L-Carnitine: Benefits, Risks, and Its Role in Fitness and Weight Loss

Not to be mistaken with creatine, L-carnitine is another popular supplement in the fitness industry due to its performance-boosting and weight-loss-supporting benefits and has been suggested to also have a myriad of other health benefits. But is L-carnitine actually beneficial and worth taking?

The compound can be naturally found in many foods, especially animal products, and is naturally synthesized in the body from amino acids. It comes in several forms and is involved in energy metabolism, hence the performance-boosting benefits.

In this article, I explore the science behind L-carnitine and how the research supports the marketing claims. As a fitness enthusiast with a Master's in Biomedical Sciences, I will break down carnitine deficiency, its health benefits, and supplementation.

What is L-carnitine?

Carnitine is an essential amino acid derivative that plays an important role in energy production. It helps transport long-chain fatty acids into mitochondria, where they are turned into energy via a complex chain of biochemical events. It also helps transport toxic compounds out of the mitochondria. Basically, carnitine helps carry materials required to make fuel into the powerhouse of the cell and helps get rid of the toxic waste made in the process.

Carnitine comes in several forms: L-carnitine, acetyl-L-carnitine, L-carnitine tartrate, and propionyl-L-carnitine. While all forms are naturally found in the body, the science of whether they have different roles is still quite unclear.

Carnitine deficiency

The daily requirement for carnitine is about 15 mg. This includes both dietary intake and endogenous synthesis, and most healthy individuals meet the requirement without much thought. However, carnitine deficiency, primary or secondary, sometimes occurs.

Primary carnitine deficiency

Primary deficiency is caused by a genetic mutation in the carnitine transporter genes. It results in a shortage of carnitine within the cells and defective fatty acid oxidation. The symptoms usually present in infancy or early childhood, with rare cases being asymptomatic until adulthood or at all.

Symptoms of primary carnitine deficiency:

Primary deficiency is typically treated with oral levocarnitine supplementation: 100–200 mg per kg of body weight daily. Supportive outpatient care also includes frequent feeding, and in emergency situations, carnitine supplementation may be combined with carbohydrates to improve the uptake of carnitine into muscles. In more severe cases, hospitalization is needed, and the treatment is tailored based on personal needs, symptoms, and complications.

It is advised to have an emergency letter or card that summarizes key patient information and contact details. If you are experiencing severe or new symptoms, it is crucial to seek professional help immediately.

Secondary carnitine deficiency

Secondary deficiency is caused by other disorders that disrupt endogenous carnitine synthesis or increase its excretion. Causes could include increased renal (liver) excretion, severe malnutrition or malabsorption states, a ketogenic or vegan diet, or being an extremely preterm infant. Certain medications can also lead to a deficiency as they reduce carnitine absorption or increase its excretion.

Symptoms of secondary carnitine deficiency tend to develop over time and include:

• Hyperammonemia encephalopathy (elevated ammonia levels in the brain causing seizures, progressive drowsiness, or even coma)
• Hypoglycemia (low blood sugar)
• Hypoketonemia (low blood ketone levels)
• Hyperuricemia (excess uric acid levels in the blood)
• Myoglobinuria (excess myoglobin levels in the blood)
• Dicarboxylic aciduria (increases urine levels of dicarboxylic acids)
• Muscle weakness
• Anemia
• Fatigue
• Cardiomyopathy

Secondary carnitine deficiency is treated with 20–200 mg of carnitine per kg of body weight daily. The dose and length of supplementation are individual and depend on the severity of the deficiency, its causes, and overall health status.

Benefits of L-carnitine

As we already established, carnitine is essential for energy production, and deficiencies, although not very common, can have serious consequences. L-carnitine is often used by fitness enthusiasts for its potential performance-boosting and weight-loss-supporting properties, and it has been suggested that the compound may be beneficial for heart health.

I will dive into what the science says below.

Heart health

A meta-analysis of 17 randomized controlled trials involving individuals over 18 years old with chronic heart failure examined the effects of daily L-carnitine supplementation ranging from 1.5 to 6 grams. The findings indicated that L-carnitine supplementation was linked to significant improvements in clinical symptoms. Supplementation was associated with significantly improved left ventricular ejection fraction, increased stroke volume and cardiac output, and improved diastolic function. However, no significant effects were seen on all-cause mortality or a 6-minute walk test, a common functional physical performance test for people with moderate to severe cardiovascular disease.

