(A)symmetries in beauty-status exchange: Spousal relative income and partners' BMI (at) during marriage

Beauty-status exchange, while extensively researched as a static concept at match formation, received very little to no attention as a dynamic phenomenon that can occur during marriage. Prior research typically relied on absolute income measures, whereas relative ones are theoretically better at capturing exchange. This study addresses these gaps by examining the existence, extent and nature of the dynamic "beauty-status exchange" as compared to the static one. Using PSID data (1999-2019; 3744 couples) this is the first study to analyse changes in physical attractiveness (approximated by BMI) in response to relative income shifts. The results reveal asymmetrical, gendered exchange patterns at marriage selection, however, during marriage, the effects are symmetrical: increase in one spouse's relative income is associated with a lower BMI in the other, as well as a reduced log odds of being overweight or obese. This income shift is linked to greater physical activity in the other spouse, suggesting purposeful behavioural adjustments. Finally, heterogeneity analyses show the beauty - status exchange is concentrated among highly educated women: the positive association between women's BMI and obesity likelihood, and her relative income is significantly steeper for college educated women. Conversely, the negative association between wives' relative income and husbands' log-odds of obesity is attenuated or reversed among college-educated men, suggesting that in dual-career, high-skill men, rising spousal income may increase work incentives and shift investments away from appearance.