|It won't spare you the sweat, but carnitine could make it even more worthwhile by ramping up the anabolic and shutting down the catabolic signals.|
Still, the evidence has always been inconclusive to say the least
Despite the fact that the concomitantly elevated post-workout luteinizing hormone levels (+19%) Kreamer et al. observed would tell you that the testosterone that would have been necessary to activate those receptors was already on its way, I have never considered this study as convincing evidence of the anabolic prowess of l-carnitine. Plus, let's be honest, differences in whatever serum markers in response to an acute bout of resistance training have failed us way too often, not to look at studies like these with appropriate skepticism.
|Do you remember the Ratames study from 2005? The one that showed that high volume training lowers the no. of androgen receptors on the trained muscles? This certainly makes l-carnitine sound like the perfect addition to high volume routines, right? (learn more)|
Now, the soon-to-be-published paper by Janine Keller and her colleagues from the University of Giessen (Germany) certainly qualifies as part of the evidence we simply cannot ignore, when we are looking for evidence in support of the theory that l-carnitine could be an overlooked muscle builder or repartitioning agent.
After all, their observation of decreased levels of the proteolytic (=catabolic) MuRF1 protein, as well as the ubiquitin-protein conjugates, which are increased in catabolic states such as starvation and atrophy denervation (cf. Wing. 1995) , alone, would signify that l-carnitine could make a valuable addition to everybody's supplementation regimen.
Lower catabolism + increased anabolism = ???
There is more, however, the addition of 1250 mg L-carnitine/kg to a basally "low carnitine" vegetarian diet also led to significant increases in systemic IGF-1 concentrations in plasma and a local increase in the activity of the PI3K/Akt/FoXO-1 signalling pathway (see figure 1)
|Figure 1: IGF-1 mRNA and serum levels, as well as the muscle specific expression and phosphorylation (ph) Akt, mTOR & co after four weeks on the low or high carnitine diets (Keller. 2013)|
"And you are telling me that works in humans, as well? "
What's the best form of carnitine to take to elicit these effects: I knew you would ask this, so I react to two facebook questions by adding this red box willingly admitting that I just cannot tell you what the best form of carnitine is. There simply is no study that would compare e.g. acetyl-l-carnitine (ALCAR) and l-carnitine l-tartrate (LCLT) in a scenario that would be relevant to the above question. What I can tell you though, is that it appears as if you were better off with LCLT than with ALCAR, if your goal is to top off your intra-muscular carnitine levels. That being said, even normal creatine can do that - you will just have to take more of it. If you are looking for more information you can check out the part of the Amino Acids for Super Humans Series that's dealing with "the carnitines", here.In this context it does yet also have to be mentioned that the effects of l-carnitine are at least in part species specific. How we know that? Well, in contrast to the said study by Basquets et al. the provision of an carnitine to piglets (Keller. 2012) did not only reduce the MuRF-1 expression, but also the level of its likewise catabolic E3 ligase cousin atrogin-1.
"It has been shown that myofibrillar proteins, like myosin light chain proteins are the main targets of MuRF1for ubiquitination. Thus, carnitine might suppress particularly the degradation of myofibrillar proteins, which under physiological conditions comprise around 60% of total muscle proteins. In contrast to MuRF1, atrogin-1 tags primarily proteins for degradation which are important for controlling protein synthesis and myoblast differentiation, like myogenic factor MyoD, myogenin and the eukaryotic initiation factor of protein synthesis eIF3-f." (Keller. 2013)With pigs usually being a superior model of the human physiology, this would suggest that the anti-catabolic effects l-carnitine could have on humans are probably more, not less pronounced than those that were observed in previous rodent studies.
