Branched Chain Amino Acids

Reviewed by: BD Editors

Definition

The branched-chain amino acids or BCAAs, leucine, isoleucine, and valine are three of the nine nutritionally essential amino acids. These three ingredients form a popular health supplement primarily consumed by sports enthusiasts as it is believed they contribute to muscle tissue synthesis; however, the true value of BCAA supplements has yet to be proved.

BCAA supplements: a muscle myth?
BCAA supplements: a muscle myth?

BCAA Benefits

BCAA benefits are completely dependent upon the availability of other amino acids within the human body. It has been suggested that the effects of BCAAs in terms of muscle mass are transient, as they compete with protein carrier molecules necessary to transport a variety of amino acids around the body. When transport proteins become saturated with high levels of branched chain amino acids, the body becomes deficient in the aromatic amino acids,    phenylalanine, tryptophan, tyrosine, and histidine. As aromatic amino acids are also precursors to thyroxine, 5-hydroxytryptophan, and L-DOPA, overuse of BCAA supplements are likely to cause metabolic system and neurotransmitter imbalance.

Cell membrane transporter proteins
Cell membrane transporter proteins

BCAA Benefits in Protein Synthesis

BCAA benefits in protein synthesis studies are often limited to testing on rodents where higher levels of BCAAs stimulate protein synthesis and inhibit protein catabolism. In humans, this role seems to be less to do with protein synthesis and more to do with the inhibition of protein catabolism or protein degradation.

An anabolic effect refers to the synthesis of complex molecules from smaller ones, such as the synthesis of protein-based muscle tissue from singular amino acids. A catabolic effect describes the breakdown of a complex molecule into its individual parts. Branched chain amino acids seem to slow down catabolism. This means that, although the rate of muscle mass production is not increased through BCAA supplementation in humans, a slower degradation curve can lead to higher levels of muscle tissue in the right circumstances. One should certainly not ignore the fact that cell longevity in the case of muscles may not be a positive change; the younger the cell the better it performs.

Increased muscle mass does not depend on a small selection of amino acids but a wide range of nutritionally essential and nonessential ones. When the availability of one amino acid is compromised, this can affect the entire anabolic process. By supplementing a small group, one is still limited to the availability of a complete range of amino acids, enzymes, and transport proteins. Because of this, the positive effects of BCAAs on muscle mass are often transient and, over time, other ingredients for muscle synthesis diminish or are outcompeted. In addition, the availability of amino acids in skeletal muscle synthesis depends upon muscle breakdown. During and immediately after a meal, amino acids are transported via the blood to muscle sites where they contribute to muscle synthesis. Once a person has ceased eating, this availability rapidly diminishes; it is then up to the catabolic breakdown of older muscle cells to provide further amino acids for the anabolic building up. As BCAAs slow down degradation and so lower the available levels of free amino acids, it is possible that, in the long run, these supplements actually have a negative effect on muscle production.

When a decision has been made to take BCAA supplements to increase muscle mass one should carefully time ingestion to immediately preceding a high-energy workout and in combination with other essential and nonessential amino acids. In this way, competing amino acids have the same opportunity to bond with transport proteins and use can be made of immediately available sources in the blood plasma. When this pre-training timescale is respected, energy levels, muscle mass and levels of muscle damage seem to be positively affected.

Do BCAAs really increase muscle mass?
Do BCAAs really increase muscle mass?

BCAA Benefits in the Brain

BCAA benefits in the brain coincide with the competition for the transport proteins of aromatic amino acids and their implications in neurotransmitter synthesis and are currently being researched as a means to treat manic episodes. Branched chain amino acids are nitrogen donors which means they can help to provide a positive nitrogen balance in the brain by contributing to excitatory glutamate and inhibitory gamma-aminobutyric acid (GABA) synthesis.

