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The effects of a low-protein diet on the serum insulin-like growth factor (IGF)-1 and IGF binding proteins (IGFBP) were investigated during a 3-month controlled study in 12 adult chronic renal failure patients. Six patients were randomly supplemented with keto acids (Cetolog, Clintec, Velizy, France). Protein intake was prescribed so that both groups were isonitrogenous. Dietary survey included a monthly 3-day food record and a 24-h urinary urea measurement. After a 4- to 6-wk equilibrium period (1.11 g of protein, 32 kcal/kg body wt per day), patients reduced their protein intake to 0.71 g protein/kg body wt per day. Energy intake was kept constant (31 kcal/kg body wt per day) during the 3-month period. Serum IGF-1 levels were in normal range and, for 11 of the 12 patients, were correlated with the GFR (P = 0.01). These serum IGF-1 values did not decrease after reducing the protein intake. By Western ligand blotting, serum IGFBP1, IGFBP2, and IGFBP4 levels were significantly higher than normal adults, whereas the IGFBP3 level was not increased. IGFBP were not modified when protein intake was reduced. The IGFBP1 level was elevated despite a normal insulin level. IGFBP4 changes were inversely correlated with IGF-1 variations. There was no difference between groups receiving or not receiving the keto acids. Thus, in adult chronic renal failure, reducing protein intake by 40% did not modify the growth hormone/IGF-1/IGFBP axis.