Branched-Chain Amino Acids - Nutrition

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What are Branched-Chain Amino Acids?

The branched-chain amino acids (i.e. leucine, isoleucine and valine) are essential dietary amino acids for dogs and cats. Leucine is ketogenic; valine is gluconeogenic; and isoleucine is both ketogenic and gluconeogenic. Dietary branched-chain amino acids are absorbed by a neutral amino acid transporter in the small intestine (particularly the jejunum) and plasma branched-chain amino acids are actively reabsorbed in the proximal tubule of the kidney.

Why are they Important?

Branched-chain amino acids are structural components of protein. The hydrophobic side chains of branched-chain amino acids induce inward folding of protein structures. Severe liver disease may result in decreased plasma branched-chain amino acid concentrations relative to aromatic amino acids, and this is thought to play a role in the clinical signs of hepatic encephalopathy[1][2]. However, the clinical impact of attempting to alter amino acid balance favouring branched-chain amino acids in animals with hepatic encephalopathy is unknown.

Roles in the Body

Isoleucine, leucine and valine are constituents of protein. Leucine is also a key catabolic regulator of l branched-chain amino acids[3]. Leucine also influences protein synthesis and muscle deposition by increasing plasma insulin secretion[4], sensitivity of insulin binding to muscle cells[5][6][7], and inhibiting muscle catabolism[8][9].

Consequences of Branched-Chain Amino Acid Deficiency


Puppies fed diets deficient in leucine, isoleucine or valine experienced decreased food intake and weight loss[10][11]. There are no published studies evaluating branched-chain amino acid deficiencies in adult dogs.


Kittens fed diets deficient in leucine or valine experienced decreased food intake and underwent weight loss[12]. Kittens fed diets deficient in isoleucine had not only poor growth, but porphyrin-like staining around the eyes, nose and mouth with ataxia and sloughing of paw pads[13]. There are no published studies evaluating branched-chain amino acid deficiencies in adult cats.


There are no published reports of acute or chronic toxicity of any branched-chain amino acid in dogs. In contrast, in cats there is evidence that feeding high doses of leucine can result in decreased plasma concentrations of other plasma amino acids and cause a depression of growth rate in kittens[14]. Leucine controls degradation of all branched-chain amino acids and prevents toxicity with high intake[3].

Dietary Sources

Sufficient leucine, isoleucine, and valine are found in plant and animal protein sources, such as muscle meat, eggs, dairy protein (i.e. casein), cereal grains, and pulses (i.e. legumes).

Diagnosing Branched-Chain Amino Acid Deficiency

Diagnosis of branched-chain amino acid deficiency is based on fasted plasma amino determination.


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  2. Meyer HP, et al. Effects of a branched-chain amino acid-enriched diet on chronic hepatic encephalopathy in dogs. Metab Br Dis 1999;14:103-110.
  3. 3.0 3.1 Harris RA, et al. Regulation of branched-chain α-keto acid dehydrogenase kinase expression in rat liver. J Nutr 2001;131:841S-845S.
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  10. Milner JA. Assessment of indispensable and dispensable amino acids for the immature dog. J Nutr 1979;109:1161-1167.
  11. Milner JA. Assessment of the essentiality of methionine, threonine, tryptophan, histidine and isoleucine in immature dogs. J Nutr 1979;109:1351-1357.
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