Patients with type 2 diabetes often have an unhealthy diet and are overweight with little muscle mass. In order to prevent complications of diabetes, it is very important to objectively assess lifestyle factors prior to an intervention. In this thesis, performed within the DIAbetes and Lifestyle Cohort Twente (DIALECT), collection of a 24-hour urine sample was an important tool, in which muscle mass and dietary protein intake can be calculated based on creatinine and urea. In contrast with existing literature, our main finding was that unrestricted dietary protein intake was not associated with an increased hazard of renal function deterioration. Remarkably, about 10% of patients with type 2 diabetes had a dietary protein intake below 0.8 grams per kilogram body weight, despite the fact that dietary protein restrictions have not been indicated in either of the CKD stages. Another important finding was that the 24-hour urinary excretion of creatinine not only reflects muscle mass, but also muscle functional status. Since low muscle mass (sarcopenia) is associated with adverse clinical outcomes, it is useful to consider assessment of 24-hour excretion of creatinine excretion for indirect assessment of sarcopenia. High dietary protein intake appears to be an important factor in preventing sarcopenia. This is of utmost importance in patients with chronic kidney disease, because they have a lower dietary protein intake and a lower muscle mass compared with patients without chronic kidney disease. These findings provide new insights for optimizing lifestyle management in patients with type 2 diabetes.