PROTEIN RESTRICTION IN CHRONIC RENAL-INSU FFICIENCY

Irrespective of the underlying renal disease, the loss of renal functi on progresses continuously over time in most forms of chronic renal di seases. This process involves glomerular hemodynamic and nonhemodynami c factors, which, through glomerular hyperperfusion, hyperfiltration a s well as hypertension and through hypertrophy (enlargement) cause glo merulosclerosis, tubulo-interstitial fibrosis and vascular sclerosis. The improved understanding of the pathophysiology of CRF suggests new therapeutic approaches. Large, representative studies conducted over t he past few years have shown that the progression of chronic renal ins ufficiency can be slowed or even stopped by antihypertensive agents (A CE inhibitors), and dietary protein restriction. Normalizing the serum liquid profile, high diuresis, controlling acidosis, and cessation of smoking may also be effective in this respect. In animal experiments, protein restriction influences the functional and morphological distu rbances of the adaptation process through alteration of growth factors (TGF beta, PDGF) and endocrine systems like glucagon, renin, and othe rs and may have a renoprotective effect. The influence of a low-protei n diet on the progression of chronic renal insufficiency in humans has been investigated in studies relating to diabetic and nondiabetic ren al diseases, through the results being partly conflicting. In all, met aanalyses by Fouque and Pedrini have confirmed the positive effect of protein restriction in chronic renal insufficiency. The Modification o f Diet in Renal Disease (MDRD) Study has shown that protein restrictio n to 0.6 g/kg/day for patients in an advanced stage of renal insuffici ency (creatinine clearance 13-24 ml/min) will slow its progression. In contrast, a further reduction of protein supply combined with a suppl ementation of essential aminoacids and ketoacids did not yield any fav orable results. Taken together, these studies and a consensus conferen ce held in 1994 recommend that patients with a moderate impairment of renal function (GFR 25-55 ml/min) should be restricted to 0/6 g/kg/day . In this case, the nutritional status should be checked by determinin g body weight, serum albumin, and transferrin levels. Energy supply mu st be increased to 30-35 kcal/kg/day, if necessary. Target blood press ure for patients with renal insufficiency and proteinuria > 1 g/day sh ould be 125/75 mmHg (the mean arterial blood pressure being 92 mmHg). ACE inhibitors play a leading role in antihypertensive therapy. Accord ing to Gansevoort, the combination of ACE blocker and protein restrict ion may cause a significantly sharper decline of proteinuria than the 2 individual components alone. Moreover, a protein-restrictive diet al so helps to reduce phosphate and lipid supply, thus obtaining probably additional protective effects on chronic renal failure.