What is L-carnitine?
L-carnitine is a quaternary ammonium compound synthesised in the body from lysine and methionine. It functions as a carrier molecule, transporting long-chain fatty acids across the inner mitochondrial membrane where they are oxidised for energy. It is found naturally in red meat and dairy products.
How it works
By facilitating fatty acid transport into mitochondria, L-carnitine theoretically increases fat oxidation during exercise. It may also reduce exercise-induced muscle damage and support recovery. L-carnitine L-tartrate (LCLT) is the form most studied for exercise performance, while acetyl-L-carnitine (ALCAR) has greater relevance to cognitive function.
What the research says
- 2g of LCLT daily for 3 weeks reduced muscle damage markers and improved recovery in resistance-trained men (Volek et al., 2002)
- Fat loss effects are inconsistent — most studies show modest or no significant effect on body composition in healthy individuals
- More effective for individuals with low baseline carnitine levels — vegetarians and older adults show greater response
- Co-ingestion with carbohydrates improves carnitine retention in muscle tissue
Effective dose
1–3g of L-carnitine L-tartrate per day. Effects on fat oxidation require consistent use over several weeks — not an acute fat burner. Taking with a carbohydrate source improves muscle uptake. Expect minimal effect on body composition without a caloric deficit already in place.
What to check on the label
Confirm the form — L-carnitine L-tartrate for performance and recovery; acetyl-L-carnitine for cognitive effects. Generic "L-carnitine" without specification may be less bioavailable. Many fat burner products include carnitine at 500mg or less — below the dose used in research.
Safety
Safe at recommended doses. High doses (3g+) may cause fishy body odour due to gut bacterial metabolism of carnitine to TMAO. Some research suggests TMAO may have cardiovascular implications at chronically high intakes — more research is ongoing.