Skeletal muscle and nutritional assessment in chronic renal failure patients on a protein-restricted diet

Background. The close relationship between protein-energy malnutrition and quality of life, morbidity and mortality, makes mandatory a careful evaluation of the nutritional status and muscle mass in chronic renal failure (CRF) patients. Methods. Nutritional and skeletal muscle data were obtained from 28 nondiabetic patients with severe CRF (glomerular filtration rate, GFR < 15 mL min(-1)) on conservative treatment. Of them, 14 (8 males, 4 females) were on a conventional low-protein (0.6 g kg(-1) body weight) diet (LPD) and 14 (8 males, 4 females) were on a very low-protein (0.3 g kg(-1) body weight) diet supplemented with essential amino acids and ketoacids (Ketodiet); 28 healthy sex- and age-matched subjects served as controls. We evaluated biochemistry, anthropometry, bioelectrical impedance vector analysis, and three noninvasive tests investigating some skeletal muscle features: (a) myoelectrical fatigue phenomenon was studied using a surface electromyography technique that provides data on conduction velocity (CV), median frequency of power spectrum (MDF) and average rectified value (ARV) of myofibre action potential, at 15 and 35 Hz stimulation frequency; (b) muscle oxidative metabolism was studied by serum lactate following aerobic exercise; and (c) muscle strength of the legs was studied using an isokinetic exercise test at two different angular velocities (60degrees and 180degrees s(-1)). Results. No difference between patients and controls was detected regarding CV, MDF and ARV, at 35 and 15 Hz testing. Serum lactate was higher in patients than in controls at 1, 5, 10 and 30 min recovery. A decreased knee extension and flexion strength was detected in CRF patients both at low (60degrees s(-1)) and at high (180degrees s(-1)) angular velocity; muscle strength deficit negatively correlated to serum albumin (r = -0.52, P < 0.01), but no relationship was found with protein intake or residual renal function. No difference was found between LPD and Ketodiet patients regarding the studied muscular tests as well as the anthropometry and bio-impedance data. Conclusions. Implementation of a proper dietary regimen, including severe restriction of protein intake can preserve lean body mass and nutritional status of advanced CRF patients. Skeletal muscle shows unchanged sarcolemma excitability but abnormal oxidative metabolism and reduced segmental strength. Regular physical activity and a close clinical and dietary monitoring should be recommended for the predialysis patient care.