6 min read
L-Carnitine: Effect on Fat Burning and What Research Shows
How L-carnitine works in the body, why its reputation as a fat burner does not hold up in research and what is actually measurable in endurance sport.
L-carnitine is among the best-known dietary supplements when it comes to fat burning and weight loss. Hardly any other substance is advertised so often with the promise of converting excess fat into energy in a targeted way. What actually lies behind this substance made by the body is more nuanced than advertising often suggests.
This guide explains what L-carnitine does in the body, how it relates to fat burning, what research shows on its effect in weight loss and how to put it into perspective.
01
What is L-carnitine?
L-carnitine is an amino acid-like substance made by the body, formed mainly in the liver and kidneys from the amino acids lysine and methionine. Most of the body's own carnitine is found in skeletal muscle and heart muscle, because carnitine is needed there to transport fatty acids into the mitochondria, the power plants of the cells where energy is produced.
In addition to the body's own production, you take in carnitine through food, mainly through red meat and in smaller amounts through fish and dairy products. A healthy organism normally produces enough carnitine itself, so a true deficiency is rare in healthy people with a balanced diet. A carnitine deficiency caused by illness is rare and is diagnosed and treated medically, and it has little to do with the supplementation discussed in sport.
The following table shows typical orders of magnitude of the carnitine content of some foods per 100 grams, as found in nutrient tables.
| Food | Carnitine per 100 g (approx.) |
|---|---|
| Beef | 60 to 100 mg |
| Lamb | 80 to 200 mg |
| Pork | 20 to 30 mg |
| Chicken breast | 5 to 10 mg |
| Fish | 3 to 10 mg |
| Milk | 2 to 5 mg |
| Plant-based foods | under 1 mg |
This overview makes clear why a predominantly plant-based diet comes with a considerably lower dietary carnitine intake than a meat-heavy diet. Since the body can produce carnitine itself when needed, however, this is generally not a problem in healthy people.
Matching productGlycineAmazon →
02
How does L-carnitine relate to fat burning?
The biochemical mechanism on which the marketing of L-carnitine as a fat burner is based is real in principle: carnitine is indeed needed to transport fatty acids into the mitochondria, where they are used to produce energy. From this, the conclusion is often drawn that more carnitine automatically leads to more fat burning.
This conclusion is too simple, however. In healthy people, the carnitine concentration in muscle is generally already high enough, so fatty acid transport is not the limiting factor for fat burning. Additional intake from outside hardly raises the carnitine content in muscle in most people, as uptake into muscle cells is regulated within limits.
03
What research says about L-carnitine and weight loss
Several systematic reviews and meta-analyses have examined whether additional L-carnitine helps with weight loss. The overall result is sobering: if anything, only small, often statistically weak effects on body weight appear, which are hardly noticeable in practice and considerably smaller than what can be achieved by adjusting your diet and moving more.
As a sole means of losing weight, L-carnitine is therefore not suitable. A dietary supplement like L-carnitine does not replace a balanced diet or a calorie deficit, which is ultimately what decides weight loss. Some studies in which an effect was observed additionally combined intake with a structured training programme, so the observed changes cannot be attributed with certainty to carnitine alone.
04
L-carnitine in endurance sport
Besides weight loss, L-carnitine is also discussed in endurance sport, for example in connection with recovery and muscle soreness. Some smaller studies point to possible positive effects on markers of muscle damage after intense exertion, but the results are not consistently uniform and are mostly limited to specific training situations.
For pure endurance performance, such as times or maximal oxygen uptake, most controlled studies could not show a clear advantage from additional L-carnitine over placebo when carnitine status was already normal.
Of interest are a few studies in which carnitine was given together with carbohydrates over several weeks to improve uptake into muscle cells via an insulin effect. Such protocols showed measurable changes in muscle carnitine content in small studies in some cases, but they are laborious, unrealistic and hardly transferable to normal everyday training. For most athletes, the practical benefit of simple supplementation therefore remains limited.
05
Use and dosage
L-carnitine products come as capsules, tablets or liquid, often also as L-carnitine tartrate or acetyl-L-carnitine. In studies, amounts in the range of about 500 to 2000 mg daily were mostly used, often over several weeks. This figure serves only as a rough guide, and what counts is always the serving recommendation on the respective packaging.
A possible time window for an effect is more likely weeks than days, since studies on carnitine loading of muscle were mostly designed to run for two to three months. A short-term intake before a single training session or competition is therefore not well justified.
Whether L-carnitine is taken before or after training plays no decisive role from a scientific point of view, as it is not a short-acting source of energy but a transport substance, whose possible benefit, if present at all, shows itself more over a longer period.
Various forms of carnitine are also found in shops, most commonly plain L-carnitine, L-carnitine tartrate and acetyl-L-carnitine. L-carnitine tartrate is a form bound to tartaric acid that is common mainly among athletes, while acetyl-L-carnitine additionally carries an acetyl group and is discussed in connection with the nervous system. For the basic function in fat metabolism, the forms differ little in practice, with the differences lying more in absorption and in their respective research focus. None of these forms removes the fundamental limitation: in adequately supplied, healthy people, the additional benefit of supplementation remains limited, regardless of which form is chosen.
06
Tolerability and side effects
L-carnitine is generally considered well tolerated at the usual amounts. At higher doses, gastrointestinal complaints or an unpleasant body odour can occasionally occur, which can arise from the metabolism of carnitine in the gut. With existing thyroid conditions, kidney disease, during pregnancy, breastfeeding or when taking medication, in particular anticoagulants, medical advice beforehand makes sense. Since the body can also form carnitine from the amino acids lysine and methionine, an additional supplement is usually not necessary for healthy people with sufficient protein intake overall.
07
What the research says
The basic mechanism by which L-carnitine acts in fat metabolism is scientifically well understood. The marketing as an effective fat burner derived from it does not hold up against research, however: in healthy, adequately supplied people, additional carnitine shows at most small, clinically hardly relevant effects on body weight or fat burning in studies. Anyone trying L-carnitine should therefore put it into realistic perspective and not see it as the main weight-loss strategy in place of changing your diet and training regularly. As a small, supplementary building block alongside an overall well-thought-out nutrition and training strategy, taking it at usual amounts generally does no harm, but a noticeable independent effect is not to be expected.
08
Frequently asked questions
Does L-carnitine burn fat in a targeted way?
No, targeted, noticeable fat loss from additional L-carnitine alone is not scientifically proven. The mechanism is real but, in most healthy people, is not the limiting factor of fat burning.
When should you take L-carnitine?
A specific time of intake is not decisive, as it is not a short-term energy boost. Regular intake over several weeks matters more than the exact time of day.
Does everyone need additional L-carnitine?
No, the body normally produces enough carnitine itself with a balanced diet. An actual deficiency is rare in healthy people.
Does L-carnitine make sense for vegans?
Since carnitine occurs mainly in meat, dietary intake is lower on a purely plant-based diet. The body can, however, produce carnitine itself from lysine and methionine, so a deficiency is rare here too.
Explore
Read next
Protein types at a glance: whey, casein, plant-based and moreAn overview of all common protein types from whey to collagen, with a comparison table and links to detailed guides.
Amino Acids: The Building Blocks of ProteinStructure, classification and functions of amino acids at a glance, with a table of all 20 proteinogenic amino acids and links to all guide…
Supplements for Sport and Fitness: A Factual OverviewAll supplement categories at a glance, with the evidence rated from good to thin, plus safety and buying tips.