A systematic review and meta-analysis of 13 controlled trials found that L-carnitine supplementation, ranging from 2.7 g/day for 5 days to 6g/day for 12 months between studies in adults with acute myocardial infarction, was associated with reduced all-cause mortality by 27% when compared to placebo. The treatment groups also showed significant reductions in ventricular arrhythmia and the development of angina. No changes in the development of heart failure or myocardial infarction were seen. Furthermore, an association does not indicate direct causality.

While some studies have observed clinical improvement in chronic heart failure patients after supplementing with L-carnitine, according to American and European guidelines, L-carnitine is not recommended as a treatment for heart failure. I would also encourage you to discuss the potential benefits of L-carnitine with your healthcare team if you have heart disease to ensure it does not interfere with any medications or treatment, or cause complications.

Athletic performance

A systematic review of 11 double-blind controlled trials on healthy individuals compared the effects of various forms of L-carnitine on moderate and high-intensity exercise performance. The results showed acute L-carnitine supplementation of 3–4 g 60–90 minutes before exercise improved overall and maximum power. Long-term supplementation for 4–24 weeks with doses of 2–2.74 g of L-carnitine daily also improved athletic performance: increased maximum power and all-out exercise capacity, and lowered perceived exertion. The same benefits were not seen with moderate-intensity exercise.

A randomized, double-blind study on 14 healthy adolescent males found that a carbohydrate solution with 2.0 g of L-carnitine tartrate twice a day for 24 weeks increased muscle activation by 38%, work output by 11%, and reduced muscle lactate, the compound that is produced during exercise and causes muscle soreness, by 44%, compared to baseline. No significant improvements were seen in the carbohydrate solution-only group, despite following the same training regimen and timeline.

A systematic review and meta-analysis of 13 randomized controlled trials looked at the effects of propionyl-L-carnitine (PLC) on exercise performance in individuals with claudication — leg pain during exercise due to the narrowing or blocking of the arteries. The results showed that supplementing with 1 g of PLC twice a day significantly improved peak walking distance compared to placebo.

Several studies suggest that L-carnitine is beneficial for athletic performance, especially peak power and maximum output. However, keep in mind that most studies focused on athletes who already follow an exercise and diet regimen and prioritize recovery. Thus, L-carnitine acts as an additional boost rather than the main driver. Furthermore, no benefits are seen in moderate-intensity exercise, with most fitness enthusiasts falling into this category. So, while L-carnitine has some performance-boosting properties, unless you engage in vigorous exercise or follow a vegan or vegetarian diet, you probably do not need to supplement.

Weight loss

A systematic review and meta-analysis of 37 randomized controlled trials found that supplementing with L-carnitine significantly decreased body weight, body mass index, and fat mass, with no significant changes in waist circumference and body fat percentage. Further analysis revealed that 2,000 mg of L-carnitine daily seems to deliver the maximum benefit for body weight, but no association was established for other metrics.

Another systematic review and meta-analysis of 9 randomized controlled trials found that participants who used L-carnitine lost significantly more weight than the placebo groups.

Some research suggests that L-carnitine supports overall weight loss without significant changes in body fat percentage or waist circumference. However, weight loss is ultimately achieved through a calorie deficit and positive lifestyle changes, making it unlikely to be attributed to any supplement. As the participants of the study go about their lives, the ones taking L-carnitine may adhere to their diets and exercise regimens more. Furthermore, the American Heart Association suggests that waist circumference may be a better indicator of heart health than body weight. Thus, if you want to lose weight for health benefits, L-carnitine is unlikely to be a miracle supplement.

Carnitine supplementation

Carnitine is a widely available dietary supplement and is very popular among fitness enthusiasts, especially those following a vegetarian or vegan diet. The most common forms are powder or capsule.

Recommended dosage

There is no recommended dose or a clearly established tolerable upper intake level. However, doses of more than 3 g a day may cause nausea, vomiting, abdominal cramps, diarrhea, and a fishy body odor.

That being said, if you have been diagnosed with a deficiency and prescribed a fairly high dose of carnitine, you should stick to your doctor’s recommendations. If you think you are experiencing side effects from it, talk to your practitioner about whether it is normal or not; however, do not quit supplementation on your own accord.

Types of supplements

Despite its low bioavailability, L-carnitine is only available as an oral supplement — a capsule, or a powder. As mentioned before, L-carnitine comes in several forms, and naturally, so do the supplements.

