The objective of this randomised trial was to determine whether a lifestyle intervention resulting in weight loss and better fitness would be associated with slower loss of mobility in overweight and obese patients with T2D. Additionally, the investigators determined whether differences in the loss of mobility were mediated by weight loss or improved fitness. From 2001 to 2004, obese patients aged 45–74 years with T2D were randomly assigned to an intensive lifestyle-intervention programme or a diabetes support-and-education programme. The lifestyle programme consisted of diet/behaviour modification and increased physical activity. The primary outcome was self-reported limitation in mobility, with annual assessments for 4 years and 5016 participants contributed to the data