In this blog post, Dr. Bucci explains how the steady supply of amino acids in EFS and EFS-PRO support the immune system during periods of strenuous, long-term exercise when supply is low, demand is high, and the immune system is actively uptaking and consuming amino acids.

Days Lost are Days Weaker

For endurance athletes, maintaining immune system health is important for keeping up a training and competition schedule – especially when your body is taxed through constant cycles of exhaustion and recovery. Hundreds of human studies of exercise and immune function have revealed that pushing your limits, overstepping your boundaries from intense exercise, and continuously training will stress your immune system and decrease its overall functions in many ways.

To perform your best, you need to keep training consistently without gaps caused by not feeling 100% or feeling under the weather. The more you exercise, the more your immune system needs to keep up, though, so maximal exercise puts you more at risk for lost time and decreased performance. Naturally, any endurance nutrition worth its salt will want to address that, and EFS and EFS-PRO do it through the inclusion of amino acids.

Amino Acids & Immune Function

your immune system operates differently from muscles, nerves, and other organs; it uses amino acids as energy

We typically associate amino acids with rebuilding muscles and post-training recovery, so why are amino acids important for immune function? Because your immune system operates differently from muscles, nerves, and other organs; it uses amino acids as energy, even preferring them to glucose and fats.

The immune system’s major amino acid fuels are glutamine and the branched-chain amino acids leucine, isoleucine, and valine, which we’ll just lump together as BCAAs for this blog. Because of their known importance for immune cells, research has focused on these amino acids and immune function in long-term, strenuous exercise.


Glutamine is the most abundant amino acid in the body, accounting for greater than 60% of the total intramuscular free amino acid pool. Virtually every cell in the body constantly uses glutamine for very important functions critical to life. Some tissues rely heavily on glutamine as fuel instead of glucose – immune cells and GI tract lining cells in particular. Glutamine and BCAAs help immune cells maintain their healthy functions during exercise, especially supporting upper respiratory tract health.

Glutamine is so important to your body that your body cannot afford to rely solely on dietary intake because it might run out – with dire, potentially deadly consequences. It’s that important. You need a certain amount of glutamine, or else.

Despite its foundational importance, glutamine has long been considered a “dispensable amino acid because the body has the ability to produce it. That simply means if it does not get it through the diet, the body has a mechanism to produce some glutamine from other amino acids (mostly BCAAs).

Branched-Chain Amino Acids

BCAAs are your body’s back door way to make more glutamine during times of increased need. But like glutamine, intense, long-term exercise can deplete body levels of BCAAs. BCAAs are cannibalized into making energy compounds (glucose and ketoacids) when exercise is intense, and their levels in blood decrease. BCAA supplements have been shown in human studies to maintain normal glutamine levels, especially when given during exercise, not before or after.

Peak Demand

Prolonged exercise lowers blood plasma glutamine levels.

Even when glutamine is being made endogenously with BCAAs, a mountain of evidence demonstrates that, during times of physical stress, the body cannot produce enough to keep up with demand. Furthermore, molecular signals targeting other systems during exhaustive exercise are also seen by immune system cells, and they immediately become activated, which can be counterproductive by consuming existing amino acid supplies. Prolonged exercise lowers blood plasma glutamine levels and prompts increased consumption, creating peak demand through paucity.

From much research, lowered blood plasma glutamine levels have shown a suppressive effect on immune function, which is an excellent reason for timely supplementation with L-glutamine during strenuous exercise, when need becomes acute. This is so common it has a name in the scientific literature – The Glutamine Hypothesis. More glutamine good, less glutamine bad.

…and Timely Supply

Amino acids do not support immune function as well when taken before or after exercise, because they are frittered away quickly in other non-immune tissues (especially the liver) and converted to other amino acids, energetic compounds (ketoacids, for example), glucose, fat or downstream metabolites (like neurotransmitters). This frittering away of amino acids is rapid, within the time it takes to complete an endurance event, and so rapid that the amino acids are not around or already spoken for (metabolically speaking) so that your immune system, not yet having a need before exercise, is not going to consume them.

That’s why, after exercise, immune cells have less amino acid fuel and more competition for amino acid uptake, and thus, end up not being as healthy as they could be. But during exercise, your immune cells are signaled to be ready for anything to fight the stress of exercise, so they load up on glutamine and BCAAs.

The Glutamine Hypothesis in Action

the key to using amino acids to support immune system function is to take them during exercise

Given the discrepancy in supply and demand during exercise, the key to using amino acids to support immune system function is to take them during exercise. So The Glutamine Hypothesis is best applied in literal action – while you’re training, your blood plasma glutamine levels are decreased, and your immune system is actively seeking more fuel. In fact, this is why some human clinical studies have not found big effects on immune function from amino acids – they did not take into account the physiology of the immune system and timing of amino acid fluxes (movements around the body) during exercise.

But your immune system does not care about scientists kicking and screaming at each other about the minutiae of research methodology; it just wants glutamine and BCAAs continuously during exercise to do its job and keep you healthy. The amounts of amino acids in EFS and EFS-PRO have been fine-tuned to maintain a steady supply at peak uptake periods during long-term exercise, addressing the low supply/high demand discrepancy of amino acids when your immune system wants them most.

August 17, 2021 — Luke Bucci

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