Muscle loss with aging is one of the inescapable characteristics of growing older. While age-related muscle loss is a normal part of the aging process, we can temper its effect with the nutritional support of essential amino acids (EAAs).
Anabolic Resistance in Aging
Muscle loss with aging occurs because as the years wear on we lose the ability to make new muscle protein from dietary protein. The impaired ability to build new muscle protein is called anabolic resistance.
When your body enters an anabolic resistant state it has trouble getting the “motor” started. The starter for the motor, in this case, is a factor inside the muscle cells called mTOR. mTOR starts the whole process of protein synthesis. The activation of mTOR begins a cascade of responses that ultimately result in the initiation of protein synthesis. Together these responses are called initiation factors.
In aging muscle, the reactivity of mTOR and the other initiation factors are blunted, and this is a basis of anabolic resistance.
The Importance of the Essential Amino Acid Leucine
Leucine is an EAA that is called a branched-chain amino acid because of its chemical structure. Leucine is one of the most important dietary regulators of mTOR activity. If the proportion of leucine in an EAA mixture is increased to an amount that exceeds its normal contribution to the composition of dietary protein, the EAA supplement can effectively activate mTOR in aging muscle.
However, leucine alone is not enough. All the essential amino acids need to be present in the proper proportion to produce new muscle protein. You can think of leucine as the quarterback of a football team—it may be the pivot point of how the team performs, but without the other players the team is not going to have much success.
The Other 8 Essential Amino Acids
When you consume a large amount of the EAA leucine, you increase the rate at which leucine gets broken down since the body is designed to maintain steady levels of EAAs. Coincidentally, the breakdown of the other essential branched-chain amino acids (the BCAAs valine and isoleucine) is also increased because the same enzyme works on all three. Consequently, the proportions of valine and isoleucine in an EAA formulation containing abundant leucine must be increased.
Lysine is another EAA with distinct characteristics—it is not transported into muscle as readily as other EAAs are. For this reason, the optimal profile of EAAs to maximally stimulate “anabolic resistant” muscle includes proportionately more lysine than is reflected in the composition of muscle protein. So, even though it may seem logical to provide EAAs for a muscle-building supplement in a profile similar to the makeup of muscle, adjustments can be made to boost the signal and improve delivery of amino acids to overcome “anabolic resistance.”
The other five EAAs—phenylalanine, threonine, methionine, tryptophan, and histidine—also need to be included in a mixture of EAAs to maximally stimulate muscle protein synthesis. The proportionate contribution of these additional EAAs must be reduced below what occurs in muscle protein because of the necessity of including disproportionately high amounts of BCAAs and lysine.
Do EAAs Work for Muscle Loss with Aging?
Well, let’s see what science has to say.
Anabolic resistance in elderly subjects was resolved when a mixture of EAAs meeting the criteria outlined above was provided. The mixture of EAAs was three times more effective at stimulating muscle protein synthesis in older individuals on a gram-per-gram basis than was whey protein isolate, which is a very high-quality protein by traditional means of assessment.
Another study showed that a specifically formulated EAA supplement decreased loss of muscle mass and strength that occurs with bed rest and recovery from hip replacement.
And yet another amino acid study demonstrated that daily supplementation with EAAs improved muscle mass and function in healthy, active elderly women as well.
The difference between the effectiveness of EAAs and intact protein cannot be made up just by consuming more of the intact protein, because the optimal profile of EAAs will never be achieved with intact protein. You can learn more about dietary protein vs. EAA supplements here.
What’s the quick takeaway? When it comes to amino acids for muscle loss with aging, it’s a matter of quality, not quantity.