title: Mechanisms permitting nephrotic patients to achieve nitrogen equilibrium with a protein-restricted diet.
abstract: Clinical experience suggests nephrotic patients are at risk for malnutrition. 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 subjects 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 (BN) was determined and whole body protein turnover measured during fasting and feeding using intravenous -[1-13C]leucine and intragastric -[5,5, 5- 2H3]leucine. BN was positive in both nephrotic and control subjects consuming either diet and rates of whole-body protein synthesis, protein degradation, and leucine oxidation did not differ between groups. In both nephrotic and control subjects anabolism was due to a suppression of whole-body protein degradation and stimulation of protein synthesis during feeding. The principal compensatory response to dietary protein restriction was a decrease in amino acid oxidation and this response was the same in both groups. With the low protein diet leucine oxidation rates during feeding correlated 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 BN in nephrotic patients; (b) nephrotic patients activate normal anabolic responses to dietary protein restriction (suppression of amino acid oxidation) and feeding (stimulation 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.
authors.affiliation: Department of Medicine and George M. O'Brien Research Center for Diseases of the Kidney, Rollins School of Public Health, Emory University, Atlanta, Georgia 30322, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Maroni
authors.forename: C
authors.initials: C
authors.lastname: Staffeld
authors.forename: V R
authors.initials: VR
authors.lastname: Young
authors.forename: A
authors.initials: A
authors.lastname: Manatunga
authors.forename: K
authors.initials: K
authors.lastname: Tom
mesh_terms: D000328:Adult; D000368:Aged; D002247:Carbon Isotopes; D003903:Deuterium; D018753:Diet, Protein-Restricted; D005260:Female; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D008954:Models, Biological; D009404:Nephrotic Syndrome / Q000178:diet therapy* / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D011507:Proteinuria; D012016:Reference Values
chemical_list: D002247:Carbon Isotopes; D003903:Deuterium; D007930:Leucine; D009584:Nitrogen