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Supplementing Leucine & BCAAs
Should I Supplement with BCAAs or Leucine?
After learning about how powerful leucine is for body composition and performance, it makes sense to ask - should I supplement with leucine?
Leucine is one of the three “Branched Chain Amino Acids” [BCAAs]. Usually leucine is not supplemented individually, it’s combined with all 3 BCAAs because the biochemical processes concerning muscle protein synthesis require all 3 in a 2:1:1 ratio (Leucine:Isoleucine:Valine).
So the question becomes “Should I use a BCAA supplement?”
Supplementing Leucine & BCAAs
Building muscle is the result of protein accretion exceeding protein breakdown.
While we can increase muscle protein synthesis [MPS], this does not necessarily incur muscle growth. Building muscle requires all amino acids, and it requires that muscle protein synthesis exceeds muscle protein breakdown.
During exercise, the BCAAs are used for fuel, decreasing the levels in our blood. Thus, BCAAs are demonstrably useful for energy, endurance, and performance while stimulating muscle protein synthesis, preventing muscle protein breakdown, and consequently promoting fat loss.
One study found that during caloric restriction combined with exercise, the group consuming a BCAA supplement maintained lean mass and lost fat compared to a control group consuming a carbohydrate placebo, which lost both lean mass and fat mass. (1)
According to Norton & Layman (2), “net protein balance remains negative after resistance exercise, as protein breakdown is greater than protein synthesis, and remains negative until dietary protein or leucine is ingested.”
It seems clear that BCAAs are beneficial for increasing muscle mass, maximizing fat loss, accelerating recovery, and enhancing performance.
However, consider this: the BCAAs are not the only amino acids required to build muscle; all amino acids are required for these purposes, especially the 9 essential amino acids [EAAs], from which the others can be synthesized.
If we do not have adequate levels of these other amino acids in our blood, they will be acquired by muscle protein breakdown.
How, then, have BCAAs shown such positive results?
In the first paper cited, subjects were provided a diet containing an adequate, complete protein source with their meals, for example 5 ounces of chicken. Thus, they presumably had an ample supply of all the essential amino acids in their blood when they were training.
If there’s not an ample supply of the EAAs in our blood & plasma, theoretically, BCAA ingestion would increase demand for the other EAAs and may result in a net decrease of muscle since breakdown would exceed synthesis.
BCAA supplementation will actually breakdown more muscle than it builds?
There are researchers who have reported these findings, especially during fasted states (5).
Wolfe (3) submits that while leucine stimulates muscle protein synthesis [MPS], other essential amino acids [EAAs] are required for actually synthesizing muscle and these amino acids will be acquired via muscle protein breakdown. Thus, muscle protein breakdown will occur at a rate faster than muscle protein synthesis at which point BCAA ingestion will actually decrease muscle protein turnover.
While leucine and the BCAAs may provide energy and stimulate muscle protein synthesis, this increase appears to be transient and BCAA or Leucine supplementation alone are inefficient at best and actually counterproductive at worst.
From the paper: “An extensive search of the literature has revealed no studies in human subjects in which the response of muscle protein synthesis to orally-ingested BCAAs alone was quantified, and only two studies in which the effect of intravenously infused BCAAs alone was assessed. Both of these intravenous infusion studies found that BCAAs decreased muscle protein synthesis as well as protein breakdown, meaning a decrease in muscle protein turnover…. We conclude that the claim that consumption of dietary BCAAs stimulates muscle protein synthesis or produces an anabolic response in human subjects is unwarranted.”
Wolfe raises an important point. More than the BCAAs are required for building and repairing tissue, and they must come from somewhere. If we only supplement with Leucine or BCAAs, where do the other amino acids come from?
This is a controversial position because many have experienced increased performance and accelerated results with BCAAs, and clinical trials have shown their benefits repeatedly.
It seems to be the case that while the full range of EAAs are required for MPS, essential amino acid availability peaks 1.5 to 3 hours after a meal. This is plenty of time for a substantial pre-workout meal. Then we can peak leucine & MPS levels to experience their various benefits. (4)
If we are fasted, however, or many hours from last ingesting a high protein meal containing all EAAs in sufficient quantities (i.e. a Greek yogurt won’t cut it), BCAAs many actually result in more muscle broken down than built.
This is why EAA formulas have become popular more recently, while BCAAs remain popular because EAAs are new and more expensive.
To be fair: if you ingest ample amino acids before you train, as in a high protein meal, you will have adequate amino acids in your blood stream and supplementing BCAAs appears to provide a notable net benefit, in terms of both hypertrophy & performance.
Using BCAAs to supplement a protein source that is deficient in the BCAAs or leucine may also be a wise decision.
However, taking an EAA supplements avoids the potential downfalls of supplementing BCAAs alone by providing as many as all 9 essential amino acids.
Ideally, an EAA supplement will also contain at least 2.5 grams of L-leucine to stimulate MPS, in addition to other EAAs in substantial quantities.
This way, not only do we stimulate MPS, we provide all of the necessary substrates to actually build and repair tissue.
In other words not only do we turn the ignition, we put gas in the tank.
In summary, supplementing an incomplete protein source with BCAAs may be a wise decision. We can also supplement an incomplete protein source with EAAs if it does contain the BCAAs but is missing one of the other EAAs in a significant amount, such as L-methionine or L-lysine.
However, supplementing BCAAs or leucine alone without sufficient amino acids in the blood or during training is inefficient at best and counterproductive at worst because it may increase muscle protein breakdown more than it increases muscle protein synthesis, especially when blood levels of the essential amino acid levels are low as in a fasted state.
To maximize muscle, strength, and fat loss, in general, I personally use a complete essential amino acid supplement during training.
By ingesting pure amino acids in this way, we maximize rate of absorption, which maximizes the amino acid levels in the blood, which maximizes muscle protein synthesis.
In fact, I believe there are other non-essential amino acids and proteins we should include in a pre- or intra-workout supplement, such as L-tyrosine, but that’s a topic of a coming article.
For now, I hope this was helpful.
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Yours in strength,
Daniel J. Furtado, CPT, LMT, Owner of Honor Strength