Abstract Background Increased rates of overweight/obesity have been reported in recent years in developed countries. This population study of healthy subjects evaluated the changes in overweight/obesity prevalence in 2003, compared with 1993, and determined the association of age, sex and leisure-time activity with body mass index (BMI), fat-free mass index (FFMI) and fat mass index (FMI). Design Two transversal samples of convenience. Participants Healthy volunteers (1993, n=802; 2003, n=1631). Methods Fat-free mass was determined using the bioelectrical impedance multiple regression equation. Multivariable linear regression, including confounding variables (age, sex, leisure-time activity), was used to model the body composition evolution between the 1993 and the 2003 subjects. Results BMI and FMI were higher in 2003 than in 1993, P<0.001. FFMI was not higher in 2003 than in 1993, P=0.38. More subjects were overweight/obese in 2003 than in 1993 (27.5 versus 17.2%, chi-square P<0.001), and had a high FFMI (30.2 versus 21.8%, chi-square P<0.001) and high FMI (28.0 versus 20.3%, chi-square P<0.001). Multivariate linear regressions showed that leisure-time activity was negatively, and sex, age and inclusion year were positively associated with BMI, FFMI and FMI (the exception was a negative association with sex) (P<0.001). Conclusion Overweight prevalence increased between 1993 and 2003 in a Swiss city, and was associated with a higher fat mass. This observation remained statistically significant after adjustment for age, sex and leisure-time activit
