The aim of this study therefore, is to assess determinants of insulin-induced weight gain in type 2 diabetes mellitus. In a retrospective and cross-sectional study (Jansen HJ et al., submitted) two extreme subgroups were identified (subjects with a weight gain above 80th percentile) and subgroup non-weight gainers (subjects with a weight gain below the 20th percentile). It was found that the gainers had less energy expenditure after initiation of insulin therapy than non-weight gainers. Therefore, the primary aim of this study is to detect an association between energy expenditure and weight gain