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L-Isoleucine

Essential branched-chain amino acid crucial for muscle energy, endurance, and recovery support

Scientific nameL-Isoleucine FormulaC6H13NO2 Molecular weight131.17 g/mol CAS73-32-5
95 absorption score
9 safety / 10
20 USD per month
5 documented interactions

Check it against something

Evidence level A

L-Isoleucine with:

Compatibility score 82 out of 100
82 out of 100
Works better together Compatible. Timing differs, so follow each supplement's own window.

Check it against your whole stack →

What it does

mechanism and evidence for each claim

Enhanced muscle energy production

Provides direct fuel for muscle tissue during exercise

Metabolized directly in muscle for immediate energy Evidence A-grade 30 minutes to 2 hours during exercise

Improved exercise endurance

Delays muscle fatigue and extends exercise capacity

Preserves muscle glycogen and provides alternative fuel Evidence A-grade 1-4 weeks of consistent use

Enhanced muscle recovery

Supports muscle repair and reduces exercise-induced damage

Provides amino acids for protein synthesis and repair Evidence A-grade 2-6 hours post-exercise

Blood sugar regulation

Helps regulate glucose uptake and utilization

Enhances glucose transport into muscle cells Evidence B-grade 30 minutes to 2 hours

Wound healing support

Important for tissue repair and healing processes

Provides essential amino acids for protein synthesis Evidence B-grade 1-4 weeks

Others take these for the same thing

Same goal, different mechanism — check any of them against this one

Creatine Monohydrate Strength & power enhancement 3-5g A 95% Calcium Bone health & muscle function 1,000-1,200 mg A 30% Ashwagandha Stress management & energy 300-600mg A 75% Magnesium Glycinate Superior absorption sleep & muscle support 200-600 mg A 90% Vitamin B12 (Cyanocobalamin) Energy & nerve support 250-1000 mcg A 70% Coenzyme Q10 (CoQ10) Heart health & cellular energy 100-200mg A 10%

Every pair we checked

12 combinations scored by the engine
L-Isoleucine + L-Tryptophan High isoleucine may reduce tryptophan uptake into brain Needs attention 58
L-Isoleucine + Caffeine No documented interaction either way No known interaction 70
L-Isoleucine + Creatine Monohydrate No documented interaction either way No known interaction 70
L-Isoleucine + Vitamin D3 No documented interaction either way No known interaction 70
L-Isoleucine + Calcium Carbonate No documented interaction either way No known interaction 70
L-Isoleucine + Lactase No documented interaction either way No known interaction 70
L-Isoleucine + Bovine Collagen No documented interaction either way No known interaction 70
L-Isoleucine + DHA No documented interaction either way No known interaction 70
L-Isoleucine + Turmeric No documented interaction either way No known interaction 70
L-Isoleucine + Fish Oil (EPA/DHA) No documented interaction either way No known interaction 70
L-Isoleucine + Magnesium Oxide No documented interaction either way No known interaction 70
L-Isoleucine + Whey Protein Complete amino acid profile enhances isoleucine effects Works better together 82

Dosage

Pre during exercise
Daily1-6g
Maintenance1-2g daily
Athletic performance2-6g daily
Pre exercise1-3g before training
Post exercise1-3g after training

Before you take it

VeganYes

When to expect it

First Effects30-60 minutes for energy and endurance support
Peak Benefits2-4 weeks for muscle recovery and performance
Deficiency DevelopmentDays to weeks with inadequate protein intake
Toxicity OnsetVery rare, mainly digestive upset

How to measure it

$80-150
MarkerPlasma isoleucine levels
Optimal60-120 μmol/L
Deficient below<40 μmol/L
FrequencyOnly if monitoring protein status or research purposes

What actually reaches you

The label counts the carrier, your body does not
Absorption Very high 95 of 100 · best absorbed form of this compound
Delivered daily 3325 mg
Cost per 100 mg delivered $0.02 comparative — uses the absorption score, not a measured percentage

Works better with

3 documented
+
Leucine Valine

Other BCAAs work together for optimal muscle effects

Balanced BCAA profile prevents competition and imbalance · level A
+
Whey Protein

Complete amino acid profile enhances isoleucine effects

Provides all essential amino acids for protein synthesis · level A
+
Carbohydrates

Enhance isoleucine uptake and energy utilization

Insulin response improves amino acid uptake · level A

What not to take with L-Isoleucine

2 documented
!
Tryptophan

High isoleucine may reduce tryptophan uptake into brain

Competition for large amino acid transporter · mild significance
!
Other Large Amino Acids

