L-Carnitine
An amino acid derivative essential for transporting fatty acids into mitochondria for energy production.
L-Carnitine plays a fundamental role in fat metabolism — it acts as a "shuttle" that moves long-chain fatty acids across the mitochondrial membrane so they can be burned for fuel. Popular among athletes and those seeking to improve body composition and endurance.
Evidence Quality
Strong clinical evidence for fat oxidation during exercise, cardiovascular benefits, and muscle recovery. Evidence for weight loss in healthy individuals at rest is weaker — best effects appear with exercise. ALCAR form has additional cognitive evidence.
What Is L-Carnitine?
L-Carnitine is a naturally occurring compound synthesized from the amino acids lysine and methionine. It's found in high concentrations in red meat and dairy. The body stores most carnitine in skeletal muscle, where it is essential for energy production from fats.
Key forms: L-Carnitine L-Tartrate (LCLT) — best for athletic performance; Acetyl-L-Carnitine (ALCAR) — crosses the blood-brain barrier, best for cognitive benefits; Propionyl-L-Carnitine — best for cardiovascular/circulation benefits.
Key Benefits
Fat Burning During Exercise
Increases fat oxidation by up to 55% during moderate-intensity exercise, sparing glycogen and improving endurance performance.
Muscle Recovery
Reduces exercise-induced muscle damage, soreness, and oxidative stress. Supports faster recovery between training sessions.
Cognitive Function (ALCAR form)
Acetyl-L-Carnitine (ALCAR) crosses the blood-brain barrier, supports mitochondrial function in neurons, and may improve focus and memory, particularly with aging.
Cardiovascular Health
Propionyl-L-Carnitine improves blood flow, reduces symptoms of peripheral artery disease, and supports heart muscle energy metabolism.
Dosage & How to Take It
Athletic performance (LCLT)
1,000–4,000 mg per day, taken pre-workout
Cognitive support (ALCAR)
500–2,000 mg per day in the morning
Timing tip
Take with carbohydrates — insulin helps shuttle carnitine into muscle cells, significantly improving absorption.
Contraindications & Cautions
- Thyroid disease (hypothyroidism): L-Carnitine may interfere with thyroid hormone activity — consult your doctor.
- Seizure disorders: ALCAR may lower seizure threshold in people with epilepsy.
- Gut microbiome: L-Carnitine is converted by gut bacteria to TMAO, a metabolite associated with cardiovascular risk in some individuals. Varies by gut flora.
- Anticoagulants: May interact with warfarin — monitor INR levels.
What to Look for When Buying
- Choose the form that matches your goal: LCLT for sport, ALCAR for cognition
- Minimum 1,000 mg per serving — many products underdose
- Third-party tested (Informed Sport or NSF Certified for Sport)
- Capsule or liquid form — both well-absorbed when taken correctly
Where to Buy
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Amazon — L-Carnitine (recommended)
High-potency L-Carnitine L-Tartrate. Ideal for fat burning and exercise performance.
iHerb — L-Carnitine & ALCAR
Wide selection including LCLT and Acetyl-L-Carnitine forms. Ships internationally.