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Debunking the BCAA Myth: A Dive into Muscle Growth, Fatigue, and Sleep

There's currently a buzz around the importance of optimal protein intake and incorporating resistance training for improved health and longevity. It's fantastic – I hope this trend never fades. It's undeniable how crucial it is to build and maintain muscle while ensuring an adequate protein intake in our diets.

Many individuals are keen on building muscle, and I've noticed a surge in the popularity of BCAA supplements lately. Perhaps it's due to algorithms or a growing interest in optimizing muscle growth during workouts. Regardless, I want to shed light on why I don't typically recommend BCAA supplementation in my practice as an integrative functional nutrition dietitian.

BCAAs, or branched-chain amino acids, consist of leucine, valine, and isoleucine.

The widely-believed claim is that supplementing with BCAAs can elicit an anabolic response by stimulating muscle protein synthesis. A quick Google search on BCAAs yields hundreds of articles making this assertion, often citing studies to support it.

Maximizing muscle protein synthesis (MPS) involves achieving a balance between muscle protein breakdown and muscle protein synthesis. It's essentially how muscle is built, as our bodies experience a constant turnover of protein from an amino acid reserve pool. An anabolic state occurs when the rate of muscle protein synthesis exceeds the rate of muscle protein breakdown, resulting in a gain of muscle mass. This state is thought to be driven by an increase in muscle protein synthesis, although theoretically, it could also result from a decrease in muscle protein breakdown.

The goal of BCAAs is to enhance this anabolic state.
  • However, it's crucial to note that in order to synthesize new muscle protein, all amino acids must be present in adequate amounts. Therefore, while BCAAs are valuable, they aren't inherently superior on their own. The rate of synthesis will always be limited by the availability of other essential amino acids (EAAs).

  • Most studies conducted on rats indicate a transient or acute spike in stimulation of MPS with BCAA supplementation. However, what's physiologically relevant is a sustained stimulation of MPS, as muscle is built over time, not within a mere two-hour window.

  • BCAAs acutely stimulate MPS by utilizing endogenous stores of other precursors of protein synthesis. However, this amino acid reserve pool is limited and depletes quickly. Consequently, you'll still need to ingest more of the other amino acids to support muscle growth effectively.

Attempting to create an anabolic state solely through BCAA supplementation poses a challenge. Your body would need to break down endogenous proteins to compensate for the missing amino acids, making it physiologically implausible.

Studies measuring intravenous infusion over extended periods, such as 3 and 16 hours, gauge the rates of disappearance of phenylalanine, considered a reflection of MPS as protein synthesis (PS) is the only fate of phenylalanine taken up by muscles from plasma. In these studies, phenylalanine levels exhibited no change, indicating that breakdown was also reduced, mirroring the decrease in MPS, thereby indicating a persisting catabolic state. Meanwhile, BCAA levels increased, but concentrations of other essential amino acids decreased. This decrease in availability of essential amino acids actually led to a decrease in MPS due to the lack of necessary building blocks, resulting in a net decrease in protein breakdown.

The other significant claim surrounding BCAAs is their purported ability to reduce muscle fatigue when consumed before a workout.

This is said to occur through competition with tryptophan for transporters to cross the blood-brain barrier (BBB) and enter the brain. In the brain, serotonin levels signal to the body that it's fatigued. Since tryptophan is a precursor to serotonin, the idea is that by reducing tryptophan levels in the brain, the fatigue signal is blocked, potentially allowing for more repetitions during a workout to build muscle.

However, I have reservations about this claim for two main reasons.

  • Firstly, the potential benefits of reducing tryptophan levels in the brain are outweighed by the numerous disease states and functional imbalances associated with decreased tryptophan levels.

  • Secondly, muscle growth is primarily driven by progressive challenge, and one often overlooked aspect of successful strength training is perceived effort.

The Rate of Perceived Effort is a skill learned through understanding your body's different levels of exertion and gauging the intensity of your work.

If you're overworking or underworking your muscles, you'll likely see minimal progress. Even in a workout class where everyone does the same number of reps, uses the same weights, and burns the same calories, each individual may have a different Rate of Perceived Exertion (RPE) and consequently, different results.

Constantly masking fatigue perception with quick-fix solutions won't lead to the desired results in muscle building.