• L-carnitine. This form is the most common and affordable, and is used in the majority of studies.
• Acetyl-L-carnitine. This is an acetylated form of L-carnitine, usually used in brain, weight loss, and physical performance studies.
• L-carnitine tartrate. This form is commonly used in exercise performance studies and sold as an exercise supplement.
• Propionyl-L-carnitine. This form is sometimes used in cardiovascular health research studies but is rarely sold as a supplement.

Regardless of the type of L-carnitine supplement you choose, please make sure the product is third-party tested by an independent lab to ensure safety and quality.

Writer’s opinion

I work out a lot, mainly lifting weights, have an active lifestyle, and work in the wellness and supplement field, so naturally, I have tried L-carnitine supplements. I really wanted to experience the performance-boosting and weight-loss-supporting benefits as I was getting back to routine after travel, but honestly, I did not see any improvements despite trying to gaslight myself that I did. This may be because I eat animal products daily and have an occasional energy drink, so I get more than enough carnitine daily. As a scientist, I believe that L-carnitine supplementation may be beneficial for those who do not get enough through their diet to see slight improvements in exercise performance and support weight loss. However, following an exercise plan, meeting your nutrition goals, and having appropriate rest will result in much more significant changes. Regarding cardiovascular health benefits, I think the research is still too scarce and anecdotal to suggest L-carnitine to help with serious conditions like heart failure. You should follow the advice of your healthcare team.

That being said, the research on the benefits of L-carnitine is not conclusive, so you may experience more benefits than I did.

Food sources with L-carnitine

L-carnitine is naturally present in animal foods, with beef being the best source. Below, you will find some animal and plant sources if you want to up your dietary L-carnitine intake.

Animal-based foods

Food	Serving size (cooked)	Carnitine per serving (mg)
Beef	3 oz	42–122
Whole milk	1 cup	8
Cod	3 oz	3–5
Chicken breast	3 oz	2–4
Cheddar cheese	2 oz	2

Plant-based foods

Food	Serving size (cooked)	Carnitine per serving (mg)
Whole wheat bread	2 slices	0.2
Asparagus	1 cup	0.2

Side effects and safety

L-carnitine is generally well-tolerated but can interact with the following medications:

• Pivalate-conjugated antibiotics
• Valproic acid and other anticonvulsants

If you are a child, pregnant or breastfeeding, have diagnosed conditions, or are taking prescription medication, you should consult your doctor to ensure safety.

Side effects of L-carnitine supplementation

Although generally safe, carnitine may cause some side effects, especially if taken in large doses (more than 3 g daily):

Who can benefit from L-carnitine supplements?

Most healthy people get enough L-carnitine without much thought, but some groups may benefit from supplementation.

Athletes and bodybuilders

L-carnitine is popular in the fitness industry for a reason. The compound has been shown to increase peak power and work output, as outlined above. Athletes and bodybuilders may opt to supplement to get this extra boost.

Also, one study showed that L-carnitine reduces lactate, a compound that causes sore muscles. While excessive soreness signifies the need to rest and recover for an average person who works out, professionals sometimes need to push through and reduce the soreness as much as possible due to strenuous demands and the pressure to perform.

Vegetarians and vegans

As seen in the section on food sources with L-carnitine, animal products are rich in L-carnitine, while plant sources are pretty scarce. Whole wheat products and asparagus are the main sources, and they have only a fraction of what animal products provide. Thus, those following a vegetarian or vegan diet may want to supplement with L-carnitine.

Bottom line

L-carnitine is a fairly common supplement, especially in the fitness industry, due to its potential exercise performance-boosting and weight loss benefits. The research is pretty solid for both of these benefits, especially if you engage in high-intensity exercise. However, I would highlight that supplements are only a cherry on top of a healthy lifestyle and good habits.

While most healthy individuals get enough carnitine through their diet, some people have primary or secondary deficiencies that require taking a prescribed dose and frequent health monitoring. Also, those following a vegan or vegetarian diet may fall short of the daily requirements, as plant products have only negligible amounts of carnitine.

Regarding cardiovascular health benefits, I did find supporting evidence, however, any cardiovascular condition should be monitored by your healthcare team, with which you could discuss L-carnitine supplements.

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Further reading

AKG Supplement: Benefits, How It Works, and Potential Side Effects

Can Probiotics Help Lower High Blood Pressure?

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