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supplemental form are whey and casein. Recent investiga- tions have detailed the serum amino acid responses to ingesting different protein types. Using amino acid tracer methodology, it was demonstrated that whey protein elic- its a sharp, rapid increase of plasma amino acids follow- ing ingestion, while the consumption of casein induces a moderate, prolonged increase in plasma amino acids that was sustained over a 7-hr postprandial time period [35]. The differences in the digestibility and absorption of these protein types may indicate that the ingestion of "slow" (casein) and "fast" (whey) proteins differentially mediate whole body protein metabolism due to their digestive properties [35]. Other studies have shown similar differ- ences in the peak plasma levels of amino acids following ingestion of whey and casein fractions (i.e., whey fractions peaking earlier than casein fractions) [36,37]. the differential effects that ingesting different proteins exerts on postprandial blood amino acid responses and muscle protein synthesis after exercise. The data are equiv- ocal relative to which type of protein increases net protein status (breakdown minus synthesis) to a greater extent after exercise. Some research has demonstrated that despite different patterns of blood amino acid responses, muscle protein net balance was similar in those ingesting casein or whey [33]. However, additional research has indicated that whey protein induced protein gain to a greater extent than casein [38]. In contrast, several other studies have shown that casein increased protein deposi- tion at levels greater than whey proteins [35,37]. Nutrition is that individuals engaging in exercise attempt to obtain their protein requirements through whole foods. When supplements are ingested, we recommend that the protein contain both whey and casein compo- nents due to their high protein digestibility corrected amino acid score and ability to increase muscle protein accretion. more dietary protein due to an increase in intramuscular protein oxidation [39] and protein breakdown [40] that occurs during exercise, as well as the need to further com- plement intramuscular protein resynthesis and attenuate proteolytic mechanisms that occur during the post-exer- cise recovery phases [41-43]. Thus, a strategically planned protein intake regimen timed around physical activity is integral in preserving muscle mass or eliciting muscular hypertrophy, ensuring a proper recovery from exercise, and perhaps even sustaining optimal immune function. Previously, high levels of blood amino acids following a in promoting muscle protein synthesis [44]. Evidence is accumulating that supports the benefits of the timing of protein intake and its effect on gains in lean mass during resistance exercise training [45-49]. Given that much of the research to date has been conducted on resistance exercise, more investigations are required to ascertain the effects of protein timing on other modes of exercise. health-related effects associated with post-exercise protein ingestion. A previous investigation utilizing 130 United States Marine subjects [50] examined the effects of an ingested supplement (8 g carbohydrate, 10 g protein, 3 g fat) immediately after exercise on the status of various health markers. These data were compared to 129 subjects ingesting a non-protein supplement (8 g carbohydrate, 0 g protein, 3 g fat), and 128 subjects ingesting placebo tab- lets (0 g carbohydrate, 0 g protein, 0 g fat). Upon the com- pletion of the 54-d trial, researchers reported that the subjects ingesting the protein supplement had an average of 33% fewer total medical visits, including 28% less visits due to bacterial or viral infections, 37% less orthopedic- related visits, and 83% less visits due to heat exhaustion. Moreover, post-exercise muscle soreness was significantly reduced in subjects ingesting protein when compared to the control groups. Previous studies using animal models have demonstrated that whey protein elicits immuno- enhancing properties, likely due to its high content of cysteine; an amino acid that is needed for glutathione pro- duction [51,52]. Hence, previous research has indicated that ingesting a protein source that is rich in essential amino acids and is readily digestible immediately before and following exercise training is beneficial for increasing muscle mass, recovery following exercise, and sustaining immune function during high-volume training periods. While protein ingestion is emphasized in this article, the concomitant ingestion of protein and carbohydrates prior to and/or following exercise has also been shown to be advantageous in increasing muscle protein synthesis; a result which is likely due to an increase in insulin signal- ing following the ingestion of carbohydrates. Nutrition that exercising individuals should consume high quality protein within the time period encompassing their exercise session (i.e. before, during, and after). and valine) constitute approximately one-third of skeletal muscle protein [53]. An increasing amount of literature suggests that of the three BCAAs, leucine appears to play the most significant role in stimulating protein synthesis [54]. In this regard, amino acid supplementation (partic- |
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