Instant overview
L-carnitine is a naturally occurring compound that transports long-chain fatty acids into the mitochondria of muscle cells, where they are burned for energy6 It may support weight loss by increasing calorie expenditure and allowing longer training sessions, and has been associated with reduced muscle soreness and faster recovery6,7 A systematic review by the Mayo Clinic associated carnitine supplementation with a 27% reduction in all-cause mortality3 - The two main supplement forms are L-carnitine tartrate (fast absorption, common in sports nutrition) and acetyl L-carnitine (ALCAR), the most bioavailable form
L-carnitine is a naturally occurring compound that transports long-chain fatty acids into the mitochondria of muscle cells, where they are burned for energy. It may support weight loss, exercise performance, and recovery, and has been associated with heart health benefits. It is found in red meat, fish, and dairy, and is also available as a supplement.
L-carnitine: at a glance
| Aspect | Detail | Recommendation |
|---|---|---|
| What it does | Transports long-chain fatty acids into muscle cell mitochondria to be burned for energy6 | — |
| Weight loss | May increase calorie expenditure and allow longer training sessions6 | Supplement alongside a healthy diet and exercise programme |
| Exercise recovery | Reduces markers of muscle damage after high-intensity exercise7 | 2-4g daily6 |
| Key food sources | Red meat, fish, dairy, and poultry; small amounts in nuts, seeds, avocado, and asparagus | — |
| Main supplement forms | L-carnitine tartrate (fast absorption) and acetyl L-carnitine / ALCAR (most bioavailable) | See dosage section for optimal amounts |
Jump to:
- What is L-carnitine?
- What does L-carnitine do?
- Benefits of L-carnitine
- How does L-carnitine work?
- Types of L-carnitine and their uses
- L-carnitine dosage
- When should you take L-carnitine?
- Which foods contain L-carnitine?
- L-carnitine side effects
- Frequently asked questions
What is L-carnitine?
It's a non-essential amino-acid-like compound, meaning it's produced in the body naturally.
You can get a certain amount of L-carnitine from your diet, as it's found in foods such as red meat — typically the redder the meat, the better. Plant sources such as avocado and soybean contain small amounts too.
Supplements should be consumed alongside a healthy diet, but are often recommended to anyone who struggles to get enough of a certain nutrient in their diet.5
What does L-carnitine do?
L-carnitine is responsible for transporting long-chain fatty acids to your cells' mitochondria, where energy is then produced as the fat is oxidised and used for fuel. More than 95% of the body's L-carnitine stores are found in skeletal muscle (muscle which is connected to your skeleton), along with trace amounts in the liver and blood.6
Benefits of L-carnitine
1. L-carnitine may aid weight loss
It's been theorised that L-carnitine could help your body to produce energy by utilising the body's fat stores, allowing you to work out for longer and ultimately aiding in fat loss. Evidence suggests it may promote weight loss by increasing calorie expenditure.6
Taking an L-carnitine supplement daily has been proven to increase the blood and muscular concentrations of this amino acid-like compound, which could enhance fat metabolism as a result with increased muscle carnitine concentrations.6
2. L-carnitine may improve exercise performance & recovery
Given its potential fat-burning capabilities, it's thought that L-carnitine optimises how your body uses fat for fuel, allowing you to exercise for longer.7 Some research has also found that three weeks' supplementation with an L-carnitine supplement reduces muscle damage from high-intensity exercise bouts.7
Supplementing with L-carnitine could also play an important role in recovery from strenuous exercise, with suggested doses of 2-4g daily to optimise results.6 There's initial evidence that this could lead to a reduction in various markers of metabolic stress and muscle soreness which is replicated in many studies. However, research is still limited and further studies are needed.2
3. L-carnitine may support heart health
Research supports medically supervised use of L-carnitine for treating cardiac related issues and is often given by IV by a medical professional. It may boost energy levels as it increases the amount of fuel availability that the heart requires to function.3 In a systematic review by the Mayo Clinic, carnitine was associated with a 27% reduction in all-cause mortality.3
L-carnitine may also play a role in keeping cholesterol levels in a healthy range.4
How does L-carnitine work?
