Originally Posted by Swifto
Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscl
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J Appl Physiol. 2009 Sep;107(3):987-92. Epub 2009 Jul 9.
Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men.
Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA, Phillips SM.
Department of Kinesiology-Exercise Metabolism Research Group, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
This study was designed to compare the acute response of mixed muscle protein synthesis (MPS) to rapidly (i.e., whey hydrolysate and soy) and slowly (i.e., micellar casein) digested proteins both at rest and after resistance exercise. Three groups of healthy young men (n = 6 per group) performed a bout of unilateral leg resistance exercise followed by the consumption of a drink containing an equivalent content of essential amino acids (10 g) as either whey hydrolysate, micellar casein, or soy protein isolate. Mixed MPS was determined by a primed constant infusion of l-[ring-(13)C(6)]phenylalanine. Ingestion of whey protein resulted in a larger increase in blood essential amino acid, branched-chain amino acid, and leucine concentrations than either casein or soy (P < 0.05). Mixed MPS at rest (determined in the nonexercised leg) was higher with ingestion of faster proteins (whey = 0.091 +/- 0.015, soy = 0.078 +/- 0.014, casein = 0.047 +/- 0.008%/h); MPS after consumption of whey was approximately 93% greater than casein (P < 0.01) and approximately 18% greater than soy (P = 0.067). A similar result was observed after exercise (whey > soy > casein); MPS following whey consumption was approximately 122% greater than casein (P < 0.01) and 31% greater than soy (P < 0.05). MPS was also greater with soy consumption at rest (64%) and following resistance exercise (69%) compared with casein (both P < 0.01). We conclude that the feeding-induced simulation of MPS in young men is greater after whey hydrolysate or soy protein consumption than casein both at rest and after resistance exercise; moreover, despite both being fast proteins, whey hydrolysate stimulated MPS to a greater degree than soy after resistance exercise. These differences may be related to how quickly the proteins are digested (i.e., fast vs. slow) or possibly to small differences in leucine content of each protein.
For example, several studies have noted that “fast” proteins stimulate a
large rise in protein synthesis whereas “slow” proteins primarily
inhibit protein breakdown, but these results come from data
at the whole body level of which muscle comprises
only 25% and turns over at a much slower rate than, for
example, gut proteins. In addition, milk proteins
appear to support greater “peripheral” (i.e., muscle) vs.
splanchnic protein synthesis than do soy proteins.
Interestingly, when examining whole body leucine kinetics, prior studies actually found that casein consumption promoted a higher whole body leucine
balance than whey. While these findings may seem
contradictory to what we observed here, the inhibitory effect of
casein on protein breakdown, almost certainly in the splanchnic
region, was the largest contributor to the greater
whole body leucine balance observed.
In addition, the increase in whole body protein synthesis stimulated by whey was observed to be quite transient.
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