|The kids who were the subjects in the study at hand didn’t lift. They ran and cycled and still ended up in a positive nitrogen balance – thanks to post-workout protein supplementation.|
As a SuppVersity reader you are familiar with the results of previous studies investigating the effects of post-workout protein ingestion. Studies that revealed that it takes ~20-30g of whey protein to maximize acute protein synthesis in adults.
In an upcoming issue of the Journal of Applied Physiology researchers from the Nestle Research Center are now about to publish what I believe is a unique study investigating the net protein balance (=synthesis minus breakdown) over 8h and 24h after the workout in response to the ingestion of different amounts of whey + casein (at a 1:4 ratio) immediately after a standardized running and cycling intervention (Moore. 2014)
In contrast to “the average” protein synthesis study, the study at hand didn’t just use an unusual subject group consisting of 6 female and 7 male kids (mean age 11.7 years), the type of exercise and the method the scientists used to determine the usefulness of the low (0.75g/100ml) and high (1.5g/100ml) protein beverages were different as well.
|Figure 1: Graphical overview of the study design (Moore. 2014)|
In view of the recently flaring doubts about the significance of post-exercise acute net protein synthesis as a predictor of training-induced muscle synthesis and the existing evidence that there is no reliable association between the wto (Mitchell. 2014), it is particularly interesting that the team Swiss US, and Canadian researchers measured both, protein breakdown and synthesis, which were calculated by measuring the concentration of the major nitrogen-containing metabolites urea and creatinine were determined in the urine of the subjects, to determine the net protein retention, i.e. the amount of protein that actually remained in the system for 8h and 24h, respectively.
|Overview of the total energy and macronutrient intake (Moore. 2014)|
Strict dietary control is another strength of the study at hand, which was part of a larger investigation the data of which has not yet been published: Participants were provided with a controlled diet for the 24h period during which protein metabolism measures were performed. Resting energy requirements were estimated using standard equations and were corrected with an activity factor of 1.5.
Aside from the energy and macronutrient profiles of the test beverages, the 24h controlled diets were supplied as isoenergetic breakfast and lunch meals (consumed within the laboratory providing ~11 and 40% of 24h energy intake, respectively) and dinner meals (consumed outside the laboratory providing ~35% of 24h energy intake) with the remaining ~14% of energy coming from the test beverages. The breakfast, lunch, and dinner meals were also isoprotein and provided ~15, 45, and 40% of the 24h food protein intake, respectively, with the test beverages providing a variable amount of protein in addition to the meal protein intake.
As you can see in Figure 2 the results were not extremely different from what we already saw in the previously mentioned acute protein synthesis studies. Only the high dose protein supplementation that contained 12.8 ± 3.6 g protein (i.e. 0.32 ± 0.07 g/kg and thus ~25.6g for a 80g human being) supplement established a significantly increase in net protein balance.
|Figure 2: Protein breakdown, synthesis and net protein balance over 24h (Moore. 2014)|
If you take a close look at the left columns of Figure 2 you will even see that the 24h net protein metabolism was in fact slightly negative. Moreover, the study confirms what you’ve previously read here at the SuppVersity an increase in protein availability is – specifically at stable total energy intakes – always associated with an increase in protein breakdown.
Last but not least it may be important to mention that the total protein intake was (a) not extremely different between the three groups (see figure in “tight dietary control” box) and that (b) it was actually below the kids habitual protein intake of 1.56g/kg which would suggest that it is unlikely that some sort of accommodation effect may occur over time.
- de Oliveira, Erick Prado, and Roberto Carlos Burini. “The impact of physical exercise on the gastrointestinal tract.” Current Opinion in Clinical Nutrition & Metabolic Care 12.5 (2009): 533-538.
- Millward, DAVID J., et al. “Effect of exercise on protein metabolism in humans as explored with stable isotopes.” Federation proceedings. Vol. 41. No. 10. 1982.
- Mitchell, Cameron J., et al. “Acute Post-Exercise Myofibrillar Protein Synthesis Is Not Correlated with Resistance Training-Induced Muscle Hypertrophy in Young Men.” PloS one 9.2 (2014): e89431.
- Moore et al. “Post-exercise protein ingestion increases whole body net protein balance in healthy children.” J Appl Physiol (October 23, 2014). Article in press.
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