MECHANISMS PERMITTING NEPHROTIC PATIENTS TO ACHIEVE NITROGEN EQUILIBRIUM WITH A PROTEIN-RESTRICTED DIET

Clinical experience suggests nephrotic patients are at risk for malnut rition. To determine if nephrotic patients can adapt successfully to a protein-restricted diet, nephrotic (glomerular filtration rate, 52+/- 15 ml/min; urinary protein [Uprot.], 7.2+/-2.2 grams/d) and control su bjects completed a crossover comparison of diets providing 0.8 or 1.6 grams protein (plus 1 gram protein/gram Uprot.) and 35 kcal per kg per day. Nitrogen balance (B-N) was determined and whole body protein tur nover measured during fasting and feeding using intravenous L-[1-C-13] leucine and intragastric L-[5,5,5-H-2(3)]leucine. BN was positive in b oth nephrotic and control subjects consuming either diet and rates of whole-body protein synthesis, protein degradation, and leucine oxidati on did not differ between groups. In both nephrotic and control subjec ts anabolism was due to a suppression of whole-body protein degradatio n and stimulation of protein synthesis during feeding. The principal c ompensatory response to dietary protein restriction was a decrease in amino acid oxidation and this response was the same in both groups. Wi th the low protein diet leucine oxidation rates during feeding. correl ated inversely with Uprot. losses (r = -0.83; P < 0.05). Conclusions: (a) a diet providing 0.8 gram protein (plus 1 gram protein/gram Uprot. ) and 35 kcal per kg per day maintains B, in nephrotic patients; (b) n ephrotic patients activate normal anabolic responses to dietary protei n restriction (suppression of amino acid oxidation) and feeding (stimu lation of protein synthesis and inhibition of protein degradation); (c ) the inverse correlation between leucine oxidation and Uprot. losses suggests that proteinuria is a stimulus to conserve dietary essential amino acids.