| Dietary Sources | |
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L-leucine, L-valine and L-isoleucine are branched-chain amino acids (BCAA) and essential for humans. Humans are dependent on an exogenous supply.
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| Physiological effect | |
| Carbohydrate metabolism |
Stimulation of gluconeogenesis |
| Ammonia detoxification |
Neuroprotection through inhibition of aromatic amino acids uptake via the blood-brain barrier |
| Muscular system |
Protein synthesis and muscle building |
| Reference value according to food labelling regulations | |||
| (=100 % TB marking on label) | N/A | ||
| Requirements | |||
| L-isoleucine: | Adults: 10 mg/kg BW Children: 111 mg/kg BW |
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| L-Leucine: | Adults: 13 mg/kg BW Children: 153 mg/kg BW |
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| L-valine: | Adults: 14 mg/kg BW Children: 95 mg/kg BW |
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| Increased demand | Premature babies, stress, competitive sports, liver dysfunction (cirrhosis, hepatic encephalopathy), phenylketonuria, weight-loss diets, malnutrition | ||
| Nutrient safety | |||
| UL |
Long-term daily intake, at which no negative effects on health are to be expected |
L-leucine
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| NOAEL |
Maximum intake, with no observed adverse effect | ||
| Branched Chain Amino Acids: Structure and physiological task |
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Branched Chain Amino Acids (BCAA) belong to the essential amino acids and differ from the other amino acids by a nonpolar hydrocarbon side chain in the primary structure. It refers particularly to the amino acids L-leucine, L-valine and L-isoleucine. Protein metabolism is based on a constant build-up, breakdown and modification of the amino acid pool present in the body. For example, approximately 75 g of skeletal muscle protein is built up and broken down daily, of which 10% is exchanged in the form of free amino acids between the skeletal muscle and the amino acid pool in the plasma.1 While the enzyme systems for the degradation of the essential amino acids are mainly located in the liver cells, the BCAAs are mainly used by muscles and the brain.2 This is why branched-chain amino acids are indispensable for the build-up and maintenance of muscle mass and represent an additional source of energy under stress. Since BCAAs are not predominantly metabolized in liver tissue, they are also an important dietary component for maintaining protein balance in liver diseases, especially cirrhosis. |
| BCAA metabolism under heavy stress |
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In the case of long-term stress, branched-chain amino acids are the preferred source of energy in the musculature. In catabolic states, BCAAs are increasingly oxidized to glucose in the mitochondria of the skeletal muscles as part of gluconeogenesis and fed into the citrate cycle for energy production or used to ensure sufficient blood sugar levels.3 During intensive physical exertion, the concentration of leucine, isoleucine and valine decreases significantly due to the increased breakdown both in the plasma and in the musculature. This is more evident in untrained persons than in trained athletes.4 The decreasing concentration of BCCAs seems to be directly related to stress-induced muscle damage.5 Studies show that BCAA supplementation can reduce muscle damage6 and thus shorten recovery time. In addition, the weakened immune system is supported because BCAAs modify the cytokine pattern during exercise and can positively influence the TH1 lymphocyte response.7 |
| Promotion of anabolic processes in the regeneration phase and in sarcopenia |
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Regardless of their function as protein building blocks and in gluconeogenesis, BCAAs have additional anabolic influences on protein metabolism in muscle tissue. After long periods of stress, they can accelerate protein synthesis in muscle and slow down degradation rates by activating key enzymes for protein synthesis (mTOR and p70-S6 kinase).8 This is also related to the observed acceleration of regeneration using BCAA supplements. In older people, BCAAs can cause anabolic stimulation and counteract age-related muscle loss.9 In recovery, an increased intake of BCAAs also seems to have a positive effect on cognitive rehabilitation.10 In addition, a positive influence by supplementation with BCAA on depressive symptoms in patients with type 2 diabetes was also found.11 |
| Dietetic support for liver damage and liver cirrhosis |
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Since BCAAs are metabolized predominantly in the skeletal muscles and only to a small extent in the liver, they represent a lower load protein source than other amino acids in liver disease. In fact, long-term supplementation with BCAA reduces the risk of morbidity and mortality in liver cirrhosis patients.12 In another study it was documented that additional intake of BCAAs can positively influence both nitrogen balance and energy metabolism.13 In liver disease, the concentration of branched-chain amino acids in plasma is reduced and therefore the percentage of aromatic amino acids increased. Since both amino acid groups compete for the same transport system during uptake into the CNS, this leads to an increased uptake of the aromatic amino acids and an overall unfavorable influence on neurotransmitter activity. Hepatic encephalopathy manifests itself in poor concentration, memory and sleep disorders as well as cerebral dysfunction. Substitution with BCAA can increase hepatic and extrahepatic ammonia detoxification and normalize amino acid imbalances, thereby improving psychomotor function in liver disease.14 |
| Support of anabolic and immunological processes through individual amino acids |
| During physical exertion, whether through sport or an infection, amino acids are increasingly removed from muscle tissue to ensure protein biosynthesis in the immune system.15 Arginine, glutamine and cysteine seem to play an important role in maintaining immune competence.16 Targeted supplementation of malnourished individuals and during states of infection can improve immunological status through various mechanisms such as activation of T and B lymphocytes and macrophages and improvement of antibody and cytokine production.17 |
| Impact on | Symptoms |
| General well-being | Muscle weakness |
| Protein Synthesis | Muscle degradation, poor regeneration after exercise |
| Metabolism | Negative nitrogen balance (protein degradation), inadequate ammonia detoxification |
| Nervous system | Cerebral dysfunction |
| Effect | Indication | Dosage |
| Physiological effects at a low intake |
High performance sports | 4 – 10 g/d before and after training |
| To improve energy supply in striated muscle tissue | 2 - 5 g/d | |
| To maintain muscle protein status during intense exercise | 4 - 10 g/d | |
| Supplemental dietary measures for liver diseases | 15 - 20 g/d (0.3 g BCAA/kg BW) |
| General mode of administration | |
| When |
Branched-chain amino acids should be taken with meals. |
Notes:
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| Side effects | |
| No side effects are known to date. | |
| Contraindications | |
| Kidney insufficiency, maple syrup disease (impaired breakdown of BCAAs) | |
| Drug interactions | |
| None | No interactions known to date |
| Nutrient interactions | |
| L-tryptophan, tyrosine, phenylalanine, valine, leucine and isoleucine hinder transport through the blood-brain barrier | |
| Description |
| Branched chain proteinogenic amino acids |
| Related substances |
| L-Isoleucine is the natural form. The D and DL forms are insignificant isomers. L-valine is the natural form. DL-Valin is used industrially as a raw material for the production of certain drugs. L-Leucine is the natural form. |
| References |
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1 Biesalski, H. K., Grimm, P. Taschenatlas Ernährung, 3. Auflage. Stuttgart: Georg Thieme Verlag KG, 2004. References Interactions |
