Acetyl-L-Carnitine - the Science

The body can make use of different nutritional sources to produce energy, the major ones being carbohydrates, proteins, and fats. When fatty acids are absorbed into the blood, or released into the blood from adipose tissue, they can be utilized by other cells to generate energy. Some fatty acids can be readily used to generate energy. Others, specifically long-chain fatty acids, require further processing in order to be used for energy generation.

It is in this further processing that carnitine plays a vital role. Whereas short and medium chain fatty acids can readily pass through the mitochondrial membrane to be metabolized, long chain fatty acids cannot. Carnitine is used to bring these long chain fatty acids into the mitochondria in a process called the Carnitine Shuttle.

In the Carnitine Shuttle, carnitine binds to the long chain fatty acid, which makes the fatty acid now able to cross the previously impermeable membrane. The bound fatty acid now enters into the mitochondria. Once transported in, the carnitine can now be removed, as the fatty acid is now in the desired location and available for metabolism. The carnitine is then recycled, and can be used to bring further long chain fatty acids into the mitochondria. A diagram is provided below in order to help visualize this process.

As you can imagine, this process makes carnitine vital for the body to be able to effectively metabolize fats and generate energy. Carnitine also plays various other roles in the body due to its ability to bind and release acyl groups. 

The etymology of the word "carnitine" comes from the Latin word "carn" or "carnis", which means "flesh" or "meat". This is because carnitine is found largely in dietary sources of meat, and because carnitine was first isolated from meat extracts. This may indicate that vegetarians or vegans can especially benefit from carnitine supplementation. Many people, regardless of dietary considerations, may benefit from carnitine supplementation, given its vital role in metabolic processes.

References:

Browna. (n.d.). 6.32 Fatty acid Oxidation (Beta-oxidation) | Nutrition Flexbook. https://courses.lumenlearning.com/suny-nutrition/chapter/6-32-fatty-acid-oxidation-beta-oxidation/

carnitine. (n.d.). In Merriam-Webster Dictionary. https://www.merriam-webster.com/dictionary/carnitine

JJ Medicine. (2018, August 25). Carnitine Shuttle | Purpose and mechanism [Video]. YouTube. https://www.youtube.com/watch?v=ueQqdrqBGiU

Office of Dietary Supplements - Carnitine. (n.d.). https://ods.od.nih.gov/factsheets/Carnitine-HealthProfessional/