Proteinuria has a direct toxic effect on the kidney and is a predictor of renal disease progression and outcome also in nondiabetic patients. Controlling proteinuria by reducing the dietary protein intake slows the progression of renal damage, as has been demonstrated in many experimental and clinical studies with low-protein diets (LPD). Serum albumin increases in LPD-treated kidney patients due to reduced urinary excretion. Moreover, it has been observed that LPD-treated kidney patients can keep an adequate nitrogen balance. Association of LPD with ACE inhibitors or sartans has an antiproteinuric effect stronger than that of LPD or antihypertensives alone, which is due to their different hemodynamic actions in the kidney. ACE inhibitors and sartans can be contraindicated in patients with stage 5 chronic kidney disease, where LPD is the only option for proteinuria control. Conflicting results with soy protein-based diets advise against the use of such diets in patients with nephrotic syndrome.