Dietary phosphorus is thought to be a factor that impairs the residual renal function in patients with chronic renal failure, To determine the effect of dietary phosphorus on the prognosis of chronic renal failure, low-phosphorus milk was prepared from normal cow's milk using boehmite, a synthetic phosphate-ion absorbent. Regular diet, normal cow's milk, and low-phosphorus milk were then given to 5/6-nephrectomized rats and the serum levels of inorganic phosphorus, calcium, creatinine. and blood urine nitrogen in the rats in each group were compared. The serum levels of inorganic phosphorus and calcium were not different among the groups, despite a significant difference in phosphorus intakes. On the other hand, serum levels of creatinine (Cr) and blood urine nitrogen (BUN) in the rats fed low-phosphorus milk were significantly lower (Cr. 0.54 +/- 0.054 mg/dl;, BUN, 29.2 +/- 3.90 mg/dl) than those in the rats fed a regular diet (Cr, 0.64 +/- 0.057 mg/dl, BUN, 37.4 +/- 3.55 mg/dl) or normal milk (Cr, 0.61 +/- 0.040 mg/dl; BUN, 34.5 +/- 3.59 mg/dl). No beneficial effect of protein restriction was observed when residual renal functions in rats fed a regular diet and those fed normal milk were compared. The results Suggest that dietary phosphorus plays a major role in the progression of renal failure. (C) 2002 Elsevier Science (USA). All rights reserved.