L-Carnitine is considered one of the most controversial sports supplements in sports nutrition.
Advertising slogans emphasize its amazing properties as a fat burner, which “all fitness enthusiasts use for weight loss,” while sellers of sports nutrition add to this the benefits for muscle gain, increased energy, and endurance; some even talk about carnitine’s ability to improve sexual function.
The internet is filled with enthusiastic reviews of its effectiveness for weight loss… And only skeptical scientists critically examine almost all the listed properties of L-carnitine.
Below we will discuss what L-carnitine is, what it is needed for in sports and medicine, analyze its properties, look at what dangers and for whom its deficiency in the diet poses, and whether athletes are at risk of deficiency.
What is L-carnitine?
L-carnitine appeared on the sports nutrition market as a weight loss supplement in the 1980s. It was then overshadowed by significantly more effective fat burners of the next generation containing stimulants, hormones, and anabolic steroids.
In our time, as one of the authors of a popular Western online sports nutrition store puts it, “… there has been a kind of resurrection of L-carnitine… it has returned and become stronger than ever; only now not just as a fat burner, but also as a supplement that increases physical performance and aids recovery…”
Let’s take a look at what lies behind these lofty words.
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L-carnitine is a natural substance that plays an important role in human metabolism.
In sports, L-carnitine refers to a type of sports nutrition that is used as a fat burner for weight loss, as well as a supplement to stimulate muscle growth and energy.
Carnitine is found in almost every cell of the body. Its name comes from the Latin carnus (“flesh”), as it was first obtained from animal meat. It is found in high concentrations in muscles (including the heart), the brain, and even in sperm.
In terms of its properties, it is similar to vitamins (primarily those of group B) and amino acids, as it is just as important for the body. Emphasizing this important role, in the 1950s scientists referred to it as “vitamin BT.”
However, it is not a vitamin or mineral, which, by definition, must be obtained from food to avoid deficiency states and related disorders or diseases.
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How L-carnitine Works
L-carnitine plays an important role in energy production from fats in the body. It does this by transporting fat into the cells, into the mitochondria, which are like mini-engines: they burn fats and produce energy 5,7,20.
It is from this property of carnitine that the popularity of its use as a fat burner “grows.”
Carnitine can be synthesized in the body from two essential amino acids, lysine and methionine 2. For this, a sufficient amount of vitamin C 21 is necessary.
In small amounts, L-carnitine is obtained from animal-derived foods (fish and meat) 22.
Vegans, some types of vegetarians, and people with certain genetic disorders are at risk of deficiency, as their bodies either do not produce carnitine at all or produce it in very small amounts.
For this reason, L-carnitine is sometimes referred to as a “conditionally essential” substance 4.
L-carnitine is a natural substance that performs important metabolic functions in the body; in sports, it is a type of sports nutrition used for weight loss, muscle growth, and energy.
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In which products is L-carnitine found?
The sources of carnitine that enter the body are primarily animal products.
It is found in large quantities in meat (the redder it is, the more), in smaller amounts in milk (mainly in whey) 1, and in significantly smaller amounts in plant products, such as avocados and soybeans.
Carnitine is also present in human breast milk.
Animal products contain significantly more carnitine than plant products. And the redder the meat, the higher its concentration.
The National Institutes of Health in the USA recommends the following carnitine-rich foods 16:
| Carnitine in food products | ||
|---|---|---|
| Product | Serving | Carnitine content, mg |
| Beef (lean), cooked | 1 serving (112 g) | 56-162 |
| Ground beef, cooked | 1 serving (112 g) | 87-99 |
| Whole milk | 1 cup | 8 |
| Cod, cooked | 1 serving (112 g) | 3-5 |
| Chicken breast, cooked | 1 serving (112 g) | 3-5 |
| Ice cream | 1/2 cup | 3 |
| Cheddar cheese | 1 serving (56 g) | 2 |
| Whole grain bread | 2 slices | 0.2 |
| Asparagus, cooked | 1/2 cup | 0.1 |
Carnitine from natural products is better absorbed: by 57-84%, while in supplement form, it is only 14-18% 3. The dose size likely matters: at smaller doses, absorption is more complete.
On average, non-vegetarians consume about 2-12 mcg of carnitine per kilogram of body weight per day, while vegetarians consume significantly less 4,5. For an omnivorous person weighing ~100 kg, this amounts to about 1 mg daily.
