L-carnitine

L-carnitine is a popular supplement in the fitness and weight loss worlds due to its potential to improve fat metabolism and promote weight loss. However, it is important to understand how exactly L-carnitine may impact weight loss and what evidence supports its effectiveness.

[ 1 ], [ 2 ], [ 3 ]

How does L-Carnitine work?

L-carnitine is a naturally occurring substance related to B vitamins that plays an important role in the body’s process of converting fat into energy. It transports long-chain fatty acids into the mitochondria of cells, where fats are oxidized and converted into energy. This makes L-carnitine attractive to those seeking to lose weight, as it is thought to increase the amount of fat burned and improve exercise endurance.

L-carnitine is synthesized in the body from the amino acids lysine and methionine. It is found in animal foods (meat, dairy products) and, to a much lesser extent, plant foods. It is a short-chain carboxylic acid containing nitrogen. About 90% of carnitine entering the body is found in muscle tissue. Theoretically, carnitine supplements can increase fatty acid oxidation by facilitating the transport of long-chain fatty acids into the mitochondria. L-carnitine can also facilitate the oxidation of pyruvate, which increases glucose utilization and reduces lactic acid formation during exercise.

Main functions

• Increases the utilization of fatty acids as an energy source.
• Reduces the amount of fat in the body.
• Increases endurance.

Research on the effectiveness of L-carnitine

Despite L-carnitine’s popularity as a weight loss aid, scientific evidence for its effectiveness remains mixed. Some studies have shown modest improvements in weight loss and endurance among participants who regularly take L-carnitine supplements, while other studies have found no significant difference in weight loss between L-carnitine and control groups.

Why does the body need L-carnitine?

L-carnitine is a B-vitamin-related substance naturally produced in the human body. It plays a key role in energy metabolism by transporting fatty acids into the mitochondria, the cell organelles where these acids are oxidized and converted into energy. Here are the main functions and benefits of L-carnitine for the body:

1. Improved Energy Metabolism: L-Carnitine promotes more efficient use of fat as an energy source, which can help increase endurance and reduce fatigue.
2. Cardiovascular Support: Research shows that L-carnitine may have positive effects on the cardiovascular system, improving heart function and reducing the risk of developing certain diseases.
3. Aid in weight loss: While L-carnitine alone is not a “magic pill” for weight loss, it may help you burn fat more effectively, especially when combined with a healthy diet and regular exercise.
4. Supports exercise recovery: L-carnitine may reduce muscle soreness and promote faster muscle recovery after intense exercise.
5. Increased Metabolic Efficiency: L-Carnitine helps optimize metabolic processes, improving metabolism and promoting more efficient use of nutrients.
6. Neuroprotective effect: There is evidence that L-carnitine has a protective effect on the nervous system and may have a positive effect in some neurodegenerative diseases.

However, despite the many potential benefits, L-carnitine supplements should be used with caution and under the supervision of a physician, especially if you have a medical condition or are taking other medications.

Benefits of L-Carnitine

L-carnitine is a conditionally essential nutrient that plays an important role in energy production and fatty acid metabolism. Several studies point to various potential benefits of supplementing L-carnitine in the diet:

1. Improved recovery after exercise: L-carnitine may reduce muscle damage and decrease markers of cellular damage and free radical formation, as well as alleviate muscle soreness. Supplementing with L-carnitine may improve blood flow and oxygen delivery to muscle tissue, reducing hypoxic stress and promoting recovery after exercise ( Fielding et al., 2018 ).
2. Metabolic functions and importance in humans: L-carnitine is involved in the transport of fatty acid chains into the mitochondrial matrix, allowing cells to break down fats and obtain energy from fat stores. It may have antioxidant properties, suggesting it as a treatment for many conditions, including heart failure, angina, and weight loss ( Pękala et al., 2011 ).
3. Protection of plasma components from oxidative changes: L-carnitine added to blood plasma in vitro studies protected plasma proteins and lipids from oxidation and nitration caused by peroxynitrite, a strong oxidizing/nitrating agent. This indicates a potential antioxidant activity of L-carnitine (Kołodziejczyk et al., 2011).
4. Sports Uses: Although evidence for L-carnitine's effects on improving endurance and athletic performance is mixed, some studies suggest its potential benefit in improving fat utilization as an energy source, which may contribute to increased exercise endurance ( Karlic & Lohninger, 2004 ).

