Liver disease. Severe liver disease often causes impaired brain function (encephalopathy) due to very high levels of tyrosine and tryptophan in the brain. Because BCAAs com-
pete with these amino acids for transport into the brain, supplemental BCAAs (taken orally or intravenously), in conjunction with vitamin B6, lower brain levels of tyrosine and tryptophan and may improve mentation.4 9
Anorexia. Appetite and food intake are increased when serotonin levels in the brain are low. By reducing brain uptake of tryptophan (the precursor of serotonin), BCAAs may increase appetite and food intake in disorders where appetite is lost (chronic infection, AIDS, cancer).
Neuromuscular disorders. Combined supplementation with valine, leucine, and isoleu-cine may be of benefit in amyotrophic lateral sclerosis (ALS).10 Huntington chorea is characterized by low levels of circulating BCAAs, and supplemental BCAAs may also be beneficial in this disorder.
High doses of BCAAs may reduce transport of tryptophan (the precursor to serotonin) into the brain. In conditions that may be aggravated if serotonin levels are lowered (insomnia, depression, migraine), caution should be exercised with high doses of BCAAs.
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