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Myths and Truths – Carnitine Supplementation

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Myths and Truths – Carnitine Supplementation

A woman holding pills and water

TLDR BOX

  • Carnitine is an amino acid naturally found in the body;
  • L-carnitine is the biologically active form absorbed from foods by your gut;
  • It plays an important role in brain function and in the production of energy
  • It can..
    • help you recover better after a workout and provide more oxygen for your muscles
    • improve your stamina, strength and power
  • It may provide benefits regarding cardio-vascular diseaseas and type two diabetes
  • There are no notable benefits regarding weight loss and carnitine supplementation
  • Usually at doses of approximately 3 g/day different adverse reactions can occur

HOW CARNITINE WORKS AND WHAT IS IT?

Even though this is a very popular supplement I would still like to start this article with the definition of it. Carnitine is a nutrient and a dietary supplement. It’s an amino acid that often is supplemented by bodybuilders and by people who want to lose weight. It’s true that most ads say you can use it for weight loss or improve brain function. But does it really work like they say?

You may ask what is the deal with the ”L” added in front of carnitine which can be found on most supplement selling websites. L-carnitine is the biologically active form absorbed from foods by your gut. [1] There is also a D-carnitine but that is the inactive form of the compound. You can say that carnitine is a general term that includes the other forms as well. More than 90% of carnitine storages are in skeletal muscles and in the heart so maybe this is why this supplement was so interesting to study. [4]

There are different types of carnitine:

  • Acetyl-L-carnitine (ALCAR)
  • Propionyl-L-carnitine 
  • L-carnitine L-tartrate (this might aid your recovery process) [2]

The first two forms may help people suffering from various medical conditions but there is a need for more studies to confirm this.

Mostly L-carnitine and Acetyl-L-carnitine are the most effective for general usage and that is why you can find them easier. 

WHAT CARNITINE DOES?

Carnitine plays an important part in the process of energy production by transporting fatty acids into your cells’ mitochondria – the powerhouse of the cell, the “energy producer” that turns these fatty acids into energy to support your activities. [3] 

Your body can sustain carnitine levels by combining two aminoacids, methionine and lysine, but in order for your body to produce enough you need a substantial level of vitamin C.[4]

What about Carnitine Levels? 

Some good sources can be fish, poultry and milk but red meat is still the best one. [5] As you can see, these sources may not be handy for a vegetarian or a vegan so carnitine can be considered a conditionally essential nutrient. [6] Even if you don’t supplement you can keep a normal level of carnitine because your body will absorb most of it. And if the level is too high your body will excrete the excess. [33] For people with carnitine deficiency, it represents a serious medical condition.The incidence of primary carnitine deficiency in the general population is approximately 1 in 100,000 newborns. It can manifest through muscle weakness, stunted growth, an enlarged liver, and a number of other problems. (Metabolic myopathies caused by disorders of lipid and purine metabolism. Author: Basil T Darras, MD)

CARNITINE BENEFITS

Regarding the benefits of carnitine, I would like to state two different kinds of benefits: in general health and in the fitness niche including the very popular effect, fat loss which will be discussed separately.

Recovery [7] (the study used L-carnitine L-tartrate)

This study investigated the effects of oral L-carnitine supplementation on pain (VAS scale), tenderness (pain thresholds) and CK (creatine kinase) release induced by a 20-min eccentric effort of the quadriceps muscle. Creatine kinase is a compound that is increased after strenuous sporting activity so high levels aren’t showing a good recovery. The conclusion of the study was that the L-carnitine supplementation DID alleviate pain, tenderness and reduced the levels of CK. [8]

Improve your Stamina, Strength and Power 

It may increase the flow of blood and the production of nitric oxide (enlarges blood vessels) and therefore reduce fatigue [9] (the study used L-carnitine L-tartrate)

A recent study targeted exercise performance, anaerobic power and stress-induced oxidative stress in resistance-trained men by splitting 23 men into two groups. Eleven of them ingested placebo and twelve  of them ingested L-carnitine 2 g per day for nine weeks and resistance training in parallel (upper-lower body split 4 d/w).  There were significant increases in bench press lifting volume at week six and nine of check-ups and a similar result was noticed for leg press regarding the L-carnitine group. Also there were noticeable increases in mean power and peak power, reduction in post-exercise lactate levels (usually measured to quantify endurance) and some benefits regarding antioxidants levels. [10]

As you can see in this graphics, there were significant increases in bench press lifting volume at week-6 check-ups (146 kg, 95% CI 21.1, 272) and week-9 check-ups (245 kg, 95% CI 127, 362) with L-carnitine. A similar trend was observed for leg press. In the L-carnitine group, at week-9, there were significant increases in mean power (63.4 W, 95% CI 32.0, 94.8). The graph is from M. S. Koozehchian et al. study. The carnitine group is the one with the black dot on the graphs. 