It is important to note that despite the potential benefits, the effects of L-carnitine may vary depending on the individual and the specific conditions in which it is used. It is also recommended that you consult with your doctor before taking L-carnitine as a supplement, especially if you have a medical condition or are taking other medications.

L-carnitine supplements

L-carnitine preparations are widely available on the market as dietary supplements and medical products. They can be used to improve fatty acid metabolism, increase endurance, improve recovery after intense physical activity, and in the complex treatment of cardiovascular and neurological diseases. Here are some examples of preparations and supplements containing L-carnitine:

1. L-Carnitine Fumarate - Often used in sports supplements to improve endurance and promote fat burning.
2. Acetyl-L-Carnitine is a form of L-carnitine that is better absorbed and penetrates the blood-brain barrier, making it useful for supporting brain function, including memory and attention.
3. Propionyl-L-carnitine - This form is often studied in the context of improving blood circulation and treating chronic heart failure.
4. L-Carnitine Tartrate is one of the most common forms of L-Carnitine in sports supplements, known for its high bioavailability.

L-carnitine supplements and preparations are available in a variety of forms, including capsules, tablets, liquids, and powders. It is important to note that the effectiveness and safety of L-carnitine supplements may depend on many factors, including individual factors, medical conditions, and other medications. Before starting to take L-carnitine or its analogues, it is recommended to consult with a physician or qualified healthcare professional to determine the most appropriate form, dosage, and possible interactions with other medications.

How to take L-carnitine?

Dosages of L-carnitine for weight loss have varied in studies, but are typically in the range of 500 mg to 2,000 mg per day, taken with food for best absorption. It is important to start at the lower end of this range to assess tolerance and gradually increase the dose if needed.

When is the best time to take L-carnitine?

The timing of your L-carnitine intake can impact its effectiveness, especially if your goal is weight loss or improving athletic performance. Let's look at the optimal timing for taking L-carnitine based on different goals:

1. To improve physical endurance and athletic performance

• Before exercise: Take L-carnitine 30-60 minutes before exercise. This can increase endurance, improve fat metabolism, and reduce fatigue because L-carnitine helps the body use fat more efficiently as an energy source during exercise.

2. For weight loss

• Before Meals: If your primary goal is weight loss, consider taking L-carnitine 15-30 minutes before major meals or physical activity. This may help improve fat oxidation.

3. For general improvement of metabolism

• In the morning: Taking L-carnitine in the morning on an empty stomach can help boost your metabolism throughout the day. It can also help you use fat for energy more efficiently.

4. During the day

• Between Meals: This can help maintain metabolism and energy balance, especially between meals when energy levels may be low.

General recommendations

• Not Before Bed: Avoid taking L-carnitine immediately before bed, as its energizing effects may interfere with sleep quality.

Additional tips

• Co-administration with carbohydrates: Some studies suggest that taking L-carnitine in combination with carbohydrates may improve its absorption and increase muscle carnitine levels, which could potentially improve athletic performance and support weight loss.
• Consult with your doctor: Before taking L-carnitine, especially if you have a medical condition or are taking medications, you should consult with your doctor.

The timing of your L-carnitine intake should be based on your individual goals and lifestyle. Some people may see better results when taking it before workouts, while others may benefit from taking it in the morning or between meals to support metabolism.

L-Carnitine Side Effects

Taking L-carnitine may cause some side effects, although it is considered safe and well-tolerated in many cases. Here are some of the side effects and downsides associated with taking L-carnitine that have been mentioned in studies:

1. Digestive and circulatory problems: L-carnitine can cause side effects, the most common of which are digestive problems and circulatory abnormalities. In some cases, L-carnitine can affect the user’s mental state.
2. Liver and Kidney Impairment with Long-Term Use: A study in rats showed that long-term use of L-carnitine may negatively affect liver and kidney function by causing oxidative stress and activation of the inflammatory process in the liver, as well as potentially impairing kidney function.
3. Effects on the Gut Microbiome and Liver Function: High L-carnitine intake may disrupt the composition of the gut microbiome, causing a buildup of harmful bacteria and negatively impacting liver function, leading to increased levels of certain inflammatory markers and metabolites associated with liver function decline.