High isoleucine may compete with phenylalanine, tyrosine

Shared transport mechanisms · mild significance

Medication interactions

Discuss these with a pharmacist before combining
diabetes-medications Minor

May enhance glucose lowering effects

What to do: Monitor blood glucose

diazoxide Minor

Isoleucine may counteract diazoxide effects

What to do: Monitor for drug effectiveness

Available forms

bioavailability compared
L-Isoleucine (Free Form) 95

L-Isoleucine (Free Form): Direct muscle energy, Fast absorption, Well-researched, Highly effective

Food sources

before you supplement
Whey protein 1.4-1.8g per 25g protein · 95
Lean meats (chicken, beef) 1.2-1.5g per 100g · 90
Fish (tuna, salmon) 1.1-1.4g per 100g · 90
Eggs 0.7g per 100g · 95

Too little

deficiency signs
  • Muscle weakness and fatigue
  • Poor exercise endurance
  • Slow muscle recovery
  • Impaired wound healing
  • Reduced immune function
  • Growth retardation in children

Too much

toxicity signs
  • Very rare with oral supplementation:
  • Digestive upset and nausea
  • Amino acid imbalance
  • Potential hypoglycemia
  • Generally excellent safety profile

Who benefits most

endurance-athletes

Essential for sustained muscle energy and fatigue resistance

1-3g before/during exercise
athletes-muscle-building

Important for muscle protein synthesis and recovery

1-3g post-workout
aging-muscle-preservation

Helps maintain muscle mass and energy with aging

1-3g with meals
weight-loss-muscle-sparing

Preserves muscle mass during caloric restriction

1-3g between meals
recovery-from-illness

Supports muscle protein synthesis during recovery

1-3g with meals

Where to buy it

compare forms first

Look for L-Isoleucine at 1-6g per serving. The form that matters here is L-Isoleucine (Free Form).

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What else affects it

Beyond other supplements
+
Carbohydrates

Enhance isoleucine uptake and energy utilization

Insulin response improves amino acid uptake

How it works

  • Metabolized directly in skeletal muscle for immediate energy
  • Stimulates glucose uptake into muscle cells
  • Supports muscle protein synthesis and repair
  • Helps maintain nitrogen balance during exercise
  • Important for hemoglobin and red blood cell formation
  • Regulates blood sugar and energy metabolism

Key findings

what the evidence supports
  • Essential for muscle energy metabolism (extensive research)
  • Effective for exercise endurance and fatigue resistance
  • Important for muscle recovery and protein synthesis
  • Critical for blood sugar regulation and glucose uptake

Sources: NIH Examine.com · data reviewed 2026-08-01

Compiled by Denis, who maintains this database and holds no medical qualification — every figure here is sourced or derived, never asserted. How we calculate it →

Common questions

What are the benefits of L-Isoleucine?

Documented effects: Enhanced muscle energy production; Improved exercise endurance; Enhanced muscle recovery; Blood sugar regulation. Provides direct fuel for muscle tissue during exercise

How much L-Isoleucine should you take per day?

The common daily range is 1-6g. By goal — maintenance: 1-2g daily; athletic performance: 2-6g daily; pre exercise: 1-3g before training; post exercise: 1-3g after training.

When is the best time to take L-Isoleucine?

Pre during exercise. First effects are typically reported within 30-60 minutes for energy and endurance support.

What are the side effects of L-Isoleucine?

At excessive doses: Very rare with oral supplementation:, Digestive upset and nausea, Amino acid imbalance, Potential hypoglycemia, Generally excellent safety profile. Safety rating at normal doses is 9 out of 10.

What should you not take with L-Isoleucine?

Separate it from Tryptophan, Other Large Amino Acids by two to four hours. High isoleucine may reduce tryptophan uptake into brain

Does L-Isoleucine interact with medications?

Documented interactions with diabetes-medications, diazoxide. Discuss these with a pharmacist before combining.

How do you know if you need L-Isoleucine?

The marker is Plasma isoleucine levels, optimal range 60-120 μmol/L. Common deficiency signs: Muscle weakness and fatigue, Poor exercise endurance, Slow muscle recovery, Impaired wound healing.

Taken for

62 Energy & Metabolism

Vitamin B12 (Methylcobalamin) · Ashwagandha · Vitamin B12 (Cyanocobalamin)

 43 Performance

Caffeine · Creatine Monohydrate · Whey Protein