How is lean body mass conserved with the very-low protein diet regimen?

Eight CRF patients (GFR = 18.8 +/- 2.7 ml/min) underwent a crossover comparison of a very-low-protein diet (VLPD) providing 0.28 g protein and 35 kcal/kg/day, plus an isomolar mixture of ketoacids (KA) or essential amino acids (EAA). During each dietary period, a 5-day nitrogen balance (BN) was performed and whole-body protein turnover (WBPT) was measured during fasting and feeding using intravenous [1-13C]leucine and intragastric [5,5,5-2H3]leucine. Although the VLPD/KA regimen contained 15% less nitrogen, BN was neutral and did not differ between the regimens. Similarly, rates of WBPT did not differ between the KA or EAA regimens, and neutral BN was achieved by a marked suppression of amino acid oxidation and postprandial inhibition of protein degradation (PD). Participants were then discharged on the VLPD/KA regimen and monitored as outpatients for > or = 1 year. Repeat BN was neutral and rates of WBPT did not differ from baseline values. Thus, the adaptive responses to dietary protein restriction are sustained during long-term therapy.