Glutamine vs BCAA: What's the Difference

Glutamine and BCAA are often sold in the same category of “amino acids for recovery,” and some manufacturers even mix them into a single product. In reality these are substances with different status, different functions and a different evidence base. Interestingly, in muscle tissue they are linked metabolically: one partly becomes a source of nitrogen for the other. The editorial team explains how this works and what follows from it.

Status: essential versus conditionally essential

BCAA - leucine, isoleucine and valine - belong to the essential amino acids. The body cannot synthesize their carbon skeleton, so they must come from food. Their main “sporting” reputation is linked to leucine, which activates the mTORC1 signaling pathway and triggers muscle protein synthesis.

Glutamine is formally a non-essential amino acid: a healthy person synthesizes it in large quantities, mainly in skeletal muscle, and also in the lungs, liver and adipose tissue. However, in a state of severe stress - burns, sepsis, major surgery - the requirement can exceed synthesis, so glutamine is classified as a conditionally essential amino acid.

This difference is fundamental. A deficiency of essential amino acids inevitably arises with inadequate nutrition, whereas a deficiency of glutamine in a healthy person who eats normally is unlikely. That is precisely why data obtained in intensive-care patients cannot be directly transferred to athletes.

Glutamine is the most abundant free amino acid in blood plasma and in muscle tissue. Its intramuscular pool is very large compared with the amount that can be obtained from a supplement, and this is another reason why it is hard to expect a noticeable effect on muscle from taking a few grams of glutamine.

Functions of glutamine in the body

Glutamine is the main carrier of nitrogen between tissues. It has two nitrogen atoms and allows ammonia to be safely transported from peripheral tissues to the liver and kidneys without raising the toxic level of free ammonia in the blood.

The second important function is nourishing rapidly dividing cells. Enterocytes of the small intestine and cells of the immune system, in particular lymphocytes and macrophages, actively use glutamine as a source of energy and nitrogen for the synthesis of nucleotides. From this arose the hypothesis that a drop in glutamine levels after exhausting exertion may weaken immunity.

The third function is participation in the regulation of acid-base balance. In the kidneys, ammonia is formed from glutamine, which binds hydrogen ions and is excreted in urine. In acidosis this process intensifies, and the kidneys' consumption of glutamine increases.

In addition, glutamine is a precursor of glutamate, glutathione (one of the main intracellular antioxidants) and other compounds. However, the presence of these functions does not mean that additional glutamine intake automatically enhances them: in a healthy person its own synthesis is usually sufficient.

The metabolic link between BCAA and glutamine

There is a direct metabolic link between BCAA and glutamine. Unlike most amino acids, which are broken down mainly in the liver, BCAA are largely metabolized in skeletal muscle. The first step is transamination by the BCAT enzyme, during which the amino group of BCAA is transferred to alpha-ketoglutarate to form glutamate.

Next, glutamate, with the participation of glutamine synthetase, adds another ammonia molecule and is converted into glutamine. An alternative pathway is the formation of alanine, which goes to the liver for gluconeogenesis. So part of the nitrogen from broken-down BCAA literally “flows” into glutamine and alanine, which leave the muscle into the blood.

This link is sometimes used in marketing: “BCAA maintain glutamine levels.” Theoretically yes, but in a healthy person with normal protein nutrition this process is happening constantly anyway, and additional BCAA are unlikely to change the picture substantially.

Practical conclusion: glutamine and BCAA are not competitors but participants in the same metabolic cycle. However, this does not make their combination in a single supplement justified: complete dietary protein supplies both BCAA and glutamine (and glutamate) in natural amounts.

The evidence base in sport

For BCAA the main hypothesis is stimulation of muscle protein synthesis. A study by Jackman et al. (2017) showed an acute increase in myofibrillar synthesis after BCAA intake, but its magnitude was noticeably smaller than after complete protein. Wolfe's review (2017) explains this by the lack of the remaining essential amino acids.

