amino acid · for low stamina
L-Carnitine
Helps you burn fat during exercise, sparing the stored carbohydrate you need later.
Say that in clinical terms
Increases fat oxidation during exercise, sparing muscle glycogen. Reduces lactate accumulation.
How strong is the research?
21 men did 24 weeks of interval training with or without carnitine. Both groups improved the same.
6 papers read, 3 supporting, 2 against.
Who was studied: Nine people. Too few to say who this applies to.
How much to take
daily
1000–2000 mg
L-carnitine tartrate most studied for exercise. Take with carbohydrates to enhance uptake.
Before you take it
- No NIH ODS Tolerable Upper Intake Level (UL) has been established for L-carnitine; long-term safety data at doses above 2g/day are limited.
- GI adverse effects at doses ≥3g/day: nausea, vomiting, abdominal cramps, diarrhea, and fishy body odor; effects are dose-dependent and related to TMAO production.
- TMAO cardiovascular risk: L-carnitine is converted by gut microbiota to trimethylamine (TMA), then by hepatic flavin monooxygenases to trimethylamine-N-oxide (TMAO); elevated TMAO is associated with accelerated atherosclerosis in animal models and with increased major adverse cardiovascular event risk in humans with concurrently high TMAO levels (Koeth et al. 2013, Nature Medicine; acknowledged by NIH ODS fact sheet); omnivores produce substantially more TMAO from the same L-carnitine dose than vegans or vegetarians.
- Warfarin/oral anticoagulant interaction: a single case report documents INR elevation from stable range (1.99–2.94) to 4.65 after a patient with a mechanical aortic valve added L-carnitine to stable warfarin therapy; no RCT evidence confirms this interaction; INR monitoring is prudent if co-administering; evidence quality is case-report only.
- Pivalate-conjugated antibiotics (pivampicillin, pivmecillinam): chronic co-administration may deplete carnitine stores (NIH ODS); this is a carnitine-depletion interaction, not a chelation/timing interaction.
- Anticonvulsants (valproic acid, phenobarbital, phenytoin, carbamazepine): chronic use may reduce carnitine levels; supplemental carnitine may be indicated but should be discussed with prescriber (NIH ODS).
What we make of it
Nine people, and the mechanism is disputed in people who are not deficient.
The detail
Nine participants is far too few to derive a reliable effect. The idea that it spares fuel and reduces lactate is contested in healthy adults who are not carnitine-deficient.