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of protein intake above that currently recommended. Cur- rently, the RDA for protein in healthy adults is 0.8 g/kg body weight per day [1]. The purpose of this recommen- dation was to account for individual differences in protein metabolism, variations in the biological value of protein, and nitrogen losses in the urine and feces. Many factors need to be considered when determining an optimal amount of dietary protein for exercising individuals. These factors include protein quality, energy intake, car- bohydrate intake, mode and intensity of exercise, and the timing of the protein intake [2]. The current recom- mended level of protein intake (0.8 g/kg/day) is estimated to be sufficient to meet the need of nearly all (97.5%) healthy men and women age 19 years and older. This amount of protein intake may be appropriate for non- exercising individuals, but it is likely not sufficient to off- set the oxidation of protein/amino acids during exercise (approximately 15% of the total energy cost of exercise) nor is it sufficient to provide substrate for lean tissue accretion or for the repair of exercise induced muscle dam- age [3,4]. ance assessment and amino acid tracer studies. The nitro- gen balance technique involves quantifying the total amount of dietary protein that enters the body and the total amount of the nitrogen that is excreted [5]. Nitrogen balance studies may underestimate the amount of protein required for optimal function because these studies do not directly relate to exercise performance. Also, it is pos- sible that protein intake above those levels deemed neces- sary by nitrogen balance studies may improve exercise performance by enhancing energy utilization or stimulat- ing increases in fat-free mass in exercising individuals [2]. Indeed, an abundance of research indicates that those individuals who engage in physical activity/exercise require higher levels of protein intake than 0.8 g/kg body weight per day, regardless of the mode of exercise (i.e. endurance, resistance, etc.) or training state (i.e. recrea- tional, moderately or well-trained) [6-13]. Also, there is a genuine risk in consuming insufficient amounts of pro- tein, especially in the context of exercise; a negative nitro- gen balance will likely be created, leading to increased catabolism and impaired recovery from exercise [14]. intakes range from of 1.0 g/kg to 1.6 g/kg per day [2,4,7,15] depending on the intensity and duration of the endurance exercise, as well as the training status of the individual. For example, an elite endurance athlete requires a greater level of protein intake approaching the higher end the aforementioned range (1.0 to 1.6 g/kg/ day). Additionally, as endurance exercise increases in branched-chain amino acids, which creates a demand within the body for protein intakes at the upper end of this range. Strength/power exercise is thought to increase protein requirements even more than endurance exercise, particularly during the initial stages of training and/or sharp increases in volume. Recommendations for strength/power exercise typically range from 1.6 to 2.0 g/ kg/day [3,11-13,16], although some research suggests that protein requirements may actually decrease during train- ing due to biological adaptations that improve net protein retention [17]. that are intermittent in nature (e.g., soccer, basketball, mixed martial arts, etc.). In a review focusing on soccer players, a protein intake of 1.41.7 g/kg was recom- mended [18]. Protein intakes within this range (1.4 to 1.7 g/kg/day) are recommended for those engaging in other types of intermittent sports. of Sport Nutrition that exercising individuals ingest pro- tein ranging from 1.4 to 2.0 g/kg/day. Individuals engag- ing in endurance exercise should ingest levels at the lower end of this range, individuals engaging in intermittent activities should ingest levels in the middle of this range, and those engaging in strength/power exercise should ingest levels at the upper end of this range. chronically high protein intake is unhealthy and may result in unnecessary metabolic strain on the kidneys leading to impaired renal function. Another concern that is often cited is that high protein diets increase the excre- tion of calcium thereby increasing the risk for osteoporo- sis. Both of these concerns are unfounded as there is no substantive evidence that protein intakes in the ranges suggested above will have adverse effects in healthy, exer- cising individuals. and kidney function is the belief that habitual protein consumption in excess of the RDA promotes chronic renal disease through increased glomerular pressure and hyper- filtration [19,20]. The majority of scientific evidence cited by the authors [20] was generated from animal models and patients with co-existing renal disease. As such, the extension of this relationship to healthy individuals with normal renal function is inappropriate [21]. In a well designed prospective cohort study, it was surmised that high protein intake was not associated with renal func- tional decline in women with normally operating kidneys [22]. Also, it has been reported that there are no statisti- |
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