Supporting Energy Production: L-Carnitine

An in-depth look at the types, benefits and side effects of L-carnitine.

Supporting Energy Production: L-Carnitine photo

An amino acid touted for its weight loss and fitness benefits, carnitine, plays an important role in the conversion of fat into energy. While this sounds promising, consideration needs to be paid to the type of carnitine, how it works and the side effects, if any.

What is Carnitine?

Carnitine is found in nearly all cells of the body and abundantly in skeletal and heart muscle. It occurs as two forms, D and L. Only L-carnitine is active in the body and is the form found in food sources. L-carnitine is an amino acid itself made from two other amino acids, L-methionine, and L-Lysine which we get from protein-rich food sources such as meat, eggs, fish and soy. L-carnitine is made in the liver and kidneys and requires iron, vitamin B6, and niacin as co-factors.1

Generally, the body can produce enough L-carnitine, but in some cases an individual’s need for the amino acid outweighs the amount produced and they require an additional supply from food or oral supplementation, therefore making L-carnitine a conditionally essential nutrient.

Unabsorbed L-carnitine is mostly degraded by gut bacteria in the large intestine.

Food sources of L-carnitine

Carnitine is derived from the Latin word “carnus” as the compound was first isolated from meat in 1905. L-carnitine is particularly abundant in red meat, and in particular beef. It is also found in lesser amounts in the likes of poultry, fish, poultry, and milk. Vegetarian sources include foods such as tempeh, asparagus, avocados, and peanut butter.

There is no recommended daily intake. Omnivorous diets that include red meat, fish, poultry, and dairy products provide about 60 to 180 mg per day. A vegan diet normally provides between 10 and 12mg per day.2

Supplementation of L-carnitine at doses of 2 grams or less per day seem to be well tolerated and safe for most adults.

Variations of L-carnitine

Most variations of L-carnitine are a laboratory synthesised compounds that uses naturally sourced carnitine as an ingredient. Depending on the type of molecule the L-carnitine is bound to it can have different health benefits.

  • L-carnitine can be found as Acetyl-L-carnitine (ALCAR) which is L-carnitine bound to an acetyl group. This form of L-carnitine is known for supporting brain health as it can easily pass through the blood brain barrier.3 The acetyl group ensures that acetyl-L-carnitine is active in the brain and nerves making it beneficial for use in neurodegenerative conditions. This variation is synthetically produced in a laboratory and available in supplemental form.
  • L-carnitine L-tartrate (LCLT) is bound to tartaric acid and is the common form of L-carnitine supplementation amongst athletes. Due to it being absorbed faster than any other form of L-carnitine, it is most often used in supplements suitable for pre- and post-workouts. It has also been shown to be effective in combatting aching muscles and recovery after exercise.4
  • Glycine propionyl-L-carnitine (GPLC) is a form of L-carnitine bound to glycine and is a good option for individuals with circulatory issues.5 Many people use this form of L-carnitine in supplement form for leg pain, to increase blood flow, and even to support low testosterone levels in older adults.
  • L-carnitine Fumarate is bound to fumaric acid. This form is widely used as an energy booster and to assist with weight loss.

Why is L-carnitine important in the body?

Mitochondria, often referred to as the powerhouses of the cell, are small components of our cells where the production of energy takes place. L-carnitine acts as a shuttle, transporting fatty acids into the mitochondria in the cells which is then used to metabolise energy.

Cellular waste is produced as a result of this metabolic process. L-carnitine has the additional beneficial role in assisting with the removal of cellular waste by transporting the toxic materials out of the mitochondria, to prevent their accumulation. Therefore, in addition to its vital role in energy production, L-carnitine is also a great antioxidant.

L-carnitine deficiency

There are two distinct L-carnitine deficiency states, known as "primary" and "secondary" carnitine deficiency.

  • Primary carnitine deficiency is due to a rare genetic disorder leading to a severe systemic carnitine depletion. Primary carnitine deficiency occurs in 1-5 per 10, 000 population and most commonly manifests between ages 1-7 years old.6
  • Secondary carnitine deficiency is less severe with respect to its short-term clinical impact and is much more common. This state of deficiency occurs due to, or in association with, other disorders such as liver or kidney disease, defects in fatty acid metabolism, or side effects from medication.6

Reduced plasma carnitine levels have been noted in malnourished children and adults. Levels generally improve with dietary intervention.7

Vitamin B-12 deficiency has been linked with an increase in the loss of natural levels of carnitine. Supplementing L-Carnitine and Methyl B-12 together may therefore improve energy utilisation and enable the body to burn fat more efficiently.8

Some signs of L-carnitine deficiency are fatigue, muscle weakness, decreased muscle tone, irritability, and low blood sugar. Although these symptoms are similar to several other conditions too.

7 benefits of L-carnitine

L-carnitine is approved for treatment in primary and certain secondary carnitine-deficiency syndromes. There are several studies that have shown favourable outcomes supporting the use of supplementation of L-carnitine.

