|Want to maximize net protein retention? Order another one... another steak ;-)|
Whole protein kinetics? Yes, that's different from what you see in the average "whey protein builds muscle study", in which the researchers measure only the fractional protein synthesis. Kim et al. went one step further and measured the protein synthesis (PS), breakdown (PB), and net balance (NB) in their subjects, twenty-three healthy subjects [18 – 40 yrs] who were recruited from the Little Rock area using local newspaper advertisements and flyers posted around the University of Arkansas for Medical Sciences (UAMS) campus and the Little Rock area. Now, it's not like humans had a display you can use to read these variables, so eventually, they were still calculated based on the determinations of the rate of appearance (Ra) into the plasma of phenylalanine and tyrosine, and the fractional Ra of endogenous tyrosine converted from phenylalanine as in a previous study by the same team of researchers (Kim. 2015a). Since this technique is unable to distinguish between the different sites of protein breakdown.and storage, the results of the study at hand could describe increases or decreases in splachnic (=organ) protein synthesis or breakdown, too. It is thus not possible to exclude a null effect on skeletal muscle protein synthesis and breakdown based on the available data.
Whole protein kinetics, two different amounts of protein, with and without exercise
There were yet other things Kim's study had in common with many of the aforementioned "whey protein studies": The study had a run-in that was included to minimize any potential effects of the protein content of the subjects' baseline diets. The subjects ate their high or medium protein meals in the fasted state and the participants - or at least some of them - also trained. To be more specific, the subjects were randomly assigned into an exercise group (X, n=12) protocol consisting of 3 sets of 10 repetitions of bench press, lateralis pull-down, leg press, and leg extension each at 80% of 1 repetition maximum (1 RM, the maximum weight that can be lifted for one repetition) at a pace of 30 sec per set (rest interval between sets was less than 2 min, and the entire exercise bout was completed in ~45 – 50 min), or a resting group (R, n=11).
|Table 1: Overview of the macronutrient intake during the 4-day run-in and the actual experiment (Kim. 2015b)|
- exercise did not significantly affect protein kinetics and blood chemistry, while
- feeding, in general, resulted in a positive net protein balance at both levels of protein intake,
|Figure 1: It's the decrease in protein breakdown, not the marginal increase in protein synthesis that makes the difference between the net protein balance after the high and medium protein meals (Kim. 2015b).|
- Fukagawa, N. K., et al. "Insulin-mediated reduction of whole body protein breakdown. Dose-response effects on leucine metabolism in postabsorptive men." Journal of Clinical Investigation 76.6 (1985): 2306.
- Kim, Il-Young, et al. "Quantity of dietary protein intake, but not pattern of intake, affects net protein balance primarily through differences in protein synthesis in older adults." American Journal of Physiology-Endocrinology and Metabolism 308.1 (2015): E21-E28.
- Kim, et al. "The anabolic response to a meal containing different amounts of protein is not limited by the maximal stimulation of protein synthesis in healthy young adults." Am J Physiol Endocrinol Metab (November 3, 2015b). doi:10.1152/ajpendo.00365.2015.