Relationship between marital status and body mass index in Japan

This study examined the relationship between marital status and body mass index (BMI) using data collected from the Japan Household Panel Survey from the period 2009–2018. The varying effects of marital status and changes in such status across the BMI distribution were explored using fixed effects ordinary least square and unconditional quantile regression with fixed effects. Based on the analysis, three key points were identified. First, although marital status does not significantly affect BMI for men, BMI tends to be higher among married women than unmarried women. Second, a positive and significant relationship between marriage and BMI was observed among women under the age of 40, and the effect was largest at the 90% percentile of the BMI distribution. Third, the transition from single to married status has positive yet short-lived effects on BMI for men. Contrastingly, the effects are persistent for women, and the effect is largest at the top of the BMI distribution. The results confirm previous findings that marriage confers weight gain even in Japan, where rates of obesity are significantly lower than in other developed countries.