When you exercise, thousands of biochemical reactions are taking place inside your body. One of these is the action of your enzymes starting to break down stored fat into fatty acids and glycerol, a sugar alcohol. These are then used as fuel throughout exercise.
Studies have theorised that L-carnitine is a compound that plays an important role in this process of fat metabolism as its key role is to transport the long-chain fatty acids across the inner membrane. These fatty acids are thought to be the main energy sources used during low- to moderate-intensity exercise.2
Types of L-carnitine and their uses
The two main variations of L-carnitine that are supplemented in the diet are L-carnitine tartrate and acetyl L-carnitine.
1. L-carnitine tartrate
L-carnitine tartrate is one of the most common forms of L-carnitine found in sports nutrition supplements due to its rapid absorption rate.9 It's created in the body from the amino acids lysine and methionine and is mainly synthesised in the liver and kidneys before being transported for use in other tissues in the body.
L-carnitine tartrate is found in its highest levels in tissues that use fatty acids as the main fuel source, such as the skeletal and cardiac muscles. It should be taken in conjunction with a healthy, balanced diet and exercise regime.3
2. Acetyl L-carnitine (ALCAR)
Acetyl L-carnitine is created in the body from the amino acids lysine and methionine. ALCAR has an acetyl group attached to the carnitine molecule. This allows it to pass through the blood-brain barrier making it the most bioavailable, and thus most easily absorbed, form.
ALCAR is ideal for athletes and active people who take part in regular exercise or anyone looking for an easy-to-consume source of L-carnitine that can be taken throughout the day.4
Dosage — how much L-carnitine should you take?
Studies suggest varying doses for each form of L-carnitine for best results. The following is deemed optimal for each form:5
Acetyl-L-carnitine: 600-2,500mg per day.L-carnitine L-tartrate: 1,000-4,000mg per day.Propionyl-L-carnitine: 1,000-4,000mg per day.
When should you take L-carnitine?
If your plan is to use this supplement to optimise energy during your workout, it's best to take it prior to working out. Most scientific studies recommend taking L-carnitine about one hour prior to exercise. However, if you want to take advantage of the other benefits (recovery and weight loss support), taking it after exercise can also be effective.
Which foods contain L-carnitine?
Although this supplement can be made by the body, you can also up your L-carnitine intake from your diet. It's highest in animal products like beef, lamb, pork, poultry, fish, and dairy products.
Whey (made from milk) naturally contains some L-carnitine, and plant-based sources contain it in small amounts, like nuts, seeds, whole grains, and some fruits and vegetables (like avocados and asparagus).
L-carnitine side effects
Side effects of this supplement are mild because it's naturally found in our food. Following dosage recommendations did not show serious adverse side effects when taken for less than 12 months, but included stomach upset, breath and urine odour, and seizures in some cases.
Consult a GP if you're considering L-carnitine.5
Take home message
It's been suggested that L-carnitine has the ability to move more fatty acids into your cells to be burnt for energy, making it an effective performance enhancer, and it may also be beneficial for fat burning and weight loss.
While there are some positive results with L-carnitine supplementation, it must be considered that the overall scientific evidence is lacking.
The various forms of L-carnitine are perfect supplements for people who don't easily acquire it from natural food sources as a part of their normal diet.
For those using L-carnitine to support training performance and recovery, pairing it with a quality protein supplement is a sensible addition — whey protein is the most popular choice, and a whey and collagen blend is worth considering if supporting joints and connective tissue alongside muscle is also a priority.
Frequently asked questions
When is the best time to take L-carnitine?
One hour before exercise is the recommended timing for optimising energy during a workout, taken alongside fast-acting carbohydrates. Whether it is taken pre- or post-workout isn't considered an important factor, and taking it after exercise can also be effective for recovery and weight loss support.
What is L-carnitine?