The dose of carnitine in special supplements is thousands of times higher: 1-4 grams. At this dosage, even with low absorption, about 250-500 mg remains in the body, which is significantly more than from meat products.
Carnitine from natural products is absorbed significantly better than from supplements; however, its concentration in supplements is 1000 times higher.
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What is L-carnitine for? Useful properties
Most of those who are familiar with L-carnitine and take it do so with the sole purpose of losing weight. Carnitine is one of the most popular fat burners.
The basis for such use is indeed present and it lies in the main property of L-carnitine: it participates in the production of energy from fats 20,26,27. Carnitine helps transport fats into the cells’ mitochondria, where they are “burned” for energy.
All other beneficial functions of carnitine and the reasons for its usual intake are related to this property. Let’s summarize them:
- fat burning (weight loss);
- muscle mass gain and increase in muscle strength;
- increased athletic performance (increased endurance, reduced fatigue);
- removal of toxic compounds from the byproducts of fat cell burning, preventing their accumulation;
- stimulation of brain activity, increased alertness and mitochondrial potential, ensuring the health of nerve cells;
- softening of the side effects of aging;
- combating depression and chronic fatigue;
- improving sexual health;
- improving vascular health;
- protection of nerve cells and their recovery after damage due to diabetes and diabetic neuropathy.
The list is impressive and leaves no doubt about the benefits of taking this supplement… But one should not rush, as scientific research does not confirm all of the listed properties.
Approximately 98% of all L-carnitine in the body is stored in the muscles (the remaining portion is in the liver and blood) 28, which clearly indicates its important role in their functioning.
L-carnitine supports mitochondrial function, thus protecting the body from aging and the development of related age-related diseases 29.
Recent studies confirm that L-carnitine is beneficial for heart and brain health 30,31.
L-carnitine has many beneficial properties, but the most important ones for which it is usually taken (weight loss and muscle mass gain) are questioned by scientists. The opinions of scientists and sports nutrition sellers regarding the purpose of L-carnitine significantly diverge.
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The benefits of L-carnitine for weight loss
In the world of sports, L-carnitine is widely advertised as an effective fat burner, and as confirmation, sellers always refer to its main property: the transport of fat into cells for burning and energy production.
The logic behind its sale as a dietary supplement is very simple: the more we consume, the better fats are burned… The principle is straightforward, logical, but in the world of dietary supplements and sports nutrition in particular, it does not always work.
Opinions among scientists and sellers regarding the benefits of L-carnitine for weight loss differ significantly.
For scientists and researchers, unlike sellers and marketers, it is more typical to speak merely about the theoretical ability of L-carnitine to enhance fat burning.
In practice, as studies show, it is useless for this purpose.
Researchers at the portal Examine.com, whose mission is to provide an objective scientific perspective on the benefits and effectiveness of various supplements, state that “numerous studies on the benefits of L-carnitine for weight loss are very contradictory and generally refute its effectiveness“. See our study on the benefits of L-carnitine for weight loss.
Most often, the effect of fat burning is explained by scientists as a simple increase in physical activity, due to the intake of a greater number of calories from L-carnitine or products containing it.
Scientific studies of L-carnitine as a fat burner are very contradictory and generally refute its effectiveness
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The Benefits of L-Carnitine in Sports
As for the benefits of L-carnitine for gaining muscle mass, increasing endurance, and improving other performance indicators in sports – another “beneficial” property for which it is taken – scientists also question this.
Scientific research on this issue is also very contradictory. Some studies demonstrate a slight effect when taking L-carnitine in very large doses or over a long period, while others speak of its complete uselessness.
As one possible reason for such contradictions, the “delayed” action of carnitine is sometimes mentioned: its effect does not manifest immediately after intake, as with energy drinks containing caffeine, for example, but rather weeks or even months after starting intake, which complicates the establishment of a causal relationship.
The uncompromising conclusion of the researchers at Examine.com:
“20 years of research on L-carnitine do not confirm its effectiveness in increasing muscle strength or mass, endurance, or recovery speed, and there is no scientific justification for its additional use by athletes.”
Learn more about the benefits, or rather – the uselessness of L-carnitine in sports for gaining muscle mass, increasing muscle strength, and endurance in our study on the benefits of L-carnitine in sports and bodybuilding.
