L-Carnitine: What Makes It The Most Popular Amino Acid Supplement?

L-Carnitine is an amino acid that is naturally found in some foods- highest in red meat and dairy. 

It was first isolated in 1905 from meat, leading to its name from the Latin word “carnis” meaning flesh [1].

Its primary function is the metabolism of fatty acids by transporting them into the mitochondria and aiding mitochondrial function.

Conditionally Essential

We discussed what essential vs non-essential amino acids are in our recent article on essential amino acids. Basically, what makes an amino acid essential is if it cannot be produced endogenously by the body and must thus be obtained through diet (or supplements).

L-Carnitine is a “conditionally essential” amino acid i.e. it is essential only in certain conditions such as this genetic abnormality hindering carnitine synthesis, pregnancy, and often a vegan/vegetarian diet.

What Makes it So Popular? Role in Fat Loss And Energy Production

L-Carnitine is not even an essential amino acid, and yet it is the most popular among all of the L-prefixed names(amino acids) in the supplements world. The reason for that is its role in fat loss and energy production. Between practically the entire population today trying to lose excess fat, and athletes and bodybuilders trying to boost performance- amplifying these two functions are the most coveted goals in the health space today.

But L-Carnitine has multiple other noteworthy benefits too. A specific form of L-Carnitine, Acetyl-L-carnitine which can cross the blood-brain barrier and enter the brain, has been shown to have significant cognitive benefits. It has been shown to prevent age-related cognitive decline and improve neurodegenerative conditions. And to improve cognitive function in general [2].

However, there have been some contradictory studies as well [3].

Powerful Effects Against Depression

The effects of Acetyl-L-carnitine supplementation on depression have been very promising with multiple studies showing it to be effective. Studies comparing it to antidepressant drugs have shown it to be equally effective but without the adverse effects [4].

L-Carnitine: The Different Available Forms

There are 3 forms that are sold as supplements:

L-carnitine L-tartrate: This is what’s usually referred to as just “L-Carnitine”. This is the most common form of the supplement. It helps boost energy levels and aids fat loss.

Acetyl-L-carnitine: Also known as ALCAR. As discussed above, this form is able to cross the blood-brain barrier and benefit the brain in various ways.

Propionyl-L-carnitine: This form is suited for circulatory issues like peripheral vascular disease and high blood pressure. Some older research indicates it may enhance blood flow by increasing nitric oxide production.

Other Benefits

Let’s go through all of the other purported benefits of L-Carnitine.

Weight Loss

L-carnitine can be used as a weight loss supplement because it helps move fatty acids into your cells to be burned for energy. Several studies have shown that L-carnitine supplementation can significantly reduce body weight, body mass index (BMI), and fat mass [5] [6]

Heart Health

Some studies suggest that L-carnitine may benefit various aspects of heart health. It has been found to reduce diastolic blood pressure, improve heart function, and decrease symptoms in people with congestive heart failure. Additionally, L-carnitine can help lower total and LDL cholesterol while increasing HDL cholesterol in people at risk for heart disease. [7] [8]

Exercise Performance

Although the overall data on it is a little mixed, there is enough promising evidence of L-Carnitine on exercise performance to warrant its use. 

It has been shown to improve exercise recovery, increase muscle oxygen supply, boost stamina, reduce muscle soreness after exercise, and promote the production of red blood cells that transport oxygen to the muscles. When taken 60-90 minutes before working out, L-carnitine could potentially enhance high-intensity exercise performance. [13] [14] [15][16][17]

Type 2 Diabetes

L-carnitine may be beneficial for individuals with type 2 diabetes. Studies suggest that supplementation with L-carnitine can help lower fasting blood sugar and hemoglobin A1c levels while improving insulin sensitivity in people with diabetes, overweight, or obesity. It is believed to work by affecting insulin receptors and specific genes that regulate sugar metabolism. Additionally, L-carnitine may improve the function of beta cells responsible for producing insulin in the pancreas. [9] [10].

Are There Any Downsides?

It’s not natural to be consuming L-carnitine in the amounts we get in supplements today. Because we only get around 300-400 mg at max from food sources. So it does raise the question of how safe these supplements are.

Multiple studies have shown doses of up to 2g to be safe for long-term use [11].

There is one known adverse effect though. Ingesting high amounts of L-carnitine alters the gut microbiome to increase the amount of carnitine-fed bacteria in the gut. This in turn raises serum levels of trimethylamine-N-oxide (TMAO), which is associated with adverse effects on cardiovascular health. More research is needed to get to the bottom of this concern.


l-carnitine dietary supplement for heart health workout fitness

Bioavailability: Food vs Supplements

As an exception to the general trend, supplemental forms of L-carnitine actually have lower bioavailability compared to food sources.

Supplemental forms have been shown to have a bioavailability of 14-18% whereas food sources have 57-84% [12].

So Should You Take It? 

As mentioned earlier L-carnitine has been classified as “conditionally essential”. There is a good amount of evidence to show that the body is capable of making sufficient quantities by itself and we get a good amount through diet as well.

Supplementation may be necessary for certain people though:

  • Vegetarians and vegans who don’t get any L-carnitine via diet
  • Older people who face higher rates of neurodegeneration
  • Athletes who have increased demands
  • Pregnant women

A comprehensive blood panel can reveal whether or not you require L-carnitine supplementation. Reach out to a good functional medicine practitioner for this.

Lastly, even though it may not be “necessary”, you could still benefit from supplementation, as all the studies mentioned here reveal. That’s what biohacking is all about. Just use some good old trial-and-error to see if it works for you.

Does iThrive Essentials Have an L-Carninite Supplement?

We don’t have a dedicated L-carnitine supplement (not yet at least). But great news- our CoQ10 supplement includes 500 mg of L-carnitine per serving. So should you take CoQ10 too then? That’s for another day. Stay tuned (or just forget all of this. It’s too complex. Just eat and sleep well and relax).


  1. https://journals.physiology.org/doi/10.1152/physrev.1983.63.4.1420?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%20%200pubmed
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7284336/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6464592/
  4. https://pubmed.ncbi.nlm.nih.gov/29076953/
  5. https://pubmed.ncbi.nlm.nih.gov/32359762/
  6. https://pubmed.ncbi.nlm.nih.gov/27335245/
  7. https://pubmed.ncbi.nlm.nih.gov/31481697/
  8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5406747/
  9. https://pubmed.ncbi.nlm.nih.gov/36704801
  10. https://pubmed.ncbi.nlm.nih.gov/36704801
  11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7507632
  12. https://www.ncbi.nlm.nih.gov/pubmed/15591001 

Other References

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