1. Antioxidant properties of L-carnitine

Since L-carnitine has the additional role in supporting the removal of cellular waste, it ultimately serves in protecting cells and DNA from damage. In a randomised placebo-controlled trial, L-carnitine supplementation at a dose of 1000 mg per day was associated with a significant reduction in oxidative stress and an increase in antioxidant enzymes activities in coronary artery disease.9

2. Increased energy production from L-carnitine

In a one-month study, 66 elderly participants who were 100 years or older ingested two grams of L- carnitine to assess for muscle mass, lipid profile and rapid muscle fatigue. At the end of the study the participants reported an increase in muscle mass and energy levels.10

3. Heart health and L-carnitine

A systemic review and meta-analysis by the Mayo clinic found that compared with the control group, those in the study that supplemented with L-carnitine was associated with a 27% reduction in all-cause mortality, and a 40% reduction in the development of angina.11

4. L-carnitine and post-work out recovery

A review of L-carnitine supplementation in recovery after exercise positively demonstrated that L-carnitine alleviates muscle injury and reduces markers of cellular damage as well as reducing muscle soreness.4

5. Men’s fertility and L-carnitine

The results of a study from 2011 suggested that L-carnitine level in seminal plasma plays an essential role in maintaining male fertility. The study showed that L-carnitine led a significant increase in the percentage of motile testicular sperm.12

6. Weight loss and L-carnitine

Another 2011 study showed that supplementation with L-carnitine for 6 months lead to a 21% increase in carnitine stores within the muscle.13 This translates to a 21% increase in fat utilisation due to the increase in L-carnitine being able to shuttle the fat into the cells. Not only does this improve energy production, but essentially it decreases the amount of fat that your body stores. It’s important to note that L-carnitine will not help in weight loss if not combined with a healthy diet and exercise regime.

7. Hyperthyroidism support and L-carnitine

Some clinical evidence suggests that L-carnitine may improve symptoms of hyperthyroidism, such as a rapid heartbeat, nervousness, and weakness. The mechanism isn’t fully understood but one theory suggests that l-carnitine prevents the entry of thyroid hormones (T3 and T4) into the body’s cells. In one randomised trial, supplementing with 2 and 4 grams per day of L-carnitine reversed hyperthyroid symptoms in the trial’s participants. In another study, L-carnitine relieved a “thyroid storm”.14 Based on this information, taking L-carnitine might make symptoms of hypothyroidism worse.

Side effects of L-carnitine supplementation

The adverse effects of oral L-carnitine are mild and rare. It has been reported to cause vomiting, diarrhoea, a fishy body odour, abdominal cramps, and nausea.

A 2013 study in mice suggested that L-carnitine is metabolised into a compound called TMAO (Trimethylamine N-oxide), which changes cholesterol metabolism and may promote plaque build-up in the arteries. However, to date, no human studies suggest that L-carnitine worsens cardiovascular health.15

L-carnitine supplementation in breast-feeding mothers has not been clinically studied, therefore it is not advised to take if breastfeeding.


It is commonly accepted that L-carnitine has the ability to move more fatty acids into the mitochondria in the cells to be used in energy production, making it an effective performance enhancer, and it may also be beneficial for fat burning and weight loss.

There are various forms of L-carnitine, each with a unique set of benefits. Supplementation may benefit individuals who don’t easily acquire it from natural food sources as a part of their normal diet.

Before taking any supplements, it is always advisable to speak to a qualified practitioner.

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  1. Hanai, T. Shiraki, M. Imai, K. et al. (2020),’Usefulness of Carnitine Supplementation for the Complications of Liver Cirrhosis’, Nutrients, 12(7), pp. 1915.
  2. Rebouche, C. (2004),’Kinetics, pharmacokinetics, and regulation of L-carnitine and acetyl-L-carnitine metabolism’, Ann NY Acad Sci, 1033, pp. 30-41.
  3. Brooks, J. Yesavage, J. Carta, A. et al. (1998),’Acetyl L-Carnitine Slows Decline in Younger Patients With Alzheimer's Disease: A Reanalysis of a Double-Blind, Placebo-Controlled Study Using the Trilinear Approach’, International Psychogeriatrics, 10(2), pp. 193-203.
  4. Fielding, R. Riede, L. Lugo, J. et al. (2018),’l-Carnitine Supplementation in Recovery after Exercise’, Nutrients, 10(3), pp. 349.
  5. Wiseman, L. and Brogden, R. (1998),’Propionyl-L-carnitine’, Drugs Aging, 12(3), pp. 243-248.
  6. Flanagan, J. Simmons, P. Vehige, J. et al. (2010),’Role of carnitine in disease’, Nutr Metab, 7, pp. 30.
  7. Khan, L. and Bamji, M. (1979),’Tissue carnitine deficiency due to dietary lysine dificiency: triglyceride accumulation and concomitant impairment in fatty acid oxidation’, J Nutr, 109, pp. 24-31.
  8. Brass, E. and Stabler, S. (1988),’Carnitine metabolism in the vitamin B-12-deficient rat’, Biochem J, 255(1), pp. 153-159.
  9. Lee, B. Lin, J. Lin, Y. et al. (2014),’Effects of L-carnitine supplementation on oxidative stress and antioxidant enzymes activities in patients with coronary artery disease: a randomized, placebo-controlled trial’, Nutr J, 13, pp. 79.
  10. Pistone, G. Marino, A. Leotta, C. et al. (2003),’ Levocarnitine administration in elderly subjects with rapid muscle fatigue: effect on body composition, lipid profile and fatigue’, Drugs Aging, 20(10), pp.761-767.
  11. DiNicolantonio, J. Lavie, C. Fares, H. et al. (2013),’ L-Carnitine in the Secondary Prevention of Cardiovascular Disease: Systematic Review and Meta-analysis’, Mayo Clinic Proceedings, 88(6), pp. 544 – 551.
  12. Ahmed, S. Karira, K. Jagdesh, A. (2011),’Role of L-carnitine in male infertility’, J Pak Med Assoc, 61(8), pp. 732-736.
  13. Sahlin, K. (2011),’Boosting fat burning with carnitine: an old friend comes out from the shadow’, J Physiol, 589(7), pp. 1509-1510.
  14. Benvenga, S. Amato, A. Calvani, M. et al. (2004),’Effects of carnitine on thyroid hormone action’, Ann N Y Acad Sci, 1033:158-167.
  15. Koeth, R. Wang, Z. Levison, B. et al. (2013),’Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis’, Nat Med, 19(5), pp. 576-585.