It is important to note that many studies highlight the potential benefits of L-carnitine for a variety of medical conditions, including cardiovascular disease and conditions related to energy metabolism. However, more research is needed to confirm the safety of long-term use of L-carnitine, especially at high doses. It is recommended to consult with your doctor before starting L-carnitine supplementation, especially if you have a chronic medical condition or are taking other medications.

Contraindications of L-carnitine

No studies specifically focusing on contraindications for L-carnitine were found in the available literature. However, based on the available data, L-carnitine is generally considered safe to take at recommended doses for most people. However, there are certain situations and conditions in which L-carnitine consumption may require caution or may not be recommended:

1. Pregnancy and breastfeeding: There is limited safety data on L-carnitine during pregnancy and breastfeeding, so women during these periods are advised to avoid its use without consulting a doctor.
2. Allergy or Intolerance: People with a known allergy or sensitivity to L-Carnitine or its components should avoid taking it.
3. People with certain medical conditions: People with certain conditions, such as liver or kidney disease, may need to adjust their L-carnitine dosage or avoid it altogether. Caution should also be exercised if you have certain metabolic disorders.
4. Drug interactions: L-carnitine may interact with some types of medications, including those used to treat thyroid disease. Therefore, it is important to consult with your doctor before taking L-carnitine, especially if you are taking other medications.

In general, L-carnitine is considered safe for most people when taken at recommended doses. However, if you have certain medical conditions or are taking other medications, you should consult with a healthcare professional before taking L-carnitine.

L-Carnitine Overdose

L-carnitine overdose is rare, but it can occur when taking excessively high doses of the substance, especially in the form of dietary supplements. The human body usually tolerates L-carnitine well, and excess is usually excreted by the kidneys. However, if the recommended doses are significantly exceeded, some unwanted effects may occur.

Symptoms of an L-carnitine overdose may include:

• Nausea and vomiting
• Diarrhea
• Stomach ache
• Muscle weakness
• Bad breath (fishy odor), sweat, and urine due to accumulation of trimethylamine, a metabolic product of L-carnitine
• Insomnia or increased excitability
• Arrhythmia or other changes in heart rhythm (in very rare cases)

What to do if you suspect an overdose:

1. Discontinue Use: If you suspect an L-carnitine overdose, discontinue use immediately.
2. Seek medical attention: If symptoms are severe or if the condition is causing concern, you should immediately contact your doctor or go to the nearest hospital.
3. Maintain Hydration: If you have symptoms such as vomiting and diarrhea, it is important to stay hydrated by drinking enough water.

Overdose prevention:

• Following Recommended Dosages: Always follow the dosage recommendations on the supplement package or as directed by your healthcare professional.
• Consult with your doctor: Before taking L-carnitine, especially if you have a chronic medical condition or are taking other medications, consult with your doctor.
• Caution When Using High Doses: Avoid exceeding the recommended doses, even if you do not experience immediate improvement in your conditions or achieve the desired fitness results.

L-carnitine may be a useful substance for supporting metabolism and improving physical performance when used in moderation and in a controlled manner. However, it is important to be aware of the potential risks of overdose and to adhere to safe use practices.

L-carnitine during pregnancy

Research on the use of L-carnitine during pregnancy points to its important role and potential positive effects:

1. The study by Bai et al. (2019) discussed that the plasma L-carnitine level in pregnant women was significantly reduced, but this did not result in a decrease in maternal liver fatty acid beta-oxidation. It is suggested that the transfer of L-carnitine across the placenta plays a key role in reducing the plasma L-carnitine level in pregnant women, which did not result in a decrease in maternal liver fatty acid oxidation ( Bai et al., 2019 ).
2. A study by De Bruyn et al. (2015) presented cases of carnitine deficiency in pregnant women, highlighting the importance of L-carnitine supplementation during pregnancy. Carnitine supplementation is recommended to prevent serious complications associated with its deficiency and should be continued throughout pregnancy according to plasma concentrations ( De Bruyn et al., 2015 ).

These studies highlight the important role of L-carnitine in supporting energy metabolism and the potential need for supplementation during pregnancy to support maternal and fetal health. However, pregnant women should consult with their physician before starting L-carnitine or its analogues to ensure that such supplementation is safe and appropriate for their individual needs.