20 years of research do not confirm the benefits of L-carnitine in sports for increasing muscle mass, strength, or other indicators
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The benefits of L-carnitine for the heart
Some studies demonstrate the property of carnitine to lower blood pressure, as well as its anti-inflammatory effect in certain heart diseases 31,33.
In one of them, participants took 2 grams of acetyl-L-carnitine per day. As a result, blood pressure decreased, and the concentration of substances used to assess heart health and disease risk decreased by tens of times 31.
There is also evidence that the intake of L-carnitine improves the condition of patients with serious heart diseases, particularly coronary artery disease and chronic heart failure 34-36.
The benefits of L-carnitine for the brain
L-carnitine has clear advantages for brain function.
Animal studies show that acetyl-L-carnitine is effective in preventing age-related cognitive decline 39.
Taking acetyl-L-carnitine by elderly individuals helps halt the progression of Alzheimer’s disease and other brain disorders 40,41.
Scientific research also confirms that the intake of L-carnitine is beneficial for all elderly people, including those who do not suffer from Alzheimer’s disease 42,43.
L-carnitine has a protective function for brain cells and protects them from damage. In one study, when alcoholics took 2 grams of acetyl-L-carnitine for 90 days, significant improvements in various cognitive performance indicators were observed 44.
L-carnitine in the form of acetyl-L-carnitine is beneficial for brain health and protects its cells from damage
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Who needs L-carnitine as a supplement: at-risk groups for its deficiency
The deficiency of carnitine can be observed in some categories of people due to insufficient intake from food or when the mechanism of its absorption and synthesis in the body is impaired.
The lack of carnitine is especially dangerous for the heart muscle due to its high energy demands.
1 Veganism and Vegetarianism
Vegetarians and vegans are the first at risk of carnitine deficiency, as their diet does not contain animal products 5 – the main natural source of L-carnitine.
They can be recommended additional intake of carnitine in the form of supplements. Research indicates that when carnitine enters their bodies, it is absorbed very effectively 5, however, it is poorly transported to the muscles 6.
Overall, despite the obviousness of the problem, there is very little research on the benefits of additional carnitine intake for vegetarians.
Vegetarians and vegans are at risk of carnitine deficiency due to the absence of animal products in their diet.
2 Athletes
As for athletes, contrary to popular belief, scientists say that they are not at risk of carnitine deficiency and do not need additional intake 17.
In conjunction with the fact that its effectiveness for fat burning and increasing endurance is unproven, the rationale for its additional intake in sports is questionable.
Athletes are not at risk of carnitine deficiency and do not need additional intake.
3 Medications and Carnitine Deficiency
Some medications can interfere with the absorption of carnitine and lead to its deficiency.
For instance, the heart medication Mildronate reduces the level of L-carnitine by 18% by the 4th week of intake and with long-term use contributes to the development of its deficiency 6.
4 Diseases Associated with Carnitine Deficiency
Chronic deficiency of L-carnitine can lead to the following conditions:
- dementia 8;
- muscle weakness and liver dysfunction 9;
- cardiomyopathy (heart muscle disease) 10;
- hypoglycemia (low blood glucose).
Increased doses of carnitine are used to treat these and other diseases in medicine.
5 L-Carnitine and Cancer
The deficiency of carnitine can be observed in certain cancers, which is why it is being studied as an adjunct treatment for cancer.
In one study, a gradual increase in doses of carnitine (0.5 g over 2 days, 1 g over 2 days, 2 g over 10 days) taken by patients with progressive cancer and carnitine deficiency led to a reduction in fatigue, improvement in overall well-being, and a decrease in the degree of functional impairments related to cancer.
There was also a significant increase in muscle mass and appetite. For this category, doses of carnitine up to 3000 mg per day have been shown to be safe 11-15.
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Conclusion
The most common answer to the question of what L-carnitine is and what it is needed for is “it’s a fat burner” and it is useful for weight loss. Scientific research does not support this.
Most studies demonstrate the beneficial properties of L-carnitine as a supplement for improving brain, heart, and vascular health.
Athletes are not at risk of carnitine deficiency and do not need additional intake. But even when they do, athletic performance does not significantly improve.
The intake of L-carnitine as a supplement may be recommended for elderly people and vegans/vegetarians, as well as in certain diseases.
Of all forms, acetyl-L-carnitine and L-carnitine are the most effective.
