Carnitine as a fat burner
Carnitine, much like creatine (even though their functions are quite different) is a supplement that has been available for years (even decades). It has always been categorized by common wisdom as a « fat burner » or « fat mobilizer », and considered by better informed parties as a placebo product because no study (until very recently) had been able to prove the efficacy of oral carnitine supplementation regarding fat oxidation.
Let’s take a closer look at the substance itself : Carnitine is a naturally occurring compound made of several amino acids that is synthesized in the kidneys and liver and that can also be found in meat and dairy products. Its primary role is related to energy metabolism in mammals. In summary, the function of carnitine is to carry long-chain fatty acids into the mitochondria (cell organ responsible for energy production), in order for those to be oxidized and produce energy, and to carry short-chain fatty acids out of the mitochondria.
This is why carnitine supplementation was long thought to have a « fat burning » effect. Indeed, the theory was that during physical exercise requiring a lot of energy, if the amount of carnitine in muscle cells was elevated, fatty acid oxidation would increase, enhancing the consumption of fat as a substrate for energy production, resulting in a lowered body fat percentage and a sparing of muscle glycogen (which would lead to sustained performances).
And even though it makes perfect sense in theory, up until 2011, no study had been able to scientifically prove the efficacy of carnitine supplementation in regards to fatty acids oxidation and fat loss. The main problem was that oral supplementation of carnitine didn’t result in an increase in actual carnitine levels inside the cells (muscle cells in that case). Therefore, no augmentation of fatty acid oxidation, or significant changes in body composition were witnessed.
The solution to that problem was found and exposed in two studies conducted by Wall et al. in 2011 and 2013. What they did was to add eighty grams of a carbohydrate rich beverage to each dose of carnitine supplementation in order to generate an insulin response that allowed for an optimal absorption of carnitine by the muscle cells.
As a result, levels of carnitine inside the muscle cells increased greatly (twenty percent) after a period of twelve weeks, resulting in a reduction of fifty percent in glycogen use, an increase of thirty-five percent in work output and no measurable weight gain despite the daily increase of a hundred and sixty grams of carbohydrate, as opposed to the control group who consumed the carbohydrate beverage without the carnitine and gained 1.8 kg in average, almost entirely in fat mass.
The other noticeable fact regarding the supplementation protocol of the two studies is the amount of carnitine. The subjects ingested two daily doses of 1.36 grams, which amounts to a daily total of almost three grams. This is much more than the daily carnitine intake (between 1 and 1.5 grams) usually recommended by the supplementation industry.
The last but perhaps the most important observation made by Wall et al. throughout those two studies is the increase in the expression of different genes responsible mainly for insulin signalling, and fat oxidation, resulting in better insulin sensitivity. This means that carnitine supplementation might have beneficial and therapeutic effects on obese and/or insulin resistant people.
How to use it ?
If we want to learn from those researches and apply their findings, here is how carnitine supplementation should occur : always ingest carnitine with at least eighty grams of carbohydrate ; that doesn’t mean you have to eat more sugar, or even change your eating habits. Just make sure to take carnitine with a big, carbohydrate rich meal. In contrast with what is usually advised on carnitine products, the time of ingestion related to training sessions seems to be irrelevant. During the studies, the subjects consumed carnitine in the morning after waking up and then four hours later (most likely at lunch), independently to when they trained.
Also, as mentioned in the precedent chapter, carnitine consumption increases overall energy expenditure and fat oxidation, therefore, it is not advised for someone who is trying to gain weight (whether for health or athletic related reasons) to supplement with carnitine, this would defeat the purpose.
Even if over-supplementation should always be a concern, beware of the industry’s recomandations regarding the daily intake of carnitine, they tend to be insufficient for actual results (2.5 to 3 grams of carnitine per day being the ideal dosage, if we trust Wall et al.)
Even though no dangerous or undesirable side effects of carnitine supplementation have been observed so far (except for people suffering from seizures and hypothyroidism, carnitine might actually worsen their symptoms), it is important to be aware of the exact composition and quality of the supplement used. A lot of « fat burning » products that carry the « L-Carnitine » label, also contain filling products (Caffeine, green tea extract etc…) that are supposed to facilitate weight loss, but their actual potency in that regard is relative and when consumed in excess, they can have undesirable side effects.
Patience is also key, the studies showed great results after twelve weeks and even better after twenty-four weeks. So do not expect measurable effects before three months of supplementation.
One last factor to keep in mind, the efficiency of carnitine supplementation is closely linked to exercise, all the subjects in the two studies were recreational athletes who exercised on a regular basis. Carnitine supplementation alone (without a well designed training program) cannot generate noticeable changes in body composition.
Other benefits of carnitine supplementation
Carnitine supplementation has been shown to efficiently relieve symptoms of hyperthyroidism in a matter of weeks.
Acetyl-l-Carnitine supplementation over a one year period has been shown to slow down neurodegeneration in cases of dementia and Alzheimer’s disease, mainly in patient younger than 61 years old. Probably due to carnitine’s support to mitochondrial health and function, that probably results in a reduction of oxidative brain damage.
