Thursday, June 4, 2015

Lactose, Fat & Other Proteins Impair Digestion of Micellar Casein W/Out Modifying Protein Synthesis or Breakdown

It does not necessarily have to be supplemental micellar casein. Quark, for example, is an excellent casein source you can use in "smoothies".
As a SuppVersity reader you are well aware of the interactions between casein micelles and the low and high pH milieu of the intestinal tract. They clump and form a mass that is significantly harder to digest than the easily digestible albumin proteins from whey.

As discussed in previous articles you can use this property of casein to your advantage, an advantage that makes the combination of whey and casein protein so efficient in terms of its ability to (a) boost protein synthesis (that's what the whey fraction will do) and (b) sustain the elevated protein synthesis (this is what the slowly digesting casein micelles will do).
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Even when it's used on its own, though, casein protein is a very useful muscle builder, one of which we didn't know yet whether its efficacy would be impaired by the co-ingestion of the co-factors in milk, i.e. lactose, whey proteins, fat, and minerals would affect the digestion and effects of casein. More specifically, the scientists from the NUTRIM School of Nutrition and Translational Research in Metabolism in Maastricht speculated that the ingestion of casein in a milk matrix would trigger a "more rapid casein digestion and amino acid absorption, greater amino acid availability, greater whole-body protein accretion, and greater postprandial muscle protein synthesis when compared to the ingestion of isolated casein dissolved in water" (Churchward-Venne. 2015).

Table 1: Subject characteristics of healthy older men who ingested 25-g intrinsically labeled casein with or without milk serum | Values are means 6 SEMs, n = 16 (Cas and Cas+Serum). No significant differences were observed between groups. Cas, casein; Cas+Serum (Churchward-Venne. 2015).
To test this hypothesis that could be of great importance for both athletes and older adults, who are at risk of sarcopenic muscle loss, the Dutch researchers recruited thirty-two healthy older men (aged 71 +/- 1 y) and conducted a parallel-group, randomized controlled trial during which the subjects received either 
  • 25 g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine labeled casein dissolved in bovine milk serum (Cas+Serum | the serum contained ~10.3% lactose, ~0.3% protein, ~0.06% fat, and ~1.1% minerals), or
  • 25 g of the same casein mixed with plain water (Cas)
to assess the effects of the milk matrix on casein protein digestion and absorption kinetics and postprandial muscle protein synthesis.
The problem with casein studies is that most of them use fast digesting, "non-clumping" calcium or sodium caseinates. That's also the case for the dozens of rodent studies that claim that casein was pro-carcinogenic and what-not and it's in contrast to the studies I referred to in the introduction of this article and the study at hand. Speaking of which: I am not sure how realistic the use of milk serum and casein protein is - I mean, I'd have preferred the use of casein alone and casein + meal. This would have been a much more realistic litmus test, because the 25g casein + small quantities of lactose, fat, and other milk proteins mix used in the study at hand is not exactly close to milk or anything else you'd usually eat.
The results of the experiment falsified the scientists' assumption that the addition of a milk matrix to isolated casein would result in a more rapid casein digestion and amino acid absorption, a more rapid increase in plasma amino acid availability, and subsequently greater postprandial whole-body protein accretion as well as skeletal muscle protein synthesis when compared to the ingestion of isolated casein without a milk matrix (i.e., dissolved in water).
Figure 1: Plasma tyrosine (left, top), and leucine (left bottom) concentrations (micromoles per liter), as well as protein breakdown and synthesis (right) during basal postabsorptive conditions and after ingestion of 25-g intrinsically labeled casein with or without milk serum in older men (Churchward-Venne. 2015)
If you look at the data, it is actually rather the opposite that happened: The provision of the "missing" nutrients from milk slows the digestion of casein micelles (it is possible that the total amount of protein that was absorbed is identical, but the 300 min study period does not allow for a confirmation of this hypothesis). The slower protein digestion did yet not have a negative effect on the post-prandial protein synthesis; so, there's certainly no evidence of the increase in protein anabolism Churchward-Venne et al. (2015) expected, but there's no evidence of detrimental effects, either.

Thus, if neither protein breakdown nor synthesis are influenced, the results of the study at hand suggest that another often advertised supplement "quality", i.e. maximal digestion speed, is practically irrelevant  if you get enough protein per serving.
When it Comes to its Satiety Effect, More Protein Doesn't Help More - Athletes Trying to Lose Weight May Fare Better if They Spread Their Intake to Several 20-30g Servings | more
Bottom line: The fact that neither protein breakdown nor synthesis were significantly different clearly indicates that it does not really matter if you consume your micellar casein pure or together with its natural synergists.

Very similar results have previously been observed for the combination of whey protein and micellar casein, where the addition of the slow-digesting casein proteins do not, as some people may expct, reduce the protein-anabolic effects of whey protein - which is, at least in part, why the combination of the two is such an outstanding muscle builder for athletes.

As I already hinted at in the red box, the study I am still waiting or is not the one the Dutch scientists conducted. The study I would like to see is one that test whether there's a difference between the pro-anabolic effects of whey protein alone and whey protein consumed along a complete meal. I don't really expect to see a physiologically relevant difference, but who knows - without experimental verification that's nothing but my personal hypothesis | Comment on FB!
References:
  • Churchward-Venne, Tyler A., et al. "Ingestion of Casein in a Milk Matrix Modulates Dietary Protein Digestion and Absorption Kinetics but Does Not Modulate Postprandial Muscle Protein Synthesis in Older Men." The Journal of Nutrition (2015): jn213710.