity has become the leading cause of premature death in the United States (Jia and Lubetkin 2010). Because of these costs, understanding the drivers of obesity is important.
Prior work has sought to identify causal mechanisms that explain the spread of obesity. These include: changes in diet and lifestyles (Mozaffarian et al. 2011), reduced physical activity (Ladabaum et al. 2014), reduced intake of fruits and vegetables (Popkin et al. 2012), increased intake of fast food (Anderson et al. 2011), and through induction via social and geographical networks (Christakis and Fowler 2007). However, because most individuals have considerable control over where they live, identification of environmental factors on weight gain is difficult (Cohen-Cole and Fletcher 2008).
This research attempts to isolate the effect of environmental factors on individual weight gain by studying a unique group of individuals who have limited mobility: International students. Naïve estimates of the relationship between environmental factors and obesity are often plagued by reverse causation, sample selection, and omitted variable bias. In this study, we survey international students at 48 public universities across the United States. We use this unique data to link the prevalence of obesity in a particular region on the weight gain of students. We argue that our estimates are less likely biased as international students have limited control over the environment to which they are exposed upon arrival in the United States.
By studying international students, we are able to offer novel and credible evidence about the ways in which environment drives obesity. When applying to universities in the United States, international students – particularly those from developing countries – may be less aware of the social and cultural conditions that characterize particular university campuses and therefore may apply to universities without regard to such conditions. They may not be offered admission at the universities of choice. Hence, environmental factors driving obesity are less likely related to students’ choice of university. We ask if two otherwise similar international students arrive in the United States but stay in environments where prevailing obesity rate differ, would their weight gain trajectories diverge?
We find that students living in areas with higher prevalence of obesity show a biologically important and statistically significantly greater increase in weight as compared to those living in areas with lower prevalence of obesity. Evidence suggests that the environmental characteristics of a region have a causal effect on the weight gain of individuals.