Different forms of carnitine available
Carnitine is available as a supplement in a variety of forms :
L-carnitine: the most widely available and least expensive, the kind that is used as a performance/fat loss supplement.
Acetyl-L-carnitine: Often used in studies for Alzheimer’s disease and other brain disorders.
Propionyl-L-carnitine: Often used in studies for heart diseases and peripheral vascular diseases.
Avoid D-carnitine supplements. They interfere with the natural form of L-carnitine and may produce unwanted side effects.
In summary, it took several decades, but carnitine has finally proved to be everything we hoped it was, providing we respect a precise supplementation protocol to allow for its optimal absorption and effects. Those effects being increased overall energy expenditure, increased fatty acids oxidation, resulting in weight loss, or weight gain prevention. Also, reduced glycogen use, resulting in lower lactate accumulation and increased work output, as well as enhanced insulin sensitivity.
Carnitine was also found to have great therapeutic potential against insulin resistance and Alzheimer’s disease.
Acetyl-L-carnitine physical-chemical, metabolic, and therapeutic properties : relevance for its mode of action. J. W. Pettegrew, J. Levine and R. J. McClure
Acetyl-L-CarnitinesSupplementation differently Influences nutrient partitioning, serum leptin concentration and skeletal muscle mitochondrial respiration in young and old rats. Susanna Iossa, Maria Pina Mollica, Lilla` Lionetti, Raffaella Crescenzo, Monica Botta, Antonio Barletta and Giovanna Liverini. Department of General and Environmental Physiology, University of Naples “FEDERICO II,” Italy. 2002.
Carnitine, The science behind an essential nutrient. Geltrude Mingrone, MD, PHD, Catholic Uiversity, Rome, Italy.
Carnitine, metabolisme and functions. Jon Bremer, University of Oslo Norway, 1983.
Acetyl-L-carnitine improves aged brain function. Kobayashi S, Iwamoto M, Kon K, Waki H, Ando S, Tanaka Y.
Comparison of the Effects of l-carnitine and acetyl-l-carnitine on carnitine levels, ambulatory activity, and oxidative stress biomarkers in the brain of old rats. Jiankang Liu, Elizabeth Head, Hirohiko Kuratsune, Carl W. Cotman, Bruce N. Ames, 2006.
Carnitine and sports medicine: Use or abuse? Eric P. Brass, M.D., Ph.D. Professor of Medicine, UCLA School of Medicine Director, Harbor UCLA Center for Clinical Pharmacology
Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study. Paolo Colombani,, Caspar Wenk, Iris Kunz, Stephan Kr.henbühl, Martina Kuhnt, Myrtha Arnold, Petra Frey‐Rindova, Walter Frey, Wolfgang Langhans.
Influence of carnitine supplementation on muscle substrate and carnitine metabolism during exercise. M. Soop, O. Bjorkman, G. Cederblad, L. Hagenfeldt, and J. Wahren. 1988.
The effect of supplementary dietary L-carnitine on the growth performance, serum components, carcase traits and enzyme activities in relation to fatty acid β-oxidation of broiler chickens. T-F. Liena & Y-M. Hornga 2010.
Carnitine supplementation : effect on muscle carnitine and glycogen content during exercise. Matthew D. Vukovich, David L. Costill, and William J. Fink, 1994.
Carnitine supplementation in sports. Giuseppe Alamia, University of Palerm, Italy, 2013.
Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. Benjamin T.Wall, Francis B. Stephens, Dumitru Constantin-Teodosiu, Kanagaraj Marimuthu, Ian A. Macdonald and Paul L. Greenhaff. 2011.
Dietary Supplements for Improving Body Composition and Reducing Body Weight: Where Is the Evidence? Melinda M. Manore, International Journal of Sport Nutrition and Exercise Metabolism, 2012.
Effect of carnitine on thyroid hormone actions. Salvatore Benvenga, MD, 2004.
L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress. Jeff S. Volek, William J. Kraemer, Mrtyn R. Rubin, Ana L. Gomez, Nicholas A. Ratamess, and Paula Gaynor, 2001.
Overexpression of Carnitine Palmitoyltransferase-1 in Skeletal Muscle Is Sufficient to Enhance Fatty Acid Oxidation and Improve High-Fat Diet–Induced Insulin Resistance. Clinton R. Bruce, Andrew J. Hoy, Nigel Turner, Matthew J. Watt, Tamara L. Allen, Kevin Carpenter, Gregory J. Cooney, Mark A. Febbraio, and Edward W. Kraegen, 2008.
Age-associated mitochondrial oxidative decay: Improvement of carnitine acetyltransferase substrate-binding affinity and activity in brain by feeding old rats acetyl-Lcarnitine and_or R-lipoic acid. Jiankang Liu, David W. Killilea, and Bruce N. Ames, 2002.
Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans. Francis B. Stephens, Benjamin T.Wall, Kanagaraj Marimuthu, Chris E. Shannon, Dumitru Constantin-Teodosiu, Ian A. Macdonald and Paul L. Greenhaff, 2013.
The Effect of L-carnitine on Fat Oxidation, Protein Turnover, and Body Composition in Slightly Overweight Subjects. Klaus D. Wutzke and Henrik Lorenz, 2004.