As BCAAs are able to cross the blood-brain barrier, higher levels prevent the aromatic amino acids tryptophan, tyrosine, and phenylalanine from entering the brain. Tryptophan is a precursor of serotonin and tyrosine and phenylalanine are catecholamine precursors; the action of supplementary branched chain amino acids, therefore, directly affects the synthesis and release of serotonin and catecholamines such as dopamine, norepinephrine, and epinephrine. Yet, as in the case of the majority of central nervous system physiology, the full role of BCAAs in excitatory and inhibitory neurotransmitter synthesis remains unclear. Rodents given excess BCAA had low levels of serotonin in the brain that caused the animals to overeat and become obese, while health forums often include queries from BCAA supplement consumers asking whether their experiences of low mood or mood swings may be associated with their ingestion.

BCAAs affect dopamine and serotonin
BCAAs affect dopamine and serotonin

BCAAs and Adipose Tissue

Unlike other nutritionally essential amino acids, the liver does not produce sufficient enzymes for the catabolism of leucine, isoleucine, and valine. In the liver, the first enzyme -mitochondrial branched chain aminotransferase (BCAT2) – is responsible for BCAA catabolism in peripheral tissue.  Although research is as yet in the dark regarding the physiology behind BCAA benefits, it is believed that they signal the presence of nutrients to the body and brain, help to regulate protein synthesis and protein breakdown, play a role in insulin secretion, and may even contribute to the central nervous system’s control mechanisms for food intake and energy balance.

It is generally accepted that muscle tissue is the major site of BCAA catabolism, but more recent studies implicate fat tissue or adipose tissue in the down-regulation of BCAA catabolism; it may be that adipose tissue stops the body from making use of available BCAAs. For example, research into BCAA levels in those suffering from obesity, insulin resistance, and metabolic syndrome has found a link between the presence of large amounts of fat tissue and high circulating but non-catabolized branched chain amino acids. After gastric bypass surgery, these circulating levels decrease, as does insulin resistance and appetite. The latter may be the result of a return to normal BCAA function where these amino acids are once again able to act as nutrient signaling compounds.

Excess BCAAs - insulin resistance
Excess BCAAs: insulin resistance

Correct Use of BCAA Supplements

The correct use of BCAA supplements is important in order to gain maximum benefit with minimum damage. These are certainly not the muscle-building miracle they are advertised to be but a nutritional supplement which is not yet fully understood. What is more, BCAAs are linked to tumor growth as they provide an energy source for cancer cells. Supplementation should, therefore, be very carefully considered.

A healthy, varied diet provides the body with every essential nutrient so amino acid supplementation should be avoided, especially by those who do not partake in regular high-level physical activity. To minimize the effect of fat tissue upon BCAA performance, sources of amino acids should come primarily from fish and plant-based protein. These foods provide sufficient and balanced quantities of nutrients in the daily diet. High-fat diets in combination with BCAA supplements may cause serious detrimental effects upon one’s health. One study in mice resulted in significantly high mortality rates in rodents fed high-fat diets with supplementary BCAAs when compared to those without supplementation. Even more importantly, none of those on high-fat and low BCAA diets died.

Plant-based proteins for BCAAs
Plant-based proteins for BCAAs

BCAA supplementation, when considered of use by an individual, should only be taken immediately preceding high-level physical activity so that available levels are directly available from blood plasma and can temporarily help to make improvements during high-energy exercise physiology. In addition, BCAAs should be part of a mixed essential and non-essential amino acid product to avoid competition and provide a full package of ingredients. Finally, BCAA supplements should not be considered as a long-term therapy as these effects have not been sufficiently studied and may be harmful. Branched chain amino acid supplements should only be seen as a short-term and transient nutritional supplement.

BCAA research is still ongoing
BCAA research is still ongoing

Cite This Article

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Biologydictionary.net Editors. “Branched Chain Amino Acids.” Biology Dictionary, Biologydictionary.net, 08 Jan. 2020, https://biologydictionary.net/branched-chain-amino-acids/.
Biologydictionary.net Editors. (2020, January 08). Branched Chain Amino Acids. Retrieved from https://biologydictionary.net/branched-chain-amino-acids/
Biologydictionary.net Editors. “Branched Chain Amino Acids.” Biology Dictionary. Biologydictionary.net, January 08, 2020. https://biologydictionary.net/branched-chain-amino-acids/.

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