l-carnitine

Can L-Carnitine Help You Burn More Fat?

L-Carnitine is a amino acid derivative involved in energy metabolism and fat transport. Used as a supplement for fatloss phases, here we'll review its main effects, uses and benefits. And more importantly; 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 (more about fat loss HERE).

L-Carnitine can also be provided through three different ways:

  1. Supplementation: different formulas of L-Carnitine provide exogenous L-Carnitine
  2. Dietary sources: foods like meats or fish naturally contain L-Carnitine
  3. Dietary amino acids: intakes of lysine and methionine will be used to form L-Carnitine

Dietary sources are generally very low in L-Carnitine (study). To reach the recommended 0.5-2g, one cannot rely completely on diteary sources. Luckily, our body is able to synthesize it from lysine and methionine, and sufficient protein intake should be sufficient to produce enough L-Carnitine (study).

L-Carmitine food content

L-Carnitine is accumulated in cells and retained by kidneys using OCTN2, an organic cation transporter specific for carnitine (study). Deffects on OCTN2 may cause L-Carnitine deficiency. In these cases, L-Carnitine supplementation my be of interest.

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, on the other hand, will be converted to Acetyl-CoA, initiator of the TCA cycle (study)

Transport of fatty acids

Besides its role in fat metabolism, L-Carnitine also replaces acyl groups as acylcarnitines, preventing from accumulation of toxic compounds in the mitochondria (study). L-Carnitine has shown to modulate cytochrome C release, modulate palmitoyl-CoA dysfunction, and reduce mitochondrial swelling induced by long-chain fatty acids (study). In other words, L-Carnitine may act as a policeman controlling mitochondrial homeostasis and preventing accumulation of undesired compounds.

Based on this, we can speculate L-Carnitine to have a protective effect on mitochondrial function, enhancing both directly and indirectly fat transport an oxidation (study)

L-CARNITINE TO BURN FAT

Used as a supplement, L-Carnitine has always be claimed to act as a fat burner, enhancing fat oxidation and consequent fat loss.

Science Evidence

Studies show controversial results regarding he use of L-Carnitine to burn fat. Studies show how supplementing with L-Carnitine doesn't translate into an increase of muscle carnitine (study). On the other hand, 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 has shown to increase fat oxidation (study). Subjects with L-Carnitine deficiency also seem to benefit from L-Carnitine supplementation, increasing fat oxidation and modulating energy metabolism (study)

Recent studies ave suggested an increase in muscle carnitine when co-ingested for long periods with carbohydrates (study)(study). Traditional studies only investigated the effect of acute ingestion of L-Carnitine. This is the perfect example of the importance of timing when talking about sports supplements.

Can L-Carnitine be used to burn fat?

As you have seen, results are quite controversial. While acute ingestion of L-Carnitine on healthy and physically active subjects doesn't seem to have an effect on fat oxidation, obese or deficient on L-Carnitine subjects could benefit from L-Carnitine supplementation.

On the other side, chronic co-ingestion with carbohydrates does 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 therefore be a problem for some people.

Why Doesn’t L-Carnitine Work?

Here, there are some points to touch upon and discuss why L-Carnitine doesn't work as "fat burner".

It’s 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. Even with higher carnitine levels in the muscle, if the enzymes are not able to handle more substrate, the reaction would remain unchanged (study).

Studying general enzyme kinetics, one can observe how the reaction rate reaches a plateau-like region when the enzyme's active site is fully saturated. This is like a person eating burgers. If he has ten burguer to eat, he'll finish the 10 burguers in 10min. If he has 100 burguers, he'll finish the same 10 burguers in 10min, since he's not able to go faster.

Enzyme Kinetics

If carnitine levels go beyond Vmax, the reaction rate will not further increase, remaining uchanged. This it what happens with fat transport. The enzyme is the limiting factor, and increasing L-Carnitine levels doesn't seem to modulate fat transport and oxidation.

It’s NOT Essential

L-Carnitine is not essential. We can synthesize it from Lysine and Methionine (study). Following nutritional recommendations, you should be able to provide enough of these amino acids to reach recommended L-Carnitine levels.

Food can not only provide amino acids to indirectly increase L-Carnitine, but some also contain L-Carnitine, with the highest levels found in red meat, dairy products and fish (study). So, contrary to what happens with some other biomolecules such as Vitamin D or Omega-3, L-Carnitine deficiency is not prevalent nowadays.

Biosynthesis of L-Carnitine

WHERE DOES L-CARNITINE WORK?

We have seen how L-Carnitine may not be the best aid for fat loss. But that doesn't mean its supplementation is useless. Its presence on the mitochondria makes it a good candidate to improve our health and different aspects of our metabolism.

Benefits of L-Carnitine

L-CARNITINE IMPROVES MUSCLE RECOVERY

Physical exercise, more importantly resistance training induce large amounts of oxidative stress and muscle damage. Therefore, an aspect to treat on this aspect is muscle recovery, which may improve the anabolic response and further adaptations (study).

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 other study (study), 3 weeks of 1g/day L-Carnitine improved the vascular function and flow-mediated dilation.

Hypoxia conditions have shown to have a negative effect on muscle recovery (study). If L-Carnitine reduces hypoxia conditions, can therefore prevent from excess muscle soreness and induce an earlier recovery.

L-CARNITINE SHOWS ANTIOXIDANT CAPACITY

Production of ROS species and excess oxidative stress is usual after resistance training. Although this status is necessary to induce anabolic responses and build muscle, a chronic oxidative stress reduces our lifespan and health (study).

L-Carnitine has shown, in human cells cultures, to inhibit ROS-generating enzymes (study) and directly reduce ROS species (study). Not only that, but it also shows to protect mitochondria and improve its integrity and function. This could indirectly increase antioxidant capacity as well (study).

Although the results seem quite promising, they are yet mere theories and studies performed with cells an rodents. So, to get practical conclusions, we'll have to wait...

L-Carnitine antioxidant

BRAIN FUNCTION IS REGULATED BY L-CARNITINE

As we age, brain function is one of the first physiological process to start deteriorating. The high prevalence of mental disorders in old subjects makes this field of research quite of a high interest, and a lot of substances are being tested to try prevent this to happen.

The form of L-Carntine ALCAR (Acetly-L-Carntine) shows quite promising results on brain function and health (study).

Experiments done with rats show an improved working memory and brain function by increasing synaptic neurotransmissions (study). Also in aging rats, ALCAR shows to increase nerve growth factor and activity of acetylcholine (study).

In humans, the evidence is quite more controversial. 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).

The mechanisms of action are yet not well understood. However, ALCAR may improve mild mental disorders by enhancing collinergic activity, promoting energy metabolism, restoring the synaptic function and showing potential neurotrophofic effects (study)

But, once again, these results are promising but still quite unreliable. So, patience and stay updated for coming studies!

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.

However, 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.

If you still have doubts, please leave it below in the comments section!!

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