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individual. humans at rest, protein balance increases by either decreasing the rate of protein breakdown, increasing the rate of protein synthesis or a combination of both [55,56]. Following resistance exercise in males it has been shown that the addition of free leucine combined with carbohy- drate and protein led to a greater increase protein synthe- sis as compared to taking the same amount of carbohydrate and protein without leucine [57]. However, the majority of the research relative to leucine ingestion and protein synthesis has been conducted using animal models. Similar research needs to be conducted in healthy individuals engaging in resistance exercise. aerobic exercise. When BCAAs are taken during aerobic exercise the net rate of protein degradation has been shown to decrease [58]. Equally important, BCAA admin- istration given before and during exhaustive aerobic exer- cise to individuals with reduced muscle glycogen stores may also delay muscle glycogen depletion [59]. When BCAAs were given to runners during a marathon it improved the performance of "slower" runners (those who completed the race in 3.05 h-3.30 h) as compared to "faster" runners (those who completed the race in less than 3.05 h) [60]. Although there are numerous reported metabolic causes of fatigue such as glycogen depletion, proton accumulation, decreases in phosphocreatine lev- els, hypoglycemia, and increased free tryptophan/BCAA ratio, it is the increase in the free tryptophan/BCAA ratio that may be attenuated with BCAA supplementation. Dur- ing prolonged aerobic exercise, the concentration of free tryptophan increases and the uptake of tryptophan into the brain increases. When this occurs, 5-hydroxytryp- tamine (a.k.a. serotonin), which is thought to play a role in the subjective feelings of fatigue, is produced. Similarly, BCAAs are transported into the brain by the same carrier system as tryptophan and thus "compete" with tryp- tophan to be transported into the brain. Therefore, it is believed that when certain amino acids such as BCAAs are present in the plasma in sufficient amounts, it theoreti- cally may decrease the uptake of tryptophan in the brain and ultimately decrease the feelings of fatigue [61,62]. administration taken during prolonged endurance events may help with mental performance in addition to the aforementioned performance benefits [60]. However, not all research investigating BCAA supplementation has reported improvements in exercise performance. One such study [63] reported that leucine ingestion taken before and during anaerobic running to exhaustion (200 sion (100 mg/kg of body weight) did not improve exercise performance. Reasons for discrepant results are not clear at this time, but at the very minimum, it seems apparent that supplementation with BCAAs does not impair per- formance. esses from exercise such as stimulating protein synthesis, aiding in glycogen resynthesis, as well as delaying the onset of fatigue and helping maintain mental function in aerobic-based exercise, we suggest consuming BCAAs (in addition to carbohydrates) before, during, and following an exercise bout. It has been suggested that the RDA for leucine alone should be 45 mg/kg/day for sedentary indi- viduals, and even higher for active individuals [53]. How- ever, while more research is indicated, because BCAAs occur in nature (i.e. animal protein) in a 2:1:1 ratio (leu- cine: isoleucine: valine), one may consider ingesting 45 mg/kg/day of leucine along with approximately 22.5 mg/kg/day of both isoleucine and valine in a 24 hour time frame in order to optimize overall training adaptations. This will ensure the 2:1:1 ratio that appears often in ani- mal protein [64]. It should not be overlooked that com- plete proteins in whole foods, as well as most quality protein powders, contain approximately 25% BCAAs. Any deficiency in BCAA intake from whole foods can easily be remedied by consuming whey protein during the time frame encompassing the exercise session; however, an attempt should be made to obtain all recommended BCAAs from whole food protein sources. Nutrition that exercising individuals need approximately 1.4 to 2.0 grams of protein per kilogram of bodyweight per day. The amount is dependent upon the mode and intensity of the exercise, the quality of the protein ingested, and the status of the energy and carbohydrate intake of the individual. Concerns that protein intake within this range is unhealthy are unfounded in healthy, exercising individuals. An attempt should be made to obtain protein requirements from whole foods, but sup- plemental protein is a safe and convenient method of ingesting high quality dietary protein. The timing of pro- tein intake in the time period encompassing the exercise session has several benefits including improved recovery and greater gains in fat free mass. Protein residues such as branched chain amino acids have been shown to be ben- eficial for the exercising individual, including increasing the rates of protein synthesis, decreasing the rate of pro- tein degradation, and possibly aiding in recovery from exercise. In summary, exercising individuals need more dietary protein than their sedentary counterparts, which can be obtained from whole foods as well as from high |
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