Contributions of leisure-time physical activity and sedentary behaviour to major weight gain among young and early midlife women and men

To examine the associations of leisure-time physical activity (LTPA) and leisure-time sedentary behaviour (LTSB) with major weight gain among young and early midlife women and men. We used data from the employees of the City of Helsinki aged 19–39 years in 2017 (Phase 1), followed-up in 2022 (Phase 2, n = 2606, 80% women). LTPA and LTSB were categorized into three groups, and a 4-class joint variable was constructed. Major weight gain was defined as a 10% or more increase in body weight from Phase 1 to Phase 2. Logistic regression analysis estimated odds ratios (ORs) with 95% confidence intervals (CIs), adjusting for sociodemographic and health-related factors. One in four women (24.2%) and one in ten men (11.6%) reported major weight gain over the five-year follow-up. Participants engaging in moderate (OR 1.28, 95% CI 1.02–1.60) or low LTPA (OR 1.45, 95% CI 1.08–1.94) were more likely to have gained weight of 10% or more than participants engaging in vigorous LTPA when adjusted for gender, age and BMI in Phase 1. Participants in the joint category of low/moderate LTPA and high LTSB had higher odds of major weight gain than those in either single-exposure category (OR 1.73, 95% CI 1.21–2.52), and this association remained statistically significant after full adjustment. Low/moderate LTPA combined with high LTSB was associated with major weight gain, which highlights the importance of considering the combined effect of physical activity and sedentary behaviour when addressing the risk of weight gain in young and early midlife adults.