L-carnitine for children

Research on L-carnitine use in children highlights its potential benefits, but also suggests the need for further research and caution when using it. Here are some key findings from the available research:

1. Safety and Efficacy: Some studies suggest the safety and potential benefits of L-carnitine for certain conditions in children, but emphasize the need for an individual approach and monitoring by healthcare professionals.
2. Treatment and prevention: L-carnitine is being explored as a treatment and prevention option for a variety of conditions, including metabolic disorders and cardiovascular disease, but the importance of additional research to confirm its effectiveness is emphasized.
3. Metabolic Disorders: Some studies discuss the role of L-carnitine in improving metabolic function in children with certain disorders, indicating potential benefits when used appropriately.
4. Dosage and Administration: Reviews emphasize the importance of accurate dosing and monitoring when using L-carnitine in children, noting the risk of possible side effects if used incorrectly.
5. Need for more research: Almost all studies indicate the need for further clinical trials to better understand the effects of L-carnitine on children and to develop recommendations for its use.

Overall, the existing data highlight the potential of L-carnitine as a supplement to improve health and treat certain conditions in children, but also highlight the need for caution, careful monitoring, and additional research to determine optimal dosages and regimens. It is important for parents and caregivers to consult with a healthcare professional before introducing L-carnitine to children.

Research results

Results from studies of L-carnitine supplementation do not demonstrate an ergogenic effect. Trappe et al. evaluated the effects of L-carnitine supplementation in swimmers to determine whether L-carnitine would improve performance by reducing lactic acid accumulation. Subjects were 20 male collegiate swimmers who had trained for 16 weeks prior to the experiment.

Subjects performed 5 repetitions of a 100-yard distance with a 2-minute recovery period between swims before and after one week of L-carnitine supplementation. The supplementation group received 236 ml of a citrus drink containing 4 g of L-carnitine in the morning and evening. The placebo group received the same amount of citrus drink but without L-carnitine. In the final swim, no differences were found between the two groups in lactic acid, blood pH, or swimming speed, indicating that L-carnitine supplementation does not improve performance.

Greig et al. looked at the effects of L-carnitine supplementation on maximal and submaximal exercise capacity. In two separate tests, two groups of untrained individuals were given either 2 g L-carnitine per day or placebo for two weeks. Exercise capacity was assessed using continuous ergometry. A small improvement in submaximal performance at 50% V02max was found in the L-carnitine test. However, HR was nonsignificantly lower at all exercise intensities during maximal exercise in the L-carnitine group. The researchers concluded that L-carnitine supplementation provided little or no improvement.

L-carnitine in foods

L-carnitine is a B-vitamin-related substance that plays a key role in energy production by transporting fatty acids into the mitochondria of cells, where they are oxidized and converted into energy. Although the body can produce enough L-carnitine, it is also found in some foods, especially meat and other animal products. Here is a list of foods with the highest L-carnitine content:

Meat products:

• Red meat: Beef and lamb are among the best sources of L-carnitine. For example, steak can contain up to 95 mg of L-carnitine per 100 g of product.
• Pork: Also contains significant amounts of L-carnitine, although less than red meat.

Dairy products:

• Milk: Whole milk in particular is a good source of L-carnitine.
• Cheese: Some types of cheese also contain L-carnitine, but in smaller quantities than meat.

Fish and seafood:

• Fish: Fatty fish, such as salmon, are especially high in L-carnitine.
• Seafood: Shrimp and other seafood can also be sources of L-carnitine.

Bird:

• Chicken and turkey: Contain L-carnitine, but in smaller amounts than red meat.

Vegetarian sources:

Although L-carnitine is found primarily in animal products, small amounts can also be found in some plant foods, such as:

• Avocado
• Nuts
• Some legumes

However, vegetarians may have a harder time getting enough L-carnitine from plant foods alone and may want to consider taking supplements after consulting with a doctor.

It is important to note that for most healthy people, the body produces enough L-carnitine to meet its needs, and supplementation is only needed under certain medical conditions or with special dietary regimens, such as strict vegetarianism or veganism.

