This study aimed to evaluate the anti-proteinuric effect of a very-low-protein diet supplemented with essential amino acids and keto analogs in patients with moderate to advanced chronic kidney disease and proteinuria already treated with both ACE inhibitors and angiotensin-receptor blockers. The study was a prospective randomized controlled cross-over trial comparing a very-low-protein diet (VLpD) and a low-protein diet (LpD). We enrolled 32 consecutive patients between June 2000 and June 2005. They were randomized to receive a VpLD (group A) or an LpD (group B) for 6 months; thereafter, patients of both groups were switched to the other diet (group A to LpD; group B to VpLD) for a further 6 months. Finally, all patients were randomized again within each group to receive either LpD or VLpD and were followed for another year. The VLpD group showed a significant reduction of urinary protein excretion during the diet period, with a nadir at the fourth month of treatment; the amount of urinary protein reduction was about 58%. Serum advanced glycation end products (AGE) significantly decreased in 10 patients (5 of group A, 5 of group B; -18% and -19%, respectively) during VLpD. Univariate analysis showed that proteinuria correlated indirectly with VpLD and directly with AGE. This study demonstrates that in patients with moderate to advanced chronic kidney disease and severe proteinuria, a VLpD reduces both proteinuria and serum AGE, even in the presence of complete inhibition of the renin-angiotensin system.