L-carnitine is a non-essential amino-acid-like compound, responsible for transporting long-chain fatty acids to your cells' mitochondria, where energy is produced from the fat's oxidation. More than 95% of the body's stores are found in skeletal muscle.6
What are the benefits of L-carnitine?
Three main benefits are suggested by research: potential weight loss support through increased calorie expenditure, improved exercise performance and recovery through reduced muscle damage markers, and heart health support — with one systematic review associating carnitine with a 27% reduction in all-cause mortality.3
How does L-carnitine work?
L-carnitine works by transporting long-chain fatty acids across the inner membrane of the mitochondria, where they are used as fuel. These fatty acids are thought to be the main energy source during low- to medium-intensity exercise.2
What types of L-carnitine are there?
Two main types are commonly supplemented: L-carnitine tartrate, a common form found in sports nutrition supplements due to its rapid absorption rate, and acetyl L-carnitine (ALCAR), the most bioavailable form, which can cross the blood-brain barrier and is ideal for athletes and active people.4,9
Claire is a Registered Dietitian through the Academy of Nutrition and Dietetics and a board-certified Health and Wellness Coach through the International Consortium for Health and Wellness Coaching. She has a Bachelor of Science in Biology and a Master’s degree in Clinical Dietetics and Nutrition from the University of Pittsburgh.
Talking and writing about food and fitness is at the heart of Claire’s ethos as she loves to use her experience to help others meet their health and wellness goals.
Claire is also a certified indoor cycling instructor and loves the mental and physical boost she gets from regular runs and yoga classes. When she’s not keeping fit herself, she’s cheering on her hometown’s sports teams in Pittsburgh, or cooking for her family in the kitchen.
Find out more about Claire’s experience here.
- Dambrova, M., & Liepinsh, E. (2015). Risks and benefits of carnitine supplementation in diabetes. Experimental and Clinical Endocrinology & Diabetes, 123, 95-100.
- Fielding, R., Riede, L., Lugo, J., & Bellamine, A. (2018). l-Carnitine supplementation in recovery after exercise. Nutrients, 10, 349.
- Lee BJ, Lin JS, Lin YC, Lin PT. Effects of L-carnitine supplementation on lipid profiles in patients with coronary artery disease. Lipids Health Dis. 2016;15:107.
- Cruciani, R. A., Dvorkin, E., Homel, P., Malamud, S., Culliney, B., Lapin, J., … & Esteban-Cruciani, N. (2006). Safety, tolerability and symptom outcomes associated with L-carnitine supplementation in patients with cancer, fatigue, and carnitine deficiency: a phase I/II study. Journal of pain and symptom management, 32(6), 551-559.
- Peeling, P., Binnie, M. J., Goods, P. S., Sim, M., & Burke, L. M. (2018). Evidence-based supplements for the enhancement of athletic performance. International Journal of Sport Nutrition and Exercise Metabolism, 28, 178-187.
- Stephens, F. B., Wall, B. T., Marimuthu, K., Shannon, C. E., Constantin‐Teodosiu, D., Macdonald, I. A., & Greenhaff, P. L. (2013). Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans. The Journal of Physiology, 591, 4655-4666.
- Volek, J. S., Kraemer, W. J., Rubin, M. R., Gómez, A. L., Ratamess, N. A., & Gaynor, P. (2002). L-Carnitine L-tartrate supplementation favourably affects markers of recovery from exercise stress. American Journal of Physiology-Endocrinology and Metabolism, 282, 474-482.
- Wall, B. T., Stephens, F. B., Constantin‐Teodosiu, D., Marimuthu, K., Macdonald, I. A., & Greenhaff, P. L. (2011). Chronic oral ingestion of l‐carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. The Journal of Physiology, 589, 963-973.
- Eder, K., Felgner, J., Becker, K., & Kluge, H. (2005). Free and total carnitine concentrations in pig plasma after oral ingestion of various L-carnitine compounds. International journal for vitamin and nutrition research, 75(1), 3-9.
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