• Recently, a renewed interest in the role of dietary protein intake in the treatment of progressive renal disease has occurred. Early investigators suggested that high protein intake had a deleterious effect on renal function. Animals fed a high protein intake had more proteinuria and more-extensive glomerular sclerosis compared with animals fed a normal protein intake. More recent investigations have revealed that not only will a high protein intake exacerbate renal disease but a low protein intake will slow and/or prevent decline in renal function and the severity of renal histologic changes. These studies have provided the stimulus for investigations involving humans. Such studies suggest that patients with progressive renal disease of various causes, when placed on low-protein diets (0.6 g/kg/d), exhibit a slowing of the decline in renal function. The mechanism of the halting of such progression has been suggested to be a reduction in the hyperfiltration that occurs in the remaining nephrons after renal injury is established. Micropuncture studies have indicated that after the kidney has suffered injury, either through disease process or surgical removal, the unaffected nephrons try to maintain overall function, with individual nephrons increasing their filtration. This increase in single-nephron glomerular filtration rate (GFR) is accompanied by increases in single-nephron blood flow and an increase in transcapillary pressure, with altered membrane permeability, resulting in increased proteinuria. This increase in filtered albumin is taken up by the mesangium, with resulting mesangial expansion and glomerular sclerosis, with impingement on the glomerular filtering surface area, ultimately resulting in further decreases in GFR. Lowering protein intake will prevent this hyperfiltration, albuminuria, and the histologic changes. Furthermore, whether reduced protein intake is needed during times of physiologic increases in GFR (pregnancy, unilateral nephrectomy) is not clear. The processes that occur from the time after ingestion of protein to changes in GFR are not known but are probably mediated by systemic or intrarenal hormones. When adjusting protein intake, the minimum recommended dietary allowance for daily protein requirements must be considered. In adults, this level is 0.5 g/kg/d, with lower intakes requiring supplementation with essential amino acids. Requirements for children vary according to age—the younger the child, the higher the requirement. Minimum requirements for children with renal insufficiency have not been established. However, reduced protein intake is warranted, in addition to other therapies, in patients with renal insufficiency to reduce the potential for progression to end-stage renal disease.