Effects of a Ketoacid Supplementation on Urinary Urea Nitrogen Excretion in Patients With Stage III to IV Renal Failure

Patients with an estimated glomerular filtration rate of less than 25 ml/kg/min, not on renal substitution therapy, without important concomitant diseases and aged between 40 and 70 years, will be invited to participate in the study. They will be randomly assigned to a group that will receive receive a supplement of ketoacids (Ketosteril) 1 tablet containing 630 mg of ketoacids every 5 kg of body weight and a diet containing 25 to 35 kcal/kg and 0.3 g/protein per day or to a group receiving placebo and a diet containing 25 to 35 kcal/kg and 0.6 g/protein per day. The intervention will last 16 weeks. At baseline and the end of the intervention a blood sample will be obtained to measure creatinine, urea nitrogen and cystatin C. Also a spot urine sample will be obtained to measure urea nitrogen and creatinine excretion. The compliance with the dietary prescription and the ketoacid or placebo supplement will be assessed every 2 weeks.