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Branched-chain amino acids
Leucine, isoleucine and valine form the group of branched-chain amino acids (BCAAs). As protein building blocks, they are natural components of foods containing protein such as meat, fish or legumes. In the context of a normal diet, BCAAs are always ingested in combination with other amino acids. BCAAs can be extracted from protein sources and can be consumed in isolated form, as single BCAA or as combination of all three BCAAs or only of two of them, for example in the form of certain food supplements.However, there are indications of possible health risks associated with higher intake levels of BCAAs in isolated form.
These particularly relate to undesirable changes in laboratory parameters, for example increased blood ammonia levels. The German Federal Institute for Risk Assessment (BfR) has taken this as a reason to derive guidance values for tolerable supplemental daily intakes of leucine, isoleucine and valine in isolated form, when ingested as a single BCAA or as combination of the BCAAs.
The available scientific human data are currently insufficient to derive these guidance values. Therefore, data obtained from toxicological animal studies with these amino acids were used. On the basis of the highest daily intake levels, where no toxic effects were observed (No Observed Adverse Effect Level or short NOAEL) identified in these studies, and taking into account uncertainty factors for the extrapolation of these toxicological parameters determined in animal studies to humans, the BfR has derived the following guidance values for adults.
They apply to the intake of isolated branched-chain amino acids (as single BCAA or combination of the BCAAs), which can be consumed daily in addition to the normal diet:
Leucine: 4.0 g per day
Isoleucine: 2.2 g per day
Valine: 2.0 g per day
BCAAs (total): 8.2 g per day (corresponding to the sum of the guidance values for the individual BCAAs)
The available findings also suggest that branched-chain amino acids should not be taken individually, but in combination of all three BCAAs. Due to insufficient data, it is currently not possible to derive guidance values for the tolerable supplemental daily intake of BCAAs in isolated form for children, adolescents, pregnant and breast-feeding women. The BfR therefore recommends that these population groups avoid relevant intakes of isolated branched-chain amino acids, for example from food supplements or sportsfoods. In addition, the derived guidance values do not apply to individuals with reduced kidney function and those who follow a diet with a low protein intake.These individuals should consult their physician before consuming relevant isolated amounts of these amino acids.
Expert opinion: Food supplements - High intake of isolated branched-chain amino acids can lead to health impairments 
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20/12/2019
