L-Carnitine is a naturally occurring amino acid found in animal tissue (meat products). It can be acetylated to produce acetyl-L-carnitine (ALCAR), which is similar but crosses the blood-brain barrier more efficiently. L-Carnitine L-Tartrate (LCLT) is a form of L-carnitine that is used in a lot of studies in athletes as it’s thought to have a more rapid influx into plasma following oral ingestion (which makes it useful for timing-critical situations, like pre-workout dosing).
L-Carnitine can be synthesised endogenously (made within our bodies) with the dietary amino acids lysine and L-methionine. Given this, it would made sense for vegetarians to supplement L-carnitine, but there is a lack of human based research on the matter. L-Carnitine is best known for its involvement in the mitochondrial oxidation of long-chain fatty acids and so is often associated with fat loss products.
What are the clinical doses?
The standard dose for L-carnitine is between 500-2,000mg.
There are various forms of carnitine supplements. Acetyl-L-Carnitine (ALCAR) is generally used for cognitive enhancement, whereas L-Carnitine L-Tartrate (LCLT) is typically used for physical performance and power output. The equivalent dosage ranges for these are 630-2,500mg (ALCAR), and 1,000-4,000mg (LCLT).
What does it do?
The main function of L-carnitine is the transport of long-chain fatty acids into the mitochondrial matrix for their conversion in energy. L-Carnitine also plays an important role in the regulation of metabolic pathways involved in skeletal muscle protein balance. As L-Carnitine acts as anti-oxidant and anti-inflammatory compound, it may attenuate exercise-induced muscle damage. When it comes to fat-burning, studies in isolation don’t show very good results for fat loss with L-Carnitine. Some studies have found minor fat loss, however, this may in fact be linked to increased physical activity due to increased energy levels. It's possible that very low carnitine levels could lead to impaired fatty acid oxidation, but for most people, there isn't a notable increase in resting fatty acid oxidation when taking carnitine as low carnitine levels aren’t common.
Studies performed on moderately obese women with a dosage of 2g L-Carnitine daily and aerobic exercise didn’t show any significant effects on fat mass or body weight (Villani et al., 2000).
TLDR – L-Carnitine is often found in weight loss/fat burning supplements and drinks, with standard dosing ranging between 0.5-2g, however, scientific evidence for its efficacy in promoting fat loss and body composition improvement is limited.
Brandsch, C. and Eder, K., 2002. Effect of L-carnitine on weight loss and body composition of rats fed a hypocaloric diet. Annals of nutrition and metabolism, 46(5), pp.205-210.
Melton, Keenan, Stanciu, Hegsted, Zablah-Pimentel, O’Neil, Gaynor, Schaffhauser, Owen, Prisby and LaMotte, 2005. L-carnitine supplementation does not promote weight loss in ovariectomized rats despite endurance exercise. International journal for vitamin and nutrition research, 75(2), pp.156-160.
Sawicka, A.K., Renzi, G. and Olek, R.A., 2020. The bright and the dark sides of L-carnitine supplementation: a systematic review. Journal of the International Society of Sports Nutrition, 17(1), pp.1-10.
Villani, R.G., Gannon, J., Self, M. and Rich, P.A., 2000. L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. International journal of sport nutrition and exercise metabolism, 10(2), pp.199-207.