In the sports nutrition industry, there is a gradual shift to using hydrolyzed proteins for their increased speed of absorption and inducing hyperleucemia and hyperinsulinemia, conditions that may promote a faster and greater response to recovery and skeletal muscle growth. A recent paper by Deglaire et al. confirms this is the case for casein protein, however it also reveals other important effects.
Because of opioid peptides in the intact casein, intestinal transit time is greater compared to the hydrolysate. As expected, aminoacidemia was faster with the hydrolysate, and they also found a higher initial urea production, corroborating other research. This may be a mechanism to try to prevent the acute hyperaminoacidemia from large amino acid boluses.
Overall, net postprandial protein utilization was similar between the 2 groups, but they found that nitrogen from intact casein was incorporated more into perpipheral tissues and less into splanchnic tissues, while hydrolysate was less and more, respectively. The differences do not seem to be large enough to have a long term disadvantage, and the groups were 8 hours fasted after the test meal. For athletic purposes, hydrolyzed protein still seems superior (other research seems to corroborate which will be reviewed in other posts), and the increased insulin from hydrolyzed protein is more anti-catabolic compared to intact. Hydrolyzed whey, for example, in research earlier this year has been found to maximize net protein synthesis because of the insulinotropic response. Much of this is of course moot when you factor in other nutrients from meals in a non fasted state.
But hydrolyzed protein is used clinically for patients with digestive problems, and given to infants in formula. It is still possible that a real world, long term effect of a more positive skeletal muscle nitrogen balance may be seen in future research with intact proteins.
Deglaire A, Fromentin C, Fouillet H, Airinei G, Gaudichon C, Boutry C, Benamouzig R, Moughan PJ, Tomé D, & Bos C (2009). Hydrolyzed dietary casein as compared with the intact protein reduces postprandial peripheral, but not whole-body, uptake of nitrogen in humans. The American journal of clinical nutrition PMID: 19692493