|Even though the study at hand has been conducted in an endurance training scenario, there's no reason to believe that the superiority of milk protein, the natural mix of whey and casein would be a "cardio-specific" thing. In fact, evidence to the contrary has been discussed previously, here and here.|
In spite of the fact that whey is also the most insulinogenic of these proteins, it is yet also the one that has been shown to "maximize" amino acid oxidation, thereby contributing to a reduction in nitrogen retention (Boirie. 1997; Dangin. 2001). On the other hand, ingestion of CA causes slower but prolonged aminoacidemia and it has the best leucine net balance during the postprandial period (Boirie. 1997; Dangin. 2001), I've discussed in previous articles, such as "Protein Wheysting".
This is where micellar casein (not sodium or calcium caseinate which are fast-, but slower-than-whey-absorbing "damaged" forms of casein, though) comes in. While casein does not produce the same rapid increase in serum amino acid levels it has been shown to cause moderate but prolonged muscle protein synthesis - the exact opposite of whey protein.
|Figure 1: Fractional myofibrillar protein synthesis (A), plasma leucine (B) and plasma insulin (C) levels in young men after ingesting 0.3g/kg whey, casein or a protein-free control drink (Reitelseder. 2011)|
|Figure 2: As a SuppVersity reader you will rememeber that a previous study showed that whey + casein is profoundly more anabolic than whey that is combined with extra BCAAs and glutamine (Kerksick. 2006)|
|Whey (open triangles) increases leucine +protein oxidation vs. casein (closed circles) in man (Boirie. 1997).|
|Table 1: Amino acids in milk (MP), caseinate (CA), whey (WP) and soy (SP) protein (Kanda. 2016).|
In contrast to "the average" study, the Kanda et al. did so in the presence of an endurance, not a strength or no training stimulus at all and used both, the milk-derived proteins caseinate (CA | faster absorbing, non-micellar form of casein), whey (WP) & milk protein (MP) to soy (SP). You can review the individual amino acid composition of all four in Table 1 on the right and will notice that "technically speaking", i.e. judged based on its BCAA content, soy is the "worst muscle builder", whey the "best".
Time for the convenient, but annoying truth(s)!
Truth #1: It's a rodent study! That's convenient for the scientists, because using rodents is cheap and easy, but annoying for us, because rodents are a good model for humans, but only that - a model - and by no means the best one. Since we cannot switch the subjects, though, we have to live with the fact that the subjects in the study at hand were Sprague-Dawley rats with a bodyweight of approximately 150 g (at least there were many | n = 237) who were subjected to a swimming exercise protocol during which they swam for a whopping 2h. Now, where there's shadow, there's also light: The good thing about rodent studies (bad for the rats, though) is, after all, that, much in contrast to humans, rats can be sacrificed after an experiment like that and will thus allow researches to assess the effects of exercise and supplementation with the aforementioned proteins much more accurately than a single or even multiple muscle biopsies.
|Table 2: Macronutrient profile of test proteins; milk (MP), caseinate (CA), whey (WP) and soy protein (SP | Kanda. 2016)|
|Figure 3: Time course of the fractional protein synthesis after endurance exercise with all four proteins (left) and corresponding AUC values (~net protein influx, right | Kanda. 2016).|
- Boirie, Yves, et al. "Slow and fast dietary proteins differently modulate postprandial protein accretion." Proceedings of the National Academy of Sciences 94.26 (1997): 14930-14935.
- Dangin, Martial, et al. "The digestion rate of protein is an independent regulating factor of postprandial protein retention." American Journal of Physiology-Endocrinology And Metabolism 280.2 (2001): E340-E348.
- Kanda, Atsushi, et al. "Effects Of Whey, Casein, Or Milk Protein Ingestion On Muscle Protein Synthesis After Endurance Exercise." MEDICINE AND SCIENCE IN SPORTS AND EXERCISE. Vol. 46. No. 5. 530 WALNUT ST, PHILADELPHIA, PA 19106-3621 USA: LIPPINCOTT WILLIAMS & WILKINS, 2014.
- Kerksick, Chad M., et al. "The effects of protein and amino acid supplementation on performance and training adaptations during ten weeks of resistance training." The Journal of Strength & Conditioning Research 20.3 (2006): 643-653.
- Norton, Layne E., et al. "The leucine content of a complete meal directs peak activation but not duration of skeletal muscle protein synthesis and mammalian target of rapamycin signaling in rats." The Journal of nutrition 139.6 (2009): 1103-1109.
- Reitelseder, Søren, et al. "Whey and casein labeled with L-[1-13C] leucine and muscle protein synthesis: effect of resistance exercise and protein ingestion." American Journal of Physiology-Endocrinology and Metabolism 300.1 (2011): E231-E242.