Endurance

Another study proved that 3 or 4 g of L-carnitine taken before physical exercise can prolong exhaustion. They included 26 professional footballers and checked their endurance. One group took 3 g of carnitine and to the other group 4 g of carnitine and after running both groups had their  level of lactate measured. After one week they repeated the test with placebos for everyone and the compared result showed statistically significant less lactate and a decreased heart rate response compared to the same speed they ran. [11]

Aging

As the human body ages, the mitochondrias do as well. You know, the powerhouse of the cell we talked about earlier. Carnitine might come in handy as these studies show. [12]  I must say that this study was performed on rats and it showed that supplementation with acetyl-L-carnitine and lipoic acid improved their performance in memory tests and reduced mitochondrial delay. [13]

We need research on humans to confirm the benefits of carnitine on aging.

Cardiovascular Diseases

Carnitine was studied for its effects on the cardiovascular system especially cardiac ischemia (restriction of blood flow to the heart) and peripheral arterial disease. [14] [15] I won’t write much about this but I really want to tell you about this meta-analysis. They concluded that treatment with L-carnitine in patients experiencing a cardiac arrest reduces all-cause mortality by 27%, ventricular arrhythmias (abnormal hearbeats) by 65%, and ischemia by 40% over a median follow-up period of 2 months, but does not reduce the risk of heart failure (weakening of the heart)or recurrence of heart attacks. [16]

The Role in Ischemia and Oxygen Supply

Claudication is a disease where an inadequate supply of oxygen-rich blood to the legs leads to a high level of acetyl-carnitine in the muscles. These patients experience significant impairments in exercise performance and have difficulty walking even short distances at a slow speed. [15]  A multicenter trial in the United States and Russia found that carnitine administered for 6 months in patients with disabling claudication significantly improved walking distance and speed, reduced bodily pain, enhanced physical function, and improved perceived health state compared to patients in the control group. [17] The authors of a systematic review and meta-analysis that included these and 12 other randomized clinical trials concluded that propionyl-L-carnitine significantly increases peak walking distance in patients with claudication. [18]

Red Meat and Carnitine

However, the medical community has some concerns regarding the chronic supplementation with carnitine. Eating a lot of red meat (one of the principal sources of carnitine) has been linked to an increased cardio-vascular risk. Therefore some scientists think that this explains why in this study some participants (omnivorous) have produced TMAO (trimethylamine-N-oxide), a substance that is associated with cardiovascular disease risk. [19]

Type 2 diabetes

There was an association between fatty-acid oxidation in the muscles and insulin resistance. Increased levels of fat storages in muscles have become a marker of insulin resistance – a very important factor in the development of type 2 diabetes. [20] 

A recent analysis of subjects included in two clinical trials with either type 1 or type 2 diabetes found that treatment with acetyl-L-carnitine (3 grams/day orally) for one year provided significant relief of nerve pain and improved perception of vibrations in those with diabetic neuropathy (nerves are affected and sensibilities are less accurate). The treatment was most effective in subjects with type 2 diabetes of short duration. [21] 

 Future studies may confirm that carnitine can be an adjuvant in type 2 diabetes therapy.

Brain function

Even though this study is from 1991 I wanted to talk about it a bit because it had 130 participants with Alzeihmer’s. They measured 14 outcomes to assess functional and cognitive impairment. After one year of carnitine supplementation both the placebo and the treatment group worsen BUT the treated group showed a slower rate of deterioration in 13 of those 14 outcomes.  [22]

There are more old studies that confirm the effects of carnitine in different diseases like Alzheimer’s, senile brain or even the impairments that come with aging. [23],[24],[25]. 

Another study  on rats (we need human studies to confirm) showed that acetyl-L-carnitine may increase transmission of different neurotransmitters in the brain and therefore improve the learning ability of the rats. [26]

CAN I USE CARNITINE TO BURN FAT?

Of course you will tell me: ”Hey, carnitine delivers fatty-acids in order for them to be used so it can help me burn fat”… Well… That is true in theory but let’s look at the science facts which say it’s false.

The evidence is somewhat mixed. Let me explain:

For example, this study took 36 overweight premenopausal women and divided them into two groups. 18 of them ingested 2 g L-carnitine twice daily  and 18 were given placebo. All of them walked 30 min for four days per week. Only 15 women from the placebo group and only 13 women from the L-carnitine group completed the study. Guess what? No differences were observed when regarding total body mass, fat mass or lipid utilization over time comparing the 2 groups. The only notable difference is that 5 women from L-carnitine group experienced nausea or diarrhea. [27] 

The Black Swan Study?

