Int J Food Sci Nutr. 2008 May 8:1-11. [Epub ahead of print] Links
Plasma amino acid response after ingestion of different whey protein fractions.Farnfield MM, Trenerry C, Carey KA, Cameron-Smith D.
School of Exercise and Nutrition Sciences, Deakin University, Burwood, Victoria, Australia.

Background and objectives
The digestion rate of proteins and subsequent absorption of amino acids can independently modulate protein metabolism. The objective of the present study was to examine the blood amino acid response to whey protein isolate (WPI), beta-lactoglobulin-enriched WPI, hydrolysed WPI and a flavour-identical control.
Methods
Eight healthy adults (four female, four male) were recruited (mean+/-standard error of the mean: age, 27.0+/-0.76 years; body mass index, 23.2+/-0.8 kg/cm(2)) and after an overnight fast consumed 500 ml of each drink, each containing 25g protein, in a cross-over design. Blood was taken at rest and then every 15 min for 2 h post ingestion. Results
Ingesting the beta-lactoglobulin-enriched WPI drink resulted in significantly greater plasma leucine concentrations at 45-120 min and significantly greater branched-chain amino acid concentrations at 60-105 min post ingestion compared with hydrolysed WPI. No differences were observed between WPI and beta-lactoglobulin-enriched WPI, and all protein drinks resulted in elevated blood amino acids compared with flavour-identical control.
Conclusions
In conclusion, whole proteins resulted in a more rapid absorption of leucine and branched-chain amino acid into the blood compared with the hydrolysed molecular form of whey protein.