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L-carnitine · Weak evidence
What L-carnitine is for and what the evidence says
The short answer. Carnitine carries fatty acids into the mitochondria, and from that biochemistry fact came the idea that taking it burns fat. The leap does not hold up: in a healthy person the muscle already has plenty of carnitine and transport is not the step limiting anything. Sports nutrition reviews place it among supplements with limited or mixed evidence, for both fat and performance.
Reviews find no consistent effect. It is listed because it sells, not because it works. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.
01 What it does and how much
Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.
| Effect | How much | Detail |
|---|---|---|
| Fat loss | no consistent effect | It is what it is sold for and what does not consistently appear in the reviews. A calorie deficit is still the only thing that decides. [1] |
| Performance | mixed evidence | Some studies on recovery and muscle damage point to something; taken together, they do not allow it to be claimed. [1] |
| Study dose | 2 to 4 g a day | It is the usual regime, and the reference this site uses to judge whether a product reaches the dose it has been studied at. [1] |
| Muscle carnitine | already full | The body makes it and meat provides it. Raising the store with capsules is hard, and that is the mechanistic reason not much happens. [1] |
02 How to take it
- Dose. 2 to 4 g a day is what the studies use, without that meaning it works.
- When. No evidence-backed timing. It is usually recommended before training out of commercial habit.
- How long before you notice it. There is no demonstrated effect to wait for.
Details that change the result
- The tartrate form is the usual one in sport; acetyl-L-carnitine is sold for other uses and is not interchangeable in this context.
- Check the milligrams of carnitine per serving: many liquid vials carry far less than the packaging suggests.
- It is safe and cheap; the argument against it is not risk, it is that the money goes further on creatine or protein.
- Vegetarians and vegans get less from their diet, but that does not translate into a demonstrated benefit from the supplement.
03 When it makes sense and when it does not
Worth it if
- Almost no sports case supports it. It is listed because it sells a lot, not because it works.
- On medical advice for real carnitine deficiencies, which are rare and not diagnosed in a gym.
Not worth it if
- To lose fat. What works there is a sustained calorie deficit.
- Before you have protein, creatine, sleep and training covered.
- Relying on a liquid vial that does not declare the milligrams per serving.
04 Sources
Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.
- Kerksick CM et al. ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr. 2018;15:38. La L-carnitina figura entre los suplementos con evidencia limitada o mixta; 2-4 g diarios son la dosis habitual de los estudios. doi:10.1186/s12970-018-0242-y
This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.
Questions about carnitine
Answered with the data on this page
- Does carnitine burn fat?
- Not demonstrably. The idea comes from the fact that it carries fatty acids into the mitochondria, but in a healthy person that transport is not the limiting step and the muscle already has plenty of carnitine. Sports nutrition reviews find no consistent effect on fat loss.
- How much carnitine should you take a day?
- Studies use 2-4 g a day. That is the dose it has been researched at, not a dose with a demonstrated effect, and this site uses it only to judge whether a product reaches or falls short of what was studied.
- What is the difference between L-carnitine tartrate and acetyl-L-carnitine?
- Tartrate is the usual form in sports supplementation. Acetyl-L-carnitine crosses the blood-brain barrier more easily and is sold for other purposes, so they are not interchangeable. For neither of them is the sports evidence strong.
- Then why is it sold so much?
- Because its biochemical mechanism can be explained in one sentence and sounds convincing: it carries fat to be burned. The leap from that sentence to "it makes you lose weight" was never shown, but by then it was already the star ingredient on the fat burner shelf.
And now, which to buy
Prices, kept apart from the evidence
This page explains what carnitine does and deliberately names no brand. The comparison is the other half: 93 products from 10 stores from €0.055 per capsule, sorted by price and by how verifiable their certification is.
Other guides
What each supplement does, with its sources