Background:The prevalence of excess bodyweight, commonly measured as body mass index (BMI)5 kg/m(2), has increased substantially in many populations worldwide over the past three decades, but the rate of increase has slowed down in some western populations.Objectives:We address the hypothesis that the slowing down of BMI trend increases in England reflects a majority sub-population resistant to further BMI elevation.Design:Pseudo panel data derived from annual cross-sectional surveys, the Health Surveys for England (1992-2010). Trends in median BMI values were explored using regression models with splines, and gender-specific mixture model (latent class analysis) were fit to take account of increasing BMI distribution variance with time and identify hidden subgroups within the population.Subjects:BMI was available for 164 155 adults (men; 76 382: women; 87 773).Results:To 2001, the age-adjusted yearly increases in median BMI were 0.140 kg/m(2) and 0.139 kg/m(2), for men and women, respectively, decreasing thereafter to 0.073 kg/m(2) and 0.055 kg/m(2) (differences between time periods, both P values <0.0001). The mixture model identified two components - a normal BMI and a high BMI sub-population - the proportions for the latter were 23.5% in men; 33.7% in women. The remaining normal BMI populations were 'resistant' with minimal increases in mean BMI values over time. By age, mean BMI values in the normal BMI subpopulation increased greatest between 20 and 34 years for men; for women, the increases were similar throughout age groups (slope differences, P<0.0001).Conclusions:In England, recent slowing down of adult BMI trend increases can be explained by two subpopulations-a high BMI subpopulation getting 'fatter'; and a majority 'resistant' normal BMI subpopulation. These findings support a targeted, rather than a population-wide, policy to tackle the determinants of obesity.International Journal of Obesity accepted article preview online, 2 September 2013. doi:10.1038/ijo.2013.161.