Trends in overweight and obesity in relation to weight change attempts in young adulthood: cross-sectional and repeated measurements from a population-based health study, the Fit Futures study

Abstract Background : Young adulthood is a key period for the development of overweight and obesity; however, less is known about changes in BMI and weight-related behaviors across this life stage. The aim of this study was therefore to examine sex-specific patterns of body mass index (BMI), overweight, obesity, and weight-change attempts at ages 18 and 27 years, and whether weight-change attempts at age 18 were associated with subsequent BMI change. Methods : We used data from the Fit Futures study, a population-based cohort study conducted in Northern Norway. Cross-sectional analyses included 775 participants aged 17–20 years at Fit Futures 2 (2012–2013) and 654 participants aged 26–29 years at Fit Futures 3 (2021–2022). Repeated measurement analyses included 524 participants with valid BMI measurements at both time points. Height and weight were measured using standardized procedures. Weight-change attempts were self-reported. Analyses were stratified by sex, and linear regression was used to examine whether weight-change attempts at age 18 were associated with subsequent BMI change. Results : In repeated measurement analyses, mean BMI increased significantly between ages 18 and 27 in both females and males, from 23.12 to 25.55 kg/m² and from 23.40 to 26.00 kg/m², respectively. The combined prevalence of overweight and obesity approximately doubled in both sexes between ages 18 and 27. The prevalence of obesity alone increased from 7.5% to 19.3% and from 8.1% to 16.7% in females and males, respectively. Among participants with overweight at age 18, 52% of females and 30% of males had progressed to obesity by age 27. Weight-loss attempts were common among females at both ages and increased markedly among males, from 24.8% at age 18 to 38.5% at age 27. Weight-change attempts at age 18 were not significantly associated with subsequent BMI change in either sex. Conclusions : Although weight-loss attempts were common and persistent, BMI and the prevalence of overweight and obesity increased substantially from late adolescence to young adulthood, with a particularly marked increase in obesity. These findings support the need for population-level obesity prevention strategies that extend beyond individual behavior change.