Protein- and carbohydrate-induced augmentation of whole body creatine retention in humans

G. R. Steenge, E. J. Simpson, P. L. Greenhaff
2000 Journal of applied physiology  
Steenge, G. R., E. J. Simpson, and P. L. Greenhaff. Protein-and carbohydrate-induced augmentation of whole body creatine retention in humans. J Appl Physiol 89: [1165][1166][1167][1168][1169][1170][1171] 2000.-This study investigated the effect of creatine supplementation in conjunction with protein and/or carbohydrate (CHO) ingestion on plasma creatine and serum insulin concentrations and whole body creatine retention. Twelve men consumed 4 ϫ 5 g of creatine on four occasions in combination
more » ... h 1) 5 g of CHO, 2) 50 g of protein and 47 g of CHO, 3) 96 g of CHO, or 4) 50 g of CHO. The increase in serum insulin was no different when the protein-CHO and high-CHO treatments were compared, but both were greater than the response recorded for the low-CHO treatment (both P Ͻ 0.05). As a consequence, body creatine retention was augmented by ϳ25% for protein-CHO and high-CHO treatments compared with placebo treatment. The areas under creatine-and insulin-time curves were related during the first oral challenge (r ϭ Ϫ0.920, P Ͻ 0.05) but not after the fourth (r ϭ Ϫ0.342). It is concluded, first, that the ingestion of creatine in conjunction with ϳ50 g of protein and CHO is as effective at potentiating insulin release and creatine retention as ingesting creatine in combination with almost 100 g of CHO. Second, the stimulatory effect of insulin on creatine disposal was diminished within the initial 24 h of supplementation. insulin; muscle metabolism; diet; exercise MOST OF THE BODY CREATINE pool is restricted to skeletal muscle, where it plays a pivotal role in maintaining energy homeostasis (for extensive reviews, see Refs. 28, 29) . The muscle total creatine store (phosphocreatine and free creatine) in healthy, nonvegetarian subjects is, on average, 124 mmol/kg dry mass (dm), but it can vary widely among individuals (100-150 mmol/kg dm; Refs. 10, 11). Dietary creatine supplementation at a rate of 20 g/day for 5 days has been shown to increase muscle total creatine content by 20% on average (11). A similar, but more gradual, increase can be obtained when creatine is ingested at a rate of 2 g/day for 28 days (13). It has been widely reported that elevating the muscle total creatine store can enhance performance during high-intensity exercise (1, 2, 8, 21, 26, 27) . As a result of these publications, creatine supplementation has become popular among athletes wishing to improve athletic performance. It is also possible that creatine supplementation may be of therapeutic benefit for patients with muscular and neurological disorders (14, 20, 22, 25) . It has become apparent that the metabolic and physiological effects of creatine supplementation are positively related to the extent of muscle creatine accumulation during supplementation. Specifically, we have suggested that, to exert an optimal effect on performance and metabolism, it would be desirable to increase the muscle total creatine content by at least 20 mmol/kg dm (2, 7). As already stated, creatine supplementation at a rate of 20 g/day for 5 days can increase the muscle total creatine content by 20% on average (20 mmol/kg dm). However, it is important to note that the variation among individuals is large (0-40 mmol/kg dm; Refs. 5, 8, 11) . This variation in creatine accumulation during supplementation can be partly accounted for by differences in presupplementation muscle creatine concentrations and possibly in muscle fiber-type distribution, but it remains unclear why muscle creatine accumulation can be different by up to sixfold among individuals with similar presupplementation creatine concentrations (2). Our laboratory has previously reported that creatine ingested in combination with simple carbohydrates (CHO) substantially increased muscle creatine accumulation compared with the ingestion of creatine alone (5). Furthermore, ingestion of creatine in conjunction with CHO reduced the interindividual variability in the magnitude of muscle creatine accumulation, such that all subjects demonstrated an increase in muscle total creatine content Ն20 mmol/kg dm. In agreement with animal-based research, it was proposed that the stimulatory effect of CHO on muscle creatine accumulation was due to insulin-enhancing muscle creatine uptake, probably by stimulating sodium-potassium pump activity (12, 19) . Recently, our laboratory has confirmed that insulin can increase creatine accumulation in human skeletal muscle but only when present at a concentration close to, or in excess of, 100 mU/l (24). On the basis of these findings, it is clear that creatine supplements would need to be ingested with
doi:10.1152/jappl.2000.89.3.1165 pmid:10956365 fatcat:u7tohqclubg3zdan4lrcn5g6ru