For glutamine the hypothesis is different - support of immunity and recovery. The work of Castell and Newsholme (1997) reported a lower incidence of self-reported infections after a marathon in the group that received glutamine. However, a review by Gleeson (2008) concluded that there is no convincing evidence of an effect of glutamine on immune function or performance in athletes, although a reduced plasma glutamine level after prolonged exertion is well documented.

As for muscle mass, glutamine has even weaker positions. In a controlled study by Candow et al. (2001), young people received high doses of glutamine or placebo over six weeks of resistance training, and no difference in muscle mass and strength between the groups was found.

So at the level of evidence, BCAA have at least an acute metabolic effect on protein synthesis, while glutamine has only isolated data on self-reported infections. Neither supplement has convincing evidence of improving long-term athletic performance in people with sufficient protein intake.

Safety and special groups

Both supplements in dietary doses are considered relatively safe for healthy adults. A risk assessment by Shao and Hathcock (2008) set an observed safe level (OSL) for glutamine of 14 g per day for supplemental intake, noting that higher doses in studies were also often well tolerated, but data for long-term intake are limited.

At the same time, clinical experience shows that “more” does not mean “better.” In the large randomized REDOXS trial (Heyland et al., 2013), high doses of glutamine in critically ill patients with multiple organ failure were associated with increased mortality. This concerns a specific population, but it well illustrates that glutamine is not a neutral substance under all conditions.

• Liver and kidney disease:any amino acid supplements only with a doctor's approval.
• Congenital disorders of BCAA metabolism:BCAA supplements are contraindicated.
• Pregnancy and breastfeeding:safety data are limited; intake should be discussed with a doctor.
• Oncological diseases:because of the role of glutamine in the metabolism of tumor cells, self-directed intake is inappropriate.

The IOC consensus statement on dietary supplements (Maughan et al., 2018) does not classify either glutamine or BCAA among supplements with a reliably proven effect on athletic performance and recalls the risk of product contamination, relevant for athletes undergoing doping control.

Editorial conclusions

Glutamine and BCAA are amino acids that differ in status and functions. BCAA are essential and are linked primarily to the signal that triggers muscle protein synthesis; glutamine is conditionally essential and is responsible for nitrogen transport, nourishing intestinal and immune-system cells, and acid-base balance.

In muscle they are metabolically linked: nitrogen from BCAA partly becomes nitrogen of glutamine. However, this biochemistry does not turn either supplement into an effective means for muscle growth in people who get enough protein.

The evidence base for both in sport is limited, and for glutamine on the question of muscle mass it is practically negative.

The editorial team broke down practical selection scenarios in the article “Glutamine vs BCAA: what to choose and for whom.” We also recommend the materials “BCAA vs leucine: what's the difference” and “EAA vs whey protein: what's the difference.”

References

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2. Candow DG, Chilibeck PD, Burke DG, Davison KS, Smith-Palmer T. Effect of glutamine supplementation combined with resistance training in young adults. Eur J Appl Physiol. 2001;86(2):142–149.
3. Castell LM, Newsholme EA. The effects of oral glutamine supplementation on athletes after prolonged, exhaustive exercise. Nutrition. 1997;13(7–8):738–742.
4. Wolfe RR. Branched-chain amino acids and muscle protein synthesis in humans: myth or reality? J Int Soc Sports Nutr. 2017;14:30.
5. Jackman SR, Witard OC, Philp A, et al. Branched-chain amino acid ingestion stimulates muscle myofibrillar protein synthesis following resistance exercise in humans. Front Physiol. 2017;8:390.
6. Shao A, Hathcock JN. Risk assessment for the amino acids taurine, L-glutamine and L-arginine. Regul Toxicol Pharmacol. 2008;50(3):376–399.
7. Heyland D, Muscedere J, Wischmeyer PE, et al. A randomized trial of glutamine and antioxidants in critically ill patients. N Engl J Med. 2013;368(16):1489–1497.
8. Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455.