L-Isoleucine
One of the three branched-chain amino acids, sold alone for glucose uptake. Human evidence for isoleucine on its own is essentially absent; what exists is animal work and trials of the BCAA mixture.
Evidence last reviewed: August 2026
What the science says
- The glucose-uptake evidence is animal-level Limited evidence
The claim traces to animal work showing isoleucine increases muscle GLUT1 and GLUT4 and intestinal glucose transporter concentrations. No randomised human trial has tested isolated isoleucine for glycemic control.
- Benefits attributed to it come from BCAA mixtures Limited evidence
Meta-analyses showing reduced muscle soreness and damage markers used leucine-dominant BCAA blends, so isoleucine's individual contribution cannot be separated out.
Dosage & safety
Studied doseNo studied human dose exists. Products typically supply 1–3 g/day, usually inside a 2:1:1 BCAA ratio rather than alone.
SafetyAmino acids at these amounts are generally well tolerated. Isolated BCAA intake competes with other amino acids for transport; chronically elevated BCAA exposure is associated with insulin resistance in observational data. Contraindicated in maple syrup urine disease.
Scientific references
- Effects of isoleucine on glucose uptake through the enhancement of muscular membrane concentrations of GLUT1 and GLUT4 and intestinal membrane concentrations of Na+/glucose co-transporter 1 (SGLT-1) and GLUT2
- Attenuating Muscle Damage Biomarkers and Muscle Soreness After an Exercise-Induced Muscle Damage with Branched-Chain Amino Acid (BCAA) Supplementation: A Systematic Review and Meta-analysis with Meta-regression
Where to buy
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Related in Physical performance
- Creatine (monohydrate) Strong evidence
- Whey Protein Strong evidence
- Caffeine Strong evidence
- Beta-Alanine Moderate evidence
- BCAA (Branched-Chain Amino Acids) Limited evidence
- EAA (Essential Amino Acids) Moderate evidence