Role of Low Protein and Low Phosphorus Diet in the Progression of Chronic Kidney Disease in Uremic Rats

Restriction of dietary protein is useful for chronic kidney disease (CKD) patients to protect residual renal function. However, the mechanism by which a low protein diet confers a beneficial effect in CKD patients remains unknown. One possibility is that the benefit from a low protein diet is associated with phosphorus restriction. The aim of this study is to compare the effect of protein and phosphorus on the progression of renal insufficiency using irreversible Thyl rats, which histopathologically resemble IgA nephropathy. Irreversible Thyl rats were fed six types of isocaloric diets consisting of three levels of protein (16.9, 12.6, and 8.4%) and two levels of phosphorus (0.5 and 0.3%) for 13 wk. Renal function was assessed biochemically and histopathologically. The low phosphorus (0.3%) diets showed protection of residual renal function regardless of dietary protein content in uremic rats. With the normal phosphorus (0.5%) diets, however, only the very low protein (8.4%) diet showed a beneficial effect, indicating that dietary phosphorus is a more important factor that affects the progression of renal insufficiency than dietary protein in this model. Furthermore, the low phosphorus diet also prevented an increase in serum parathyroid hormone, indicating that a low phosphorus diet might have beneficial effects not only for residual renal function but also for renal osteodystrophy, a typical complication of patients with CKD.