You might tell me about the meta-analysis that proved carnitine can lead to weight loss. Nine studies were analyzed in the end and revealed that the participants who received L-carnitine lost 1.33 kg (MD) more than the rest.  [28]  BUT a letter to the editor wanted to clear up some facts (comment to the title of the article quoted). Only four of the nine studies used L-carnitine while the others used orlistat and sibutramine or changes in lifestyle. They considered this a methodological flaw that should be corrected. Also, there is a substantially variability between samples (obese, diabetic, bipolar disorder). Considering other studies that proved no effects they strongly suggest that the use of L-carnitine for weight loss seems not appropriated. Another important mention is that the author of the meta-analysis didn’t state risks or side effects. [29]

Rat & Cat Studies

There are some animals studies done on rats that proved no weight loss effect of carnitine [30] [31] but this study on overweight cats showed that the carnitine group had some benefits regarding the metabolic effect when they underwent rapid weight loss, meaning that carnitine facilitated fatty acid oxidation. [32]

That being said, there are no notable benefits from carnitine supplementation regarding weight loss. Sorry, no magic pill to get shredded. Diet still has to be on point if you want to lose body fat, no matter what training method you choose. Get your blueprint on fat loss success here.

ARE CARNITINE SUPPLEMENTS SAFE?

Usually at doses of approximately 3 g/day different adverse reactions can occur like: nausea, vomiting, abdominal cramps, diarrhea and a ”fishy” body odour. Rarer side effects include muscle weakness in uremic patients and seizures in those with seizure disorders. [33]

Some research indicates that intestinal bacteria metabolize carnitine to form a substance called TMAO that might increase the risk of cardiovascular disease (previously mentioned). This effect appears to be more pronounced in people who consume meat than in vegans or vegetarians. The implications of these findings are not well understood and require more research.[19]

TAKE HOME MESSAGE 

When To Use Carnitine?

First of all, I would say that you should use carnitine when and if your doctor prescribes it to you. 

As you can read above, there are no proven benefits regarding weight loss if you supplement with carnitine so I recommend not using it for this purpose. 

I stated some benefits regarding athletic performance and carnitine use. Feel free to supplement with carnitine if you consider so after reading them. I suggest you take carnitine pre-workout though. 

The other medical benefits I wrote should ALWAYS be discussed with your physician if you think about supplementing with carnitine for those specific reasons.