L-carnitine analogues

Studies directly examining L-carnitine analogues and their potential effects similar to L-carnitine are limited in the available literature. However, when examining the role and mechanism of action of L-carnitine, it is possible to consider several substances and approaches that may have similar metabolic effects:

1. Acetyl-L-carnitine: A derivative of L-carnitine, it has similar properties but may also have additional neuroprotective effects. Acetyl-L-carnitine more easily crosses the blood-brain barrier, making it a preferred choice for the treatment of neurological disorders (Kelly, 1998).
2. Propionyl-L-Carnitine: This L-carnitine analogue has specific properties that may be useful in the treatment of cardiovascular disease, including improving endothelial function and reducing symptoms of peripheral arterial disease.
3. Coenzyme Q10: Although not a direct analog of L-carnitine, Coenzyme Q10 plays a key role in mitochondrial energy metabolism and may be used to support cardiac function and improve endurance.
4. Omega-3 fatty acids: Have different mechanisms of action, but may help improve fatty acid metabolism and have cardioprotective effects similar to L-carnitine.
5. B vitamins: Essential for energy metabolism and may complement the action of L-carnitine by helping convert food into energy.

Given the variety of potential analogues and supplements, it is important to emphasize that the choice of a specific substance or combination should be based on specific treatment goals, individual tolerance, and specialist recommendations. Consulting a doctor before starting any supplement is especially important to achieve the best results and minimize the risk of unwanted effects.

Important Considerations

• L-carnitine is generally considered safe for most people when taken at recommended doses, but side effects such as nausea, vomiting, upset stomach, and diarrhea are possible.
• The effectiveness of L-carnitine for weight loss may depend on individual factors, including diet, activity level, and overall health.
• Supplementing L-carnitine intake with a healthy diet and regular exercise may enhance its potential weight loss benefits.

Conclusion

Although L-carnitine may help with weight loss and physical performance, it should not be considered a miracle cure. A balanced diet and regular exercise remain key components of successful weight loss. It is recommended to consult with your doctor before taking L-carnitine or any other supplements.

List of studies related to the study of L-carnitine

1. " Supplementation of L- carnitine in athletes: does it make sense? " - A study conducted by a group of authors led by Fatouros IG was published in the journal Med Sci Sports Exerc in October 2010. The study examines the advisability of supplementing athletes' diets with L-carnitine.
2. " Effect of L-carnitine and/or L-acetyl-carnitine in nutritional treatment for male infertility: a systematic review " - This systematic review on the effect of L-carnitine and/or L-acetylcarnitine in the treatment of male infertility was published in the DARE database. The review analyzed the results of nine RCTs with a total of 862 participants.
3. " L-Carnitine - Metabolic Functions and Meaning in Humans Life " - An article by Jolanta Pekala et al. published in Current Drug Metabolism, Issue 7, Volume 12, examines the metabolic functions of L-carnitine and its meaning in human life. The study examines both the dietary sources of L-carnitine, its role in fat metabolism, and its impact on various diseases.
4. " New perspectives on nutritional interventions to augment lipid utilisation during exercise." - Gonzalez JT, Stevenson EJ, published in Br J Nutr in February 2012.
5. " Carnitine and sports medicine: use or abuse? " - Brass EP, published in Ann NY Acad Sci in November 2004.
6. " L-Carnitine and Male Fertility: Is Supplementation Beneficial? " - Mateus FG, Moreira S, Martins AD, Oliveira PF, Alves MG, Pereira ML, published in J Clin Med on September 6, 2023.
7. "Targeted Metabolomics in High Performance Sports: Differences between the Resting Metabolic Profile of Endurance- and Strength-Trained Athletes in Comparison with Sedentary Subjects over the Course of a Training Year of a Training Year." - Parstorfer M, Poschet G, Kronsteiner D, Brüning K, Friedmann-Bette B., published in Metabolites July 10, 2023.
8. " Effects of L-Carnitine Intake on Exercise-Induced Muscle Damage and Oxidative Stress: A Narrative Scoping Review." - Caballero-García A, Norie, published without date.
9. " Effect of L-carnitine and/or L-acetyl-carnitine in nutritional treatment for male infertility: a systematic review ", published in the DARE database, includes an analysis of nine randomized controlled trials (RCTs) with a total of 862 participants.
10. " L-Carnitine - Metabolic Functions and Meaning in Humans Life ", authors: Jolanta Pekala, Bozena Patkowska-Sokola, Robert Bodkowski, Dorota Jamroz, Piotr Nowakowski, Stanislaw Lochynski, Tadeusz Librowski, published in the journal Current Drug Metabolism.