L-carnitine and acetyl-L-carnitine
Also called: carnitine, L-carnitine tartrate, ALCAR, acetyl-L-carnitine, propionyl-L-carnitine.
A fat transporter sold as a fat burner, which the body makes on its own, and whose effect on weight is counted in one kilogram.
What it is
Carnitine carries long-chain fatty acids into the mitochondria so they can be oxidized there. The liver, kidneys and brain synthesize it from lysine and methionine, and the NIH writes that healthy children and adults do not need to consume it. People buy it for fat loss, performance and, in its acetylated form, for memory.
What the label does not say
- Absorption from a supplement is 14 to 18% according to the NIH (5 to 25% according to the Linus Pauling Institute for doses of 0.6 to 7 g), versus 63 to 75% for carnitine from food. The gram on the label is not the gram absorbed.
- Weight loss: the 2016 meta-analysis cited by the NIH (nine trials, 911 participants) reports 1.33 kg more lost than with placebo. That is the actual data behind the word burner.
- The gut microbiota converts carnitine into TMAO, a pro-atherogenic compound associated with increased cardiovascular risk in a 2013 study cited by the NIH; omnivores produced more of it than vegans. It is a signal, not evidence of harm, but it appears on no label.
- Acetyl-L-carnitine and cognition: a 2003 meta-analysis (21 trials, 1.5 to 3 g per day) reported better clinical scores, but a Cochrane review concludes that routine use against dementia is not justified, and the Linus Pauling Institute notes that the larger trials found little or no effect.
The forms on the shelf
- L-carnitine and its salts (tartrate, fumarate): the forms covered by the Health Canada monograph for recovery and training support.
- Acetyl-L-carnitine (ALCAR): the form studied for cognition; it is not among the source ingredients in the Canadian L-carnitine monograph.
- Propionyl-L-carnitine: studied mostly in cardiology.
- D-carnitine or DL-carnitine: the Linus Pauling Institute warns that the D isomer competes with L-carnitine for absorption and can create a deficiency.
Published reference values
- No recommended intake: a meat-containing diet provides 24 to 145 mg per day for a 75 kg person, a vegan diet about 1.2 mg, and synthesis covers the need.
- Trial doses: 1.8 to 4 g per day for weight, 1 to 4 g for exercise, 1.5 to 3 g of acetyl-L-carnitine for cognition. Health Canada caps it at 4 g per day and 2 g per dose.
- Around 3 g per day, the NIH reports nausea, vomiting, cramps, diarrhea and a fishy body odour.
- On performance, controlled trials most often report no effect on VO2max, lactate or performance according to the Linus Pauling Institute.
When
The Canadian monograph indicates 2 to 4 hours before exercise for the performance claims. No comparison between liquid and capsules was found in a source acceptable here; what counts is the number of grams of L-carnitine per serving.
Keep apart from
- Valproic acid, phenobarbital, phenytoin, carbamazepine: these anticonvulsants lower blood carnitine; this is a matter of medical monitoring, not spacing.
- Pivalate-containing antibiotics in prolonged use: carnitine depletion reported.
To mention to a professional
- Seizure disorder (a Health Canada warning), kidney failure or dialysis, cardiovascular disease (the TMAO signal), pregnancy and breastfeeding: check with a health care professional.
What it is sold for, and what the data show
Carnitine is sold as a fat burner and performance support. The trials show about 1.3 kg more in weight loss, no clear effect on performance and mixed results on cognition for the acetylated form. Someone who eats meat already has it, and someone on a vegan diet synthesizes enough according to the Linus Pauling Institute.
From the plate first
According to the NIH: beef steak 42 to 122 mg per 3 ounces, ground beef 65 to 74 mg, whole milk 8 mg per cup, chicken breast 2 to 4 mg, cod 3 to 5 mg.
Sources
- NIH Office of Dietary Supplements, Carnitine (Health Professional)
- Linus Pauling Institute, Micronutrient Information Center, L-Carnitine
- Health Canada, natural health product monograph, L-Carnitine
- NIH Office of Dietary Supplements, Dietary Supplements for Weight Loss (Health Professional), carnitine section
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.