Potential Link to Disrupted Sleep

Disruption of tryptophan metabolism is associated with various neurodegenerative diseases. The kynurenine pathway, a major regulator of the immune response, plays a crucial role here.

Adequate sleep is crucial for alleviating neuroinflammation and aiding in the cellular clearance of metabolic toxins produced within the brain. Sleep deprivation, on the other hand, triggers enzymatic degradation of tryptophan via the kynurenine pathway, leading to an accumulation of neurotoxic metabolites such as kynurenic acid in various brain regions. Higher levels of kynurenic acid can trigger apoptosis, contribute to cognitive decline, and inhibit neurogenesis.

This is why I refrain from recommending BCAA supplements for muscle growth and fatigue recovery.

Let's delve into the importance of sleep:

  • Sleep latency, or the time it takes to fall asleep once the lights are turned out, serves as a significant indicator of sleep cycle health. It reflects an individual's sleep efficiency and can signify whether they have good sleep quality.

  • If you struggle to fall asleep or experience disturbances throughout the night, it can result in sleep debt and lower sleep efficiency. The ideal sleep latency falls between 15-20 minutes. Falling asleep too quickly may indicate sleep deprivation, while prolonged latency can lead to insomnia.

  • Total sleep is divided into two stages: REM (rapid eye movement) and NREM (non-rapid eye movement). REM sleep involves dreaming, while NREM sleep promotes muscle relaxation and deep sleep. Healthy sleep latency is vital for cycling through all four stages of sleep appropriately.

  • Falling asleep quickly upon hitting the bed may suggest a buildup of sleep debt, reflecting poor sleep quality and sleep deprivation over time.

For a deeper dive into getting high quality sleep for your health check out my comprehensive guide to sleep blog post.

In conclusion, while the allure of BCAA supplements for muscle growth and fatigue recovery may be tempting, it's essential to consider the broader picture of holistic health and fitness. Perceived effort, an often-overlooked aspect of training, holds significant importance in achieving progress. Rather than relying solely on supplements, understanding and optimizing our body's responses to exercise can lead to more sustainable and effective results. Moreover, prioritizing factors such as adequate sleep, which plays a crucial role in muscle recovery and overall well-being, cannot be overstated. By embracing a comprehensive approach that encompasses nutrition, exercise, rest, and mindfulness, we can unlock our true potential for long-term health and fitness success. Remember, it's not just about what we consume but how we nourish our bodies and minds to thrive both in and out of the gym.


  1. Kim HK, Suzuki T, Saito K, Yoshida H, Kobayashi H, Kato H, Katayama M. Effects of exercise and amino acid supplementation on body composition and physical function in community-dwelling elderly Japanese sarcopenic women: a randomized controlled trial. J Am Geriatr Soc. 2012 Jan;60(1):16-23. doi: 10.1111/j.1532-5415.2011.03776.x. Epub 2011 Dec 5. Erratum in: J Am Geriatr Soc. 2012 Mar;60(3):605. PMID: 22142410.

  2. Jackman SR, Witard OC, Philp A, Wallis GA, Baar K, Tipton KD. Branched-Chain Amino Acid Ingestion Stimulates Muscle Myofibrillar Protein Synthesis following Resistance Exercise in Humans. Front Physiol. 2017 Jun 7;8:390. doi: 10.3389/fphys.2017.00390. PMID: 28638350; PMCID: PMC5461297.

  3. Fuchs CJ, Hermans WJH, Holwerda AM, Smeets JSJ, Senden JM, van Kranenburg J, Gijsen AP, Wodzig WKHW, Schierbeek H, Verdijk LB, van Loon LJC. Branched-chain amino acid and branched-chain ketoacid ingestion increases muscle protein synthesis rates in vivo in older adults: a double-blind, randomized trial. Am J Clin Nutr. 2019 Oct 1;110(4):862-872. doi: 10.1093/ajcn/nqz120. PMID: 31250889; PMCID: PMC6766442.

  4. Della Torre, S., Benedusi, V., Pepe, G. et al. Dietary essential amino acids restore liver metabolism in ovariectomized mice via hepatic estrogen receptor α. Nat Commun 12, 6883 (2021).

  5. Bhat A, Pires AS, Tan V, Babu Chidambaram S, Guillemin GJ. Effects of Sleep Deprivation on the Tryptophan Metabolism. International Journal of Tryptophan Research. 2020;13. doi:10.1177/1178646920970902

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