Chronic arginine aspartate supplementation in runners reduces total plasmaamino acid level at rest and during a marathon run

Background: Athletes consume arginine and/or aspartate as potential nutriti onal ergogenics. Their metabolic effects are controversial and there is som e evidence that ingestion of large doses of single amino acids can adversel y affect the nitrogen balance or induce an amino acid imbalance. Neverthele ss, the general metabolic influence of an arginine aspartate supplementatio n during a prolonged exercise bout has not yet been investigated. Aim of the study: The aim of this study was, therefore, to investigate the general metabolic impact of a chronic supplementation with arginine asparta te in endurance-trained athletes at rest and during a marathon run. Methods: Fourteen endurance-trained runners participated in this field stud y which was carried out according to a double-blind crossover design. 15 g of arginine aspartate or a carbohydrate-based placebo were supplemented dai ly for 13 days before a marathon run. Blood samples for analysis of metabol ites and hormones were collected shortly before the run, after 31 km, at th e end of the run. and after a recovery period of two hours. Additionally, t he respiratory exchange ratio was determined during the run. Results: The plasma level of carbohydrate (glucose, lactate, pyruvate) and fat metabolites (fatty acids, glycerol, beta-hydroxybutyrate), cortisol, in sulin, ammonia, lactate dehydrogenase, and creatine kinase as well as the r espiratory exchange ratio were unaffected by the supplementation. In contra st, the plasma level of somatotropic hormone, glucagon, urea, and arginine were significantly increased, and the level of most of the remaining plasma amino acids as well as their sum was significantly reduced. Conclusions: There was no obvious metabolic benefit derived from the chroni c supplementation with arginine aspartate. And since furthermore the conseq uences of a reduction of the total plasma amino acid level are not known, t he practice of using single amino acid supplements as potential ergogenics should be critically reevaluated.