Dietary management of phosphorus in CKD patients

Hyperphosphatemia is a common complication in advanced chronic kidney disease (CKD), especially end-stage kidney disease. Since the kidney plays a critical role in the maintenance of phosphorus balance, dietary management of phosphorus is the first-line treatment of hyperphosphatemia. Dietary phosphorus intake shows strongly positive association with dietary protein intake. Thus, low protein diet, which is a common dietary treatment in CKD patients, is useful for treatment of hyperphosphatemia. Phosphorus to protein ratio is also considered in dietary management for CKD patients with hyperphosphatemia. Phosphorus to protein ratio is different in foods. Consumption of foods with high phosphorus to protein ratio is significantly associated with mortality in end-stage CKD patients. Plant foods and animal foods are sometimes attractive issues. In general, animal foods have higher phosphorus availability than plant foods. A crossover intervention study demonstrated that vegetarian diet consumption lowered serum phosphorus levels compared to meat diet in CKD patients. Another important issue is food additives. Phosphorus-containing food additives are widely used in various food processing, thus processed foods have higher bioavailability of phosphorus rather than natural foods. We recently proposed "phosphatemic index" that is a novel index can reflect the phosphorus bioavailability. Phosphatemic index is based on postprandial increase in serum phosphorus level following the ingestion of various foods as similar as glycemic index. Phosphatemic index can evaluate more accurately the effect of phosphorus containing foods on serum phosphorus levels compared with phosphorus to protein ratio, plant/animal food ratio. Dietary phosphorus restriction can also affect metabolism of other nutrients including minerals and vitamins. I will discuss dietary management of phosphorus in CKD patients from metabolic points of view.