L-carnitine research, summarised honestly
L-carnitine carries long-chain fatty acids across the inner mitochondrial membrane so they can be
oxidised. That one job puts it in the middle of fat metabolism, which is why it turns up in research
on liver fat, body weight, kidney disease, and exercise physiology. It is also why the marketing
around it is frequently ahead of the evidence.
This page summarises published research. It describes what studies have reported. It is not a claim about any product sold by Injectify, and it is not guidance for use in humans.
Start here
- L-carnitine injection compared with oral
supplements. Route changes how much actually reaches your bloodstream, and it is the reason two
studies can disagree about the same question. - L-carnitine and fatty liver disease. The pooled numbers,
including the endpoint that did not reach significance. - L-carnitine and body weight. There is a
measured effect. It is about 1.3 kg, and it shrinks the longer trials run. - L-carnitine and growth hormone deficiency.
A small literature, and worth reading precisely because it is small.
The one fact that explains most of the confusion
Oral carnitine is poorly absorbed. Supplement doses between 0.5 and 6 g land somewhere around
14 to 18 percent bioavailability, while carnitine that arrives as part of food is absorbed at
54 to 87 percent. Swallow 2 g of carnitine and roughly 300 mg of it gets in.
The rest does not vanish. It reaches the large intestine, where gut bacteria get to it first.
That is the mechanism behind most of the apparent contradictions in this literature, and it is
covered in more detail on the route
comparison page.
Two questions to ask of any carnitine study
Which route did it use, and what was the baseline carnitine status of the people in it. Effects
reported in carnitine-depleted populations frequently fail to reproduce in people who already have
plenty, which makes sense if you think about what carnitine does. Topping up a system that is not
short of anything does not speed it up.
The second thing is trial size. A lot of the work here is small, and heterogeneity between
studies is high. When you see a pooled estimate, read the confidence interval rather than the
headline number.
References
- Rebouche CJ. Kinetics, pharmacokinetics, and regulation of L-carnitine and acetyl-L-carnitine metabolism. Ann N Y Acad Sci. 2004;1033:30-41. PMID 15591001
- Koeth RA, Wang Z, Levison BS, Buffa JA, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013;19(5):576-85. PMID 23563705
Research use only. Products discussed on this page are supplied for laboratory research. They are not medicines, not dietary supplements, and not for human or veterinary consumption. Nothing here is medical advice.