Despite the plausible impact of working long hours on obesity, a legal workweek has not received much attention as a policy tool for tackling obesity. Relevant scholarly evidence is also meager. Beginning in 2004, the Korean government lowered the legal workweek from 44 to 40 hours. Using the longitudinal data from the 2005, 2007, and 2008 waves of the Korea Labor and Income Panel Study (N = 1,383 persons or 3,977 person-years), we examine how this four-hour reduction affected male workers’ body mass index (BMI) with ordinary least squares regressions and their obesity with logit regressions. Results show the reduction to the 40-hour workweek lowered both BMI (β = -0.220, p < 0.10) and obesity (β = -0.242, p < 0.05). Our research implies that working long hours causes obesity. Government regulation of the maximum work hours would be effective occupational interventions for overcoming obesity.

□ Key Words: Legal workweek, Long work hours, Obesity, BMI