BCAA is a common, if not the go-to supplement to stop muscle catabolism when training fasted. It’s also used as an intra-workout supplement for the same reason or to boost hypertrophy afterwards.
BCAAs are not only used to suppress catabolism but also to promote anabolism post-workout. Research shows that when amino acids are consumed pre-workout promotes greater muscle protein synthesis than when amino acids are only provided post-workout.
The question for the article is:
Should BCAAs, as a source of amino acids, even be used to prevent catabolism and promote anabolism?
In short: there are 9 essential amino acids (EAAs) and 11 non-essential amino acids (NEAAs). The body is able to make the NEAAs from the EAAs so actually just requires the EAAs to promote muscle protein synthesis (MPS) and anabolism. There are certain NEAAs that are now considered conditionally essential, such as glycine and taurine, because under certain conditions the demand for these amino acids are higher than what is received from the diet or that is synthesized, so supplementing them provides lots of benefits. But this article is not to talk about them.
When fasted, muscle protein breakdown (MPB) is 30% greater than MPS and amino acids are released from the muscles or other fat-free tissue. About 70% of those amino acids are reused for muscle protein synthesis and the rest is used for de novo gluconeogenesis, the creation of neurotransmitters, obligatory oxidation (burned for energy in the Kreb cycle), etc.
In the fed state MPS is increased and MPB decreased, thus the net protein balance is tilted to positive to a point where you can build muscle.
The used of BCAAs, which provides only 3 of the EAAs, will only transiently stimulate MPS (mTOR) by utilizing endogenous stores of the other precursors of protein synthesis. However, endogenous stores of amino acids, such as those in plasma and free intracellular pools, are quite limited and may quickly become depleted. If the stimulation of protein synthesis cannot be sustained, there is little physiological significance. Meaning, the balance will not tilt to a net positive. No new muscle will be created. You need a surplus of all 9 EAAs to build muscle. When you give a surplus of only 3, but lack 6, you cannot form new muscle tissue, because there is still 6 missing. Capisce?
Similarly, insulin is a potent activator of the anabolic signalling pathways, but this fails to increase muscle fractional synthesis rate (FSR) because of a deficiency of EAAs. Conversely, consumption of a small amount (3 g) of EAAs stimulates muscle protein synthesis without affecting initiation factor activity e.g., Akt, S6 kinase, and 4E–BP1 (R). Interestingly, EAAs were more effective at stimulating MPS than BCAAs (R).
Even adding BCAAs to carbs does not promote hypertrophy more than just the carbs alone or halt catabolism to a greater extent (R). Adding all 9 EAAs does however.
The only situation where BCAAs are actually of use is when BCAAs are added to a low protein meal. For example, the addition of 5g of BCAAs to a beverage containing 6.25g whey protein increased muscle protein synthesis to a level comparable to that induced by 25g of whey protein (R). But adding BCAAs to a 25g serving of whey doesn’t increase MPS or hypertrophy to a greater extent.
BCAAs does slow down catabolism, but cannot do so completely or stimulate the growth of new muscle unless the other EAAs are also provided.
I’d advise, when optimal hypertrophy is the goal, to ingest EAAs rather than BCAAs pre-workout. Although there aren’t any studies to prove it yet, it will be at least equally effective as BCAAs at lowering catabolism and at best, do a better job at it. It also provides all the EAAs needed for hypertrophy, which would potentiate post-workout hypertrophy more than when only the BCAAs are taken.
The only downside to taking EAAs are that it’s more expensive than BCAAs to get the same amount of leucine.
You can still take BCAAs if you want, just eat lots of good quality protein afterwards to supply all the amino acids needed for proper hypertrophy.