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When used correctly, branched-chain amino acids (BCAAs) help improve exercise performance after hours of grueling effort. Late in the race, deep in the training session – those times when you need an extra reserve of energy the most. But as that “when used correctly” qualifier suggests, it’s not as simple as loading up on BCAAs. Getting the full benefit of a late-race boost requires certain conditions to be met.

In this blog post, Dr. Bucci works through those conditions, explaining how EFS and EFS-PRO deliver BCAAs at the correct time, under the correct circumstances, and at the correct dose in order to reinforce flagging reserves when you’ve already been in the red for hours but there’s still more work to do.


  1. BCAAs are in EFS & EFS-PRO because they go straight to energy when glycogen stores are low during latter stages of long-duration, exhaustive exercise.
  2. Recent metabolomic human studies show BCAAs are used to make energy cycle metabolites.
  3. BCAAs are sacrificed for energy when muscle glycogen stores are being used up.
  4. BCAAs signal expansion of energy production from fats and amino acids when glycogen stores are low.


BCAAs and L-Glutamine have always been in EFS and EFS-PRO, because human clinical research showing benefits for performance by multiple mechanisms of action has always said it should be there. Those studies also taught us the trick for getting the most out of BCAAs, which net huge performance under certain conditions; however, arm-chair researchers have generally disregarded BCAAs for exercise because a simple review of human studies of BCAA supplementation has not met the conditions for success, namely:

  1. Exercise needs to be strenuous – nearing the end of your rope, about to bonk, running out of gas.
  2. BCAAs need to be taken during and throughout long-duration exercise – NOT an hour before or once/twice daily for weeks before.
  3. Taking a big blast of BCAAs (5 or more grams) was not always helpful, so an effective dose was elusive.


So why aren’t BCAAs more common across the endurance industry? Because – as is so often the case – a lack of understanding of what BCAAs are really doing during exercise has led to most human BCAA studies missing the mark for finding benefits. The issue is largely because of when BCAAs were administered during exercise: too early.

Most – if not all – of the BCAAs supplemented before exercise are not there anymore when they can make a difference. Even taking BCAAs an hour before exercise is too far away from that late-exercise point when you need them. They are simply burned up to get rid of them, because when you begin exercising, you already have plenty of carbs stored and your energy demands are not stressed until much later.

If BCAAs are taken before you’ve begun to dip into your glycogen carb reserves, it’s like you never took them, which is just like a placebo. That’s a misguided study design that only reinforces null results vs. placebo, leading to a misguided consensus that BCAAs don’t impact exercise – a classic case of BCAA GIGO (garbage in; garbage out).


So how did we figure out BCAAs are good for late-race energy? Because we tested them in EFS & EFS-PRO, and we found they keep athletes going longer than before. BCAAs in amounts that are easily absorbable with carbs, electrolytes, and water during long-term exercise worked in many, many field tests – real-life use. It’s complicated, as always, but with new research tools that cast a wide and sensitive net, the reason for adding BCAAs to long & strenuous cycling, running, triathlons, gravel races, wilderness races, etc. has become clear.

Simply put, BCAAs unlock a final emergency fuel source when all other options are exhausted.

As exercise goes past two hours and your glycogen stores are dwindling, your body mobilizes and cannibalizes BCAAs to feed muscle cell energy production. Glycogen is storage. It becomes priority fuel because you need more than the carbs you can take in, when fat and carb oxidation have been maxed out for hours, and their levels and mobilization are getting dicey. This is when a few grams of BCAAs act as triggers to make more energy from BCAAs and other aminos and from ubiquitous fatty acids.


Now that we’ve made the claim, here’s the proof.

As detailed in our EFS Research Packet section on BCAAs, there is good evidence that taking several grams of BCAAs and L-Glutamine each hour of multi-hour exercise has performance extensions benefits. Simply measuring blood BCAA levels before and after exercise leaves a blank insight during exercise,  but looking at BCAA levels during exercise consistently shows they are disappearing from blood. They’re clearly doing something your body wants to do or they would not be disappearing. So how do we look deeper into exercise physiology to find out what, exactly, that is? Metabolomics!

