Amino acid removal during hemodialysis can be compensated for by protein ingestion and is not compromised by intradialytic exercise: a randomized controlled crossover trial

Background Patients with end-stage renal disease (ESRD) undergoing hemodialysis experience a rapid decline in skeletal muscle mass and strength. Hemodialysis removes amino acids (AAs) from the circulation, thereby lowering plasma AA concentrations and stimulating proteolysis. Objectives In the present study, we evaluate the impact of intradialytic protein ingestion at rest and following exercise on AA removal and plasma AA availability in patients with ESRD. Methods Ten patients (age: 65 +/- 16 y, male/female: 8/2, BMI: 24.2 +/- 4.8 kg/m(2), serum albumin: 3.4 +/- 0.3 g/dL) with ESRD undergoing hemodialysis participated in this randomized controlled crossover trial. During 4 hemodialysis sessions, patients were assigned to ingest 40 g protein or a placebo 60 min after initiation, both at rest (PRO and PLA, respectively) and following exercise (PRO + EX and PLA + EX, respectively). Spent dialysate and blood samples were collected every 30 min throughout hemodialysis to assess AA removal and plasma AA availability. Results Plasma AA concentrations declined by 26.1 +/- 4.5% within 30 min after hemodialysis initiation during all interventions (P < 0.001, eta(2)(p) > 0.79). Protein ingestion, but not intradialytic exercise, increased AA removal throughout hemodialysis (9.8 +/- 2.0, 10.2 +/- 1.6, 16.7 +/- 2.2, and 17.3 +/- 2.3 g during PLA, PLA + EX, PRO, and PRO + EX interventions, respectively; protein effect P < 0.001, eta(2)(p) = 0.97; exercise effect P = 0.32, eta(2)(p) = 0.11). Protein ingestion increased plasma AA concentrations until the end of hemodialysis, whereas placebo ingestion resulted in decreased plasma AA concentrations (time effect P < 0.001, eta(2)(p) > 0.84). Plasma AA availability (incremental AUC) was greater during PRO and PRO + EX interventions (49 +/- 87 and 70 +/- 34 mmol/L/240 min, respectively) compared with PLA and PLA + EX interventions (-227 +/- 54 and -208 +/- 68 mmol/L/240 min, respectively; protein effect P < 0.001, eta(2)(p) = 0.98; exercise effect P = 0.21, eta(2)(p) = 0.16). Conclusions Protein ingestion during hemodialysis compensates for AA removal and increases plasma AA availability both at rest and during recovery from intradialytic exercise. Intradialytic exercise does not compromise AA removal or reduce plasma AA availability during hemodialysis in a postabsorptive or postprandial state.