Article written by Vlad Radulescu

References
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[2] B. A. Spiering et al., “Responses of criterion variables to different supplemental doses of L-carnitine L-tartrate,” J. Strength Cond. Res., 2007.
[3] M. Inazu and T. Matsumiya, “Physiological functions of carnitine and carnitine transporters in the central nervous system,” Japanese Journal of Neuropsychopharmacology. 2008.
[4] A. Steiber, J. Kerner, and C. L. Hoppel, “Carnitine: A nutritional, biosynthetic, and functional perspective,” Mol. Aspects Med., 2004.
[5] J. Pekala et al., “L-Carnitine – Metabolic Functions and Meaning in Humans Life,” Curr. Drug Metab., 2011.
[6] K. A. Lombard, L. Olson, S. E. Nelson, and C. J. Rebouche, “Carnitine status of lacto ovo vegetarians and strict vegetarian adults and children,” Am. J. Clin. Nutr., 1989.
[7] W. J. Kraemer et al., “The effects of L-carnitine L-tartrate supplementation on hormonal responses to resistance exercise and recovery,” J. Strength Cond. Res., 2003.
[8] M. A. Giamberardino, L. Dragani, R. Valente, F. Di Lisa, R. Saggini, and L. Vecchiet, “Effects of prolonged L-carnitine administration on delayed muscle pain and CK release after eccentric effort,” Int. J. Sports Med., 1996.
[9] B. A. Spiering et al., “Effects of l-carnitine l-tartrate supplementation on muscle oxygenation responses to resistance exercise,” J. Strength Cond. Res., 2008.
[10] M. S. Koozehchian et al., “Effects of nine weeks L-Carnitine supplementation on exercise performance, anaerobic power, and exercise-induced oxidative stress in resistance-trained males,” J. Exerc. Nutr. Biochem., 2018.
[11] G. E. Orer and N. A. Guzel, “The effects of acute l-carnitine supplementation on endurance performance of athletes,” J. Strength Cond. Res., 2014.
[12] B. N. Ames and J. Liu, “Delaying the mitochondrial decay of aging with acetylcarnitine,” in Annals of the New York Academy of Sciences, 2004.
[13] T. M. Hagen et al., “Feeding acetyl-L-carnitine and lipoic acid to old rats significantly improves metabolic function while decreasing oxidative stress,” Proc. Natl. Acad. Sci. U. S. A., 2002.
[14] R. Ferrari, E. Merli, G. Cicchitelli, D. Mele, A. Fucili, and C. Ceconi, “Therapeutic effects of L-carnitine and propionyl-L-carnitine on cardiovascular diseases: A review,” in Annals of the New York Academy of Sciences, 2004.
[15] W. R. Hiatt, “Carnitine and peripheral arterial disease,” in Annals of the New York Academy of Sciences, 2004.
[16] J. J. DiNicolantonio, C. J. Lavie, H. Fares, A. R. Menezes, and J. H. O’Keefe, “L-carnitine in the secondary prevention of cardiovascular disease: Systematic review and meta-analysis,” Mayo Clin. Proc., 2013.
[17] W. R. Hiatt et al., “Propionyl-L-carnitine improves exercise performance and functional status in patients with claudication,” Am. J. Med., 2001.
[18] E. P. Brass, D. Koster, W. R. Hiatt, and A. Amato, “A systematic review and meta-analysis of propionyl-l-carnitine effects on exercise performance in patients with claudication,” Vasc. Med. (United Kingdom), vol. 18, no. 1, pp. 3–12, 2013.
[19] R. A. Koeth et al., “Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis,” Nat. Med., 2013.
[20] G. Mingrone, “Carnitine in type 2 diabetes,” in Annals of the New York Academy of Sciences, 2004.
[21] A. A. F. Sima, M. Calvani, M. Mehra, and A. Amato, “Acetyl-L-carnitine improves pain, nerve regeneration, and vibratory perception in patients with chronic diabetic neuropathy: An analysis of two randomized placebo-controlled trials,” Diabetes Care, 2005.
[22] A. Spagnoli et al., “Long–term acetyl–l–carnitine treatment in alzheimer’s disease,” Neurology, 1991.
[23] M. Sano et al., “Double-blind parallel design pilot study of acetyl levocarnitine in patients with alzheimer’s disease,” Arch. Neurol., 1992.
[24] G. Rai, G. Wright, L. Scott, B. Beston, J. Rest, and A. N. Exton-Smith, “Double-blind, placebo controlled study of acetyl-l-carnitine in patients with alzheimer’s dementia,” Curr. Med. Res. Opin., 1990.
[25] M. Passeri, D. Cucinotta, P. A. Bonati, M. Iannuccelli, L. Parnetti, and U. Senin, “Acetyl-L-carnitine in the treatment of mildly demented elderly patients,” in International Journal of Clinical Pharmacology Research, 1990.
[26] S. Kobayashi, M. Iwamoto, K. Kon, H. Waki, S. Ando, and Y. Tanaka, “Acetyl-l-carnitine improves aged brain function,” Geriatr. Gerontol. Int., 2010.
[27] R. G. Villani, J. Gannon, M. Self, and P. A. Rich, “L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women,” Int. J. Sport Nutr., 2000.
[28] M. Pooyandjoo, M. Nouhi, S. Shab-Bidar, K. Djafarian, and A. Olyaeemanesh, “The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials,” Obesity Reviews. 2016.
[29] F. B. Del Vecchio, V. S. Coswig, and L. M. Galliano, “Comment on ‘The effect of (l-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials,’” Obesity Reviews. 2017.
[30] C. Brandsch and K. Eder, “Effect of L-carnitine on weight loss and body composition of rats fed a hypocaloric diet,” Ann. Nutr. Metab., 2002.
[31] S. A. Melton et al., “L-carnitine supplementation does not promote weight loss in ovariectomized rats despite endurance exercise,” Int. J. Vitam. Nutr. Res., 2005.
[32] S. A. Center, K. L. Warner, J. F. Randolph, G. D. Sunvold, and J. R. Vickers, “Influence of dietary supplementation with L-carnitine on metabolic rate, fatty acid oxidation, body condition, and weight loss in overweight cats,” Am. J. Vet. Res., vol. 73, no. 7, pp. 1002–1015, 2012.
[33] Rebouche CJ. Carnitine. In: Modern Nutrition in Health and Disease, 9th Edition (edited by Shils ME, Olson JA, Shike M, Ross, AC). Lippincott Williams and Wilkins, New York, 1999, pp. 505-12.)

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