L-Carnitine is a amino acid derivative involved in energy metabolism and fat transport. It's used as a supplement to help you burn fat... but Can L-Carnitine help you to burn fat?
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What’s L-Carnitine?
L-Carnitine is a quaternary amine, synthesized from lysine and methionine.
Its main action in the metabolism is to transport fatty acids to the mitochondria (study), where fat oxidation occurs.
You can obtain L-Carnitine through:
- Supplementation: different formulas of L-Carnitine provide exogenous L-Carnitine
- Dietary sources: foods like meats or fish naturally contain L-Carnitine
- Dietary amino acids: intakes of lysine and methionine will be used to form L-Carnitine
How Does L-Carnitine Work?
L-Carnitine transports fatty acids to the mitochondria, being involved in fat metabolism (study).
Once Acyl-CoA has passed the outer mitochondrial membrane, CoA is replaced by Carnitine by the enzyme CPT1, forming Acyl-carnitine.
Acyl-Carnitine can now pass through the inner membrane by CAT. Once inside the mitochondrial matrix, carnitine is replaced by CoA to synthesize back Acyl-CoA.
Carnitine will then pass back to the intermembrane space, and everything is repetead. Acyl-Co will be converted to Acetyl-CoA to start the TCA cycle (study)
In other words, L-Carnitine acts as a policeman controlling mitochondrial homeostasis and preventing accumulation of undesired compounds.
L-Carnitine has a protective effect on mitochondrial function, enhancing both directly and indirectly fat transport an oxidation (study)
L-Carnitine to Burn Fat
L-Carnitine is known to be a fat burner, enhancing fat oxidation and consequent fat loss.
Scientific Evidence
Studies show controversial results regarding he use of L-Carnitine to burn fat.
Some studies show how supplementing with L-Carnitine doesn't translate into an increase of muscle carnitine (study).
This other study didn't show any significant effect on metabolic adaptations during HIIT training (study).
L-Carnitine does show some positive sides, too.
In obese subjects, it increases fat oxidation (study). Subjects with L-Carnitine deficiency also benefit from L-Carnitine supplementation. It increases fat oxidation and modulates energy metabolism (study)
Recent studies suggest an increase in muscle carnitine when co-ingested for long periods with carbohydrates (study)(study).
Can L-Carnitine be used to burn fat?
Acute ingestion of L-Carnitine on healthy and physically active subjects doesn't seem to have an effect on fat oxidation.
However, obese or deficient on L-Carnitine subjects could benefit from L-Carnitine supplementation.
Chronic co-ingestion with carbohydrates show an increase on fat utilization and shift on energy metabolism.
Insulin stimulates carnitine transport into the muscle, increasing carnitine levels and enhancing fat oxidation (study).
However, 80g carbohydrates are needed to elevate carnitine levels in the muscle. This big amounts could be a problem for some people.
Why Doesn’t L-Carnitine Work?
L-Carnitine is Not the Limiting Factor
L-Carnitine is needed for fat transport, but it's not the limiting factor. The enymes modulating this process (CPT I and CAT) are, in fact, the limiting factors.
If the enzymes are not able to handle more carnitine, the reaction would remain unchanged (study).
If carnitine levels go beyond Vmax, the reaction rate will not further increase, remaining uchanged.
Increasing L-Carnitine levels doesn't increase fat transport and oxidation.
L-Carnitine is not Essential
L-Carnitine is not essential. You can synthesize it from Lysine and Methionine (study).
Food can not only provide amino acids to indirectly increase L-Carnitine, but some also contain L-Carnitine.
The foods with highest content of L-Carnitine are red meat, dairy products and fish (study).
Opposite to what happens with Vitamin D or Omega-3, L-Carnitine deficiency is not prevalent nowadays.
Where Does L-Carnitine Work?
L-Carnitine may not be the best aid for fat loss. But that doesn't mean it's useless
L-Carnitine can help you improve your health and different aspects of our metabolism.
L-Carnitine Improves Muscle Recovery
Resistance training produces large amounts of oxidative stress and muscle damage.
L-carnitine supplementation increases blood flow and oxygen delivery to the muscle cells, reducing hypoxia conditions and cell disruptions associated with it (study).
In this study (study), 3 weeks of 1g/day L-Carnitine improved the vascular function and flow-mediated dilation.
Hypoxia has a negative effect on muscle recovery (study). If L-Carnitine reduces hypoxia conditions, it can help you on the recovery process.
L-Carnitine Show Antioxidant Capacity
Production of ROS species and excess oxidative stress is usual after resistance training.
A chronic oxidative stress reduces our lifespan and health (study).
L-Carnitine inhibits ROS-generating enzymes (study) and directly reduces ROS species (study).
It also shows to protect mitochondria and improve its integrity and function. This could indirectly increase antioxidant capacity as well (study).
Brain Function is Regulated by L-Carnitine
Brain function is one of the first physiological process to start deteriorating.
The form of L-Carntine ALCAR (Acetly-L-Carntine) shows promising results on brain function and health (study).
Experiments done with rats improve working memory and brain function by increasing synaptic neurotransmissions (study).
ALCAR increases nerve growth factor and activity of acetylcholine (study).
While advanced mental disorders don't seem to improve by ALCAR supplementation (systematic review), mild mental disorders and early stages could be improved by L-Carnitine (study).
ALCAR may improve mild mental disorders by enhancing collinergic activity, promoting energy metabolism, restoring the synaptic function and showing potential neurotrophofic effects (study)
Conclusion
L-Carnitine is a quaternary amine involved in fats transport into the mitochondrial matrix. However, because its function depends on the activity and efficiency of the enzymes catalyzing this step, L-Carnitine supplementation doesn't improve fat loss.
In this post we have seen other potential benefits of L-Carnitine. It may help improving muscle recovery, lowering oxidative stress, and more importantly, modulating brain function and protecting from mental disorders.
