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| Image 1: Without the other essential amino acids (EAAs), the branched chain amino acids, leucine, isoleucine and valine (BCAAs) have nothing to "build" your muscle from ;-) |
Usually, I do not get very excited, when I hit upon another study into the "protein-synthetic response" that is triggered by the ingestion of branched chain amino acids (BCAAs). I mean, let's be honest...
we all know that their ingestion will trigger the phosphorylation of the mammalian target of rapamycin and thusly increase protein synthesis, so why would we need another study where instead of a 17.5% increase in protein synthesis, we would see a 18.3% increase? Actually, we don't... the data Marcus Borgenvik, William Apró and Eva Blomstrand from the
Åstrand Laboratory, Swedish School of Sport and Health Sciences and the
Karolinska Institutet, in Stockholm, Sweden (
Borgenvik. 2011), collected goes yet well beyond what we have seen in most of the previous studies and is thus well worth an individual blogpost here at the SuppVersity.
BCCAs work! How? Little do we know...
If we are honest, we must concede that
our (=the scientific) understanding of the complex processes that are triggered when "large" amounts of BCAAs hit our bloodstream, is very limited. What we know is that we can measure increases in mTOR-expression that correlate with likewise measurable increases in protein synthesis. What we do not really know is how exactly one leads to the other and where the influences of amino acid supplementation and exercise training overlap. This is even more true for the complementary side of the protein synthetic equation of which Borgenvik et al. state that
[w]hereas extensive evidence for the stimulatory effect of amino acids, either alone or in
combination with exercise, on protein synthesis has been reported, their effect on protein
breakdown is elusive.
In that, it is particularly confusing that "previous investigations involving ingestion of essential amino acids
(EAA) in connection with resistance exercise have revealed no attenuating effect on protein
breakdown", while studies which investigated the effect of BCAA or leucine in isolation, report reduction in protein degradation in subjects at rest or performing eccentric endurance exercise (
MacLean. 1994). Reason enough for the Swedish scientists to recruit a group of
seven healthy, recreationally active participants (5 men, 2 women; 27 (± 2) years; height 175 (± 5) cm; weight 67 (± 7) kg), put them on a
standardized diet (17% protein; 25% fat; 57% carbs; ~2100kcal for women, ~2700kcal for men) for two days and, on the subsequent morning (subjects reported to the lab fasted) and after a thorough warm-up, have them perform
- 4 sets of 10 repetitions at 80% of their predetermined 1 RM, followed by another
- 4 sets of 15 repetitions at 65% of their 1 RM of single-legged leg presses.
The subjects used
the same leg on all exercises and rested ~5min after each set. Before the warm-up, during and immediately after and 15 and 45min after the exercise regimen the subjects consumed either
- 150 mL of BCAAs (2:1:1 ratio) in flavored water, or
- 150 mL flavored water alone.
The
total amount of BCAAs was 85mg/kg or 5.695g for the "average" study participant. After four weeks the experiment was repeated with each participant receiving the opposite treatment.
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| Figure 1: Complete analysis of serum amino acid levels in the trained and untrained leg of subjects receiving BCAA or Placebo supplement before, during and after the completion of a standardized single-legged leg press exercise (data adapted from Borgenvik. 2011) |
As far as the study protocol goes this is thus certainly not an extraordinary study. If you take a look at figure 1, where I deliberately plotted
all the data the scientists gathered as far as serum amino acid concentrations are concerned, you will yet realize that
what makes this study stand out is the sheer amount of parameters Borgenik et al. have analyzed. Similar data is also available for the amino acid concentrations in the exercised muscle and though, the scientists, who set out to investigate the effects of BCAA supplementation on protein breakdown, would probably disagree with me, here, I feel that this data actually has the most real world significance for physical culturists, like you and me.
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| Figure 2: Relative increase / decrease in intra-muscular BCAAs and other EAAs in BCAA supplemented subjects vs. placebo control at different time-points before, during and after single-legged leg presses (data adapted from Borgenvik. 2011) |
After all, a brief glance at the effects the ingestion of ~6g of BCAA had on the respective tissue levels of leucine, isoleucine and valine (figure 2, BCAA) and the other, "missing" essental amino acids (figure 2, EAA - BCAA) should suffice to understand that though BCAAs may be the necessary to trigger protein synthesis, they are yet obviously
not sufficient to "build muscle" - or how else would you explain the
pronounced reduction in the concentration of the aromatic amino acids, tyrosine and phenylalanine, in both plasma and muscle as well as muscle EAA (BCAA excluded) during the recovery period
Borgenik et al. observed in their study? The scientists at least conclude that
[s]ince tyrosine and phenylalanine are neither synthesized nor degraded in skeletal muscle, reduction in the levels of these amino acid could be indicative of an improved net muscle protein balance, i.e. an enhanced rate of synthesis and/or decreased rate of breakdown [and] could be explained by incorporation into protein.
The accrual of muscle mass (whatever that may eventually mean, cf.
yesterday's installment of the
Intermittent Thoughts) thusly obviously relies on the
presence of all essential amino acids and not just the "branched chained holy grail" of protein synthesis, of which the current study revealed that they (BCAA ingestion)
reduced the expression of MAFbx, which regulates the protein transcription factor MyoD and the eukaryotic initiation factor-3f (eIF-3f), which, in turn is of importance in the mTOR-p70S6k signaling pathway, by 30% and 50% in the resting and exercising legs, respectively.
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| Figure 3: Relative (compared to placebo) mTOR and p70S6K phosphorylation in response to BCAA supplementation in exercised (EX) and non-exercised (Rest) leg at different time-points before, and after single-legged leg presses (data adapted from Borgenvik. 2011) |
As figure 3 finally goes to show, we see
the "usual" increases in mTOR and p70S6K phosphorylation that are commonly held responsible for the downstream increases in protein synthesis, and which were obviously more pronounced in the exercised compared to the non-exercised leg. The latter may be ascribed to what the scientists cautiously label a ...
[...] tendency for BCAA supplementation to attenuate the elevation in the level of Rheb mRNA in both resting (1.7-fold under the placebo versus 1.2-fold in the BCAA condition) and exercising muscle (2.4-fold versus 1.5-fold).
This ameliorative effect on Rheb, the low-molecular weight GTPase located immediately up-stream of mTOR, in combination with the exercise induced reductions in REDD2 expression (another negative regulator of mTOR) the scientists observed in the exercised leg are actually where we are currently at, as far as our understanding of the complex protein synthetic machinery goes. It is here at the gene-level where
amino acid supplementation and its effect on Rheb and exercise and its effect on REDD synergize and facilitate those muscle gains trainees have been making for years often
without any understanding of the biological underpinnings.
And though we may eventually be able to squeeze out another 5-10% more muscle mass, when we eventually get the "whole picture",
I seriously doubt that even the most thorough understanding of the underlying biomolecular processes will change such basic recommendations as "take your 25g of fast digesting whey as a bolus immediately post workout" (cf. "
Never Sip Your Whey!") - or what would you say?
