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Isoleucine

Isoleucine is one of three branched-chain amino acids (BCAAs) along with leucine and valine. It is an essential amino acid required for muscle protein synthesis. NO GRADED OUTCOMES for isolated isoleucine supplementation - typically studied as part of BCAA or protein supplements. Unlike leucine (which directly stimulates mTOR/muscle synthesis), isoleucine's unique role may be glucose uptake enhancement. RDA is 19 mg/kg/day, easily met through dietary protein. No strong evidence supports isolated isoleucine supplementation over complete proteins or BCAAs. Best consumed as part of complete protein sources rather than alone.

Quick Answer

What it is

Isoleucine is one of three branched-chain amino acids (BCAAs) along with leucine and valine. It is an essential amino acid required for muscle protein synthesis.

Key findings

  • Grade C: Blood Glucose (Acute Reduction)
  • Grade D: Innate Immune Function (Beta-Defensin Induction)
  • Grade D: Muscle Protein Synthesis

Safety

No specific caution or interaction language was detected in the current summary/outcome notes.

ℹ️ Quick Facts: Isoleucine

Quick Facts: Isoleucine

  • Best Evidence:Grade D
  • Conditions Studied:1
  • Research Outcomes:4
  • Key Effect:Acute Gastroenteritis
Outcomes by grade:
A0
B0
C1
D3
1 conditions · 4 outcomes

Detailed Outcomes

C
Blood Glucose (Acute Reduction)
In multiple rodent studies, acute isoleucine administration reduced plasma glucose by ~20% via increased skeletal muscle glucose uptake (up to 73% above controls), enhanced glucose oxidation, and suppressed hepatic gluconeogenesis through a PI3K-dependent, insulin-independent mechanism (Doi et al. 2003, 2005, 2007). A porcine study confirmed upregulation of GLUT1 and GLUT4 transporters (Zhang et al. 2016). However, chronic supplementation impaired glucose tolerance in lean mice (O'Rielly et al. 2020), and no human trials have validated these acute effects.
moderate↓Improves
D
Innate Immune Function (Beta-Defensin Induction)
L-isoleucine stereospecifically induces beta-defensin expression in epithelial cells via NF-kB signaling (Fehlbaum et al. 2000). In mice with active tuberculosis, intratracheal isoleucine upregulated beta-defensins 3 and 4, reducing bacterial loads in both drug-sensitive and MDR strains (Rivas-Santiago et al. 2011). A small pediatric RCT (n=50) of isoleucine-supplemented ORS showed non-significant increases in beta-defensin levels (Alam et al. 2011).
small↑Improves
D
Muscle Protein Synthesis
Isoleucine independently activates mTOR and S6K1 phosphorylation in bovine mammary cell culture (Appuhamy et al. 2012), but BCAAs alone are insufficient to stimulate net muscle protein synthesis in humans due to the requirement for all essential amino acids (Wolfe 2017 review). High-dose isoleucine may compete with leucine for shared intestinal and muscle transporters, potentially blunting leucine's anabolic effect (Santos & Nascimento 2019).
small↑Improves
D
Diarrhea Severity (Pediatric Acute)
A single double-blind RCT in 50 children (aged 6-36 months) with acute watery diarrhea found that L-isoleucine (2 g/L) added to oral rehydration salts significantly reduced stool output on day 3 (p=0.035) and ORS intake on day 1 (p=0.04), though cumulative stool reduction (26%) and diarrhea duration did not reach statistical significance (Alam et al. 2011).
small↓Improves

Evidence by Condition

Best grade per condition (each condition may have multiple outcomes)

DAcute Gastroenteritis
1
↓Diarrhea Severity (Pediatric Acute)Improves

Research Citations (13)

Dietary isoleucine restriction decreases body weight and extends lifespan in mice
(2023)
PMID: 37939658
The adverse metabolic effects of branched-chain amino acids are mediated by isoleucine and valine
(2021)
PMID: 33887198
Isoleucine supplementation does not improve glucose tolerance or metabolic health in obese mice
(2020)
PMID: 32823899
New concepts of leucine supplementation and skeletal muscle protein synthesis: a review
(2019)
PMID: 31508659
Isoleucine plays an important role in the growth, immune function, protein metabolism, fatty acid metabolism, and glucose transport of animals
(2019)
PMID: 30843485
Isoleucine enhances glucose uptake through the upregulation of GLUT1 and GLUT4 and the increase of Na+/glucose co-transporter 1 in muscle cells and hepatic cells
(2016)
PMID: 27464458
Isoleucine and leucine independently regulate mTOR signaling and protein synthesis in MAC-T cells and bovine mammary tissue slices
(2012)
PMID: 22298573
Isoleucine as adjunct therapy in active pulmonary tuberculosis through induction of antimicrobial peptides in murine models
(2011)
PMID: 21235540
Effect of L-isoleucine-supplemented oral rehydration solution on stool output and duration of diarrhea in children with acute watery diarrhea
(2011)
PMID: 21766553
Hypoglycemic effect of isoleucine involves increased muscle glucose uptake and whole body glucose oxidation and decreased hepatic gluconeogenesis
(2007)
PMID: 17299083

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