This study sought to analyze the effect of work-to-family conflict (demands from work that affect one's family/personal life), family-to-work conflict (demands from family/personal life that affect work), and lack of time for self-care and leisure due to professional and domestic demands on the incidence of weight gain and increase in waist circumference by gender in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). Our study included 9,159 ELSA-Brasil participants (4,413 men and 4,746 women) who attended baseline (2008-2010) and the first follow-up visit (2012-2014). Weight gain and increase in waist circumference were defined as an annual increase ≥ 75th percentile, i.e., ≥ 1.21kg/year and ≥ 1.75cm/year, respectively for women; and ≥ 0.96kg/year and ≥ 1.41cm/year respectively for men. Associations were estimated by Poisson regression applying robust variance with the R software. Analyses were stratified by gender and adjusted for socioeconomic variables. Adjusted models showed a higher risk of weight gain among women who reported family-to-work conflict frequently and sometimes (relative risk - RR = 1.37 and RR = 1.15, respectively) and among those who reported frequent lack of time for self-care and leisure (RR = 1.13). Among men, time-based work-to-family conflict (RR = 1.17) and strain-based work-to-family conflict (RR = 1.24) were associated with weight gain. No associations were observed between work-family conflict domains and increase in waist circumference. These findings suggest that occupational and social health promotion programs are essential to help workers balance work and family life to reduce weight gain.