When you eat protein it is digested and absorbed into the blood as
. One of the questions that remain unclear is the effect of rate of digestion/absorption of proteins. One of the clear distinctions between
is the digestion rate. Whey is absorbed quick resulting in rapid increases in important blood amino acids, whereas casein results in a slow and steady release of amino acids into the blood. Studies have compared whey versus casein with mixed results but generally favoring whey.
But in addition to differences in rate of absorption they also differ in amino acid content. So Canadian researchers performed a clever experiment whereby they had healthy men ingest
post-resistance exercise in either a bolus (a single 25 gram dose) or pulsed (2.5 grams every 20 min) pattern. Thus they received the exact same amount of protein containing the exact amino acids, but during the pulse trial simply sipped the whey drink spacing it out over a 3 hour period. As expected the bolus trial resulted in a spike in blood levels of amino acids including leucine, whereas pulse resulted in a more sustained and prolonged in blood amino acids. The rate of muscle protein synthesis determined over 3 hr post-exercise was significantly greater with bolus (95%) than pulse (42%). Surprisingly, greater protein synthesis was also present 3-5 hr after exercise in bolus (193%) than pulse (121%). In conclusion, it may be wise to emphasize slow absorbing forms of carbohydrate that release glucose slowly, but when it comes to protein it appears from this latest research that it's better to get a spike in blood levels of amino acid by ingesting rapidly absorbed forms of protein in a bolus.
West DW, Burd NA, Coffey VG, Baker SK, Burke LM, Hawley JA, Moore DR, Stellingwerff T, Phillips SM. Rapid aminoacidemia enhances myofibrillar protein synthesis and anabolic intramuscular signaling responses after resistance exercise. Am J Clin Nutr. 2011 Jul 27.