Metabolomics tracks chemical processes by measuring compounds in blood, urine, or sweat with NMR technology – Nuclear Magnetic Resonance. NMR can positively identify many different compounds at the same time in small amounts because of the unique electromagnetic signals each molecule emits. This tells you what processes are occurring by looking at the aftermath of those processes – we know what’s happened because every chemical process in the body leaves evidence – in this case, metabolites, which are evidence of BCAAs having been metabolized.

Metabolomic studies of marathon runners showed losses of BCAAs and suggestions of where those BCAAs were going (Stander 2018, 2020). Other recent studies confirm it. Here are the details.

Recent human studies used cycle ergometry regimens to deplete muscle glycogen. They then manipulated the diet for the next 24 hours to prevent glycogen repletion. After this period, the athletes completed another exercise bout in order to see what the body would do in the absence of glycogen stores. For the second exercise session, the athletes performed 80 minutes of cycle ergometry at ~64% VO2max while ingesting 146g of carbs (~100g/hour).

Serum metabolomics were measured at baseline, before exercise, and immediately after exercise. Of the 309 metabolite compounds that showed a change with time, 78% were related to amino acid or fatty acid metabolism. BCAA metabolites increased 64%, indicating that BCAAs were being actively converted into energy metabolites when athletes were low on glycogen stores, but not when glycogen was still available. 

In other words, you need BCAAs during strenuous, carb-burning, exhausting exercise, because they help maintain energy when exercise output outpaces intake and depletes glycogen stores. When there’s an energy deficit, BCAAs are not used for anabolism (building muscle); they’re used to stimulate energy production and become fuel for continuing exercise. If you do not ingest BCAAs during exercise, they have to come from your body – muscles and liver breakdown, which will eventually limit your total exercise performance. Keep in mind that this finding happened with maximal carb intake during cycling – just like using EFS or EFS-PRO.

Citations for BCAAs During Exhausting Long-Duration Exercise: Bester 2021; EFS Research Packet 2022; Gwin 2022; Margolis 2021, 2022; Stander 2018, 2020


We’ve known for decades that blood BCAA levels decrease during exercise. Metabolics tell us why: They’re being burned for fuel (and for activating fat-burning, keto-burning pathways) when carbs run out. A steady supply of BCAAs runs fuel through these pathways to keep them up-regulated, thus generating more energy for you to perform. Metabolomics have deepened our insight into what long-duration exercise needs, and the BCAAs in EFS and EFS-PRO are a critical addition – one that many hydration mixes and energy gels still overlook.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.


Bester R, Stander Z, Mason S, Keane KM, Howatson G, Clifford T, Stevenson EJ, Loots DT. Characterizing marathon-induced metabolic changes using 1H-NMR metabolites. Metabolites. 2021 Sep27;11(10):656.

Margolis LM, Karl JP, Wilson MM, Coleman JL, Whitney CC, Pasiakos SM. Serum branched-chain amino acid metabolites increase in males when aerobic exercise is initiated with low muscle glycogen. Metabolites. 2021 Nov30;11(12):828.

Margolis LM, Karl JP, Wilson MM, Coleman JL, Whitney CC, Pasiakos SM. Serum branched-chain amino acid metabolites increase when aerobic exercise is initiated with low muscle glycogen. Med Sci Sports Exerc. 2022 May;54(5S):S75. Abstract328.

Stander Z, Luies L, Mienie LJ, Keane KM, Howatson G, Clifford T, Stevenson EJ, Loots DT. The altered human serum metabolome induced by a marathon. Metabolomics. 2018 Nov3;14(11):150.

Stander Z, Luies L, Mienie LJ, Van Reenen M, Howatson G, Keane KM, Clifford T, Stevenson EJ, Loots DT. The unaided recovery of marathon-induced serum metabolome alterations. Sci Rep. 2020 Jul6;19(1):11060.
March 16, 2023 — Luke Bucci

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