Bottom line: Irrespective of the absence of human data on the IGF-1 boosting effects from non-HIV patients - or even better in training scenarios - it would warrant future studies if an adequate amount of carnitine in the diet can exert beneficial effects in non-obese human beings. For the "sedentary", or let's rather say non-exercised rodents in the study at hand, the latter was a mere fat loss effect - despite the elevations in p-AKT, m-TOR, IGF-1 and the overall more "anabolic" state the rodents were in their lean body mass was not increased compared to their peers on the low carnitine diet.
|"Just another set!" ... "I don't know man, we've already pumped away 100,000kg today... do you really believe that's productive, I mean, yeah, we are cuttin', but still" ...learn what this dialog is all about and whether and if / when "another set" is / isn't a good idea (read more)|
So what's the verdict then? I guess, I will leave the final words to Burke et al. who reviewed the usefulness of carnitine as an ergogenic aid in one of the first installments of the "A-Z Supplement Review" in the British Journal of Sports Medicine and wrote "future work with l-carnitine may also find some useful outcomes" (Burke. 2009) - needless, to say that the SuppVersity is going to be the place, where you will read about it first ;-)
- Broquist HP. Carnitine. In Shils ME, Olson JA, Shike M (eds): "Modern Nutrition in Health and Disease." Malvern, PA: Lea & Febiger, 1994. 459– 465.
- Burke LM, Castell LM, Stear SJ, Rogers PJ, Blomstrand E, Gurr S, Mitchell N, Stephens FB, Greenhaff PL. BJSM reviews: A-Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 4. Br J Sports Med. 2009 Dec;43(14):1088-90.
- Busquets S, Serpe R, Toledo M, Betancourt A, Marmonti E, Orpí M, Pin F, Capdevila E, Madeddu C, López-Soriano FJ, Mantovani G, Macciò A, Argilés JM: l-Carnitine: An adequate supplement for a multi-targeted anti-wasting therapy in cancer. Clin Nutr. 2012;31:889–895.
- Di Marzio L, Moretti S, D'Alò S, Zazzeroni F, Marcellini S, Smacchia C, Alesse E, Cifone MG, De Simone C. Acetyl-L-carnitine administration increases insulin-like growth factor 1 levels in asymptomatic HIV-1-infected subjects: correlation with its suppressive effect on lymphocyte apoptosis and ceramide generation. Clin Immunol. 1999 Jul;92(1):103-10.
- Glass DJ: Signalling pathways that mediate skeletal muscle hypertrophy and atrophy. Nat Cell Biol. 2003; 5:87–90 .
- Kraemer WJ, Spiering BA, Volek JS, Ratamess NA, Sharman MJ, Rubin MR, French DN, Silvestre R, Hatfield DL, Van Heest JL, Vingren JL, Judelson DA, Deschenes MR, Maresh CM. Androgenic responses to resistance exercise: effects of feeding and L-carnitine. Med Sci Sports Exerc. 2006 Jul;38(7):1288-96.
- Keller J, Ringseis R, Koc A, Lukas I, Kluge H, Eder K: Supplementation with l-carnitine downregulates genes of the ubiquitin proteasome system in the skeletal muscle and liver of piglets. Animal. 2012;6:70–78.
- Keller J, Couturie A, Haferkamp M, Most E, Eder K. Supplementation of carnitine leads to an activation of the IGF-1/PI3K/Akt signalling pathway and down regulates the E3 ligase MuRF1 in skeletal muscle of rats. Nutrition & Metabolism. 2013; 10:28.
- Lösel D, Rehfeldt C. Effects of l-carnitine supplementation to suckling piglets on carcass and meat quality at market age. Animal. 2013 Mar 11:1-8.
- Salama AF, Kasem SM, Tousson E, Elsisy MK. Protective role of L-carnitine and vitamin E on the testis of atherosclerotic rats. Toxicol Ind Health. 2013 Feb 13.
- Viganò A, Mora S, Brambilla P, Schneider L, Merlo M, Monti LD, Manzoni P. Impaired growth hormone secretion correlates with visceral adiposity in highly active antiretroviral treated HIV-infected adolescents. AIDS. 2003 Jul 4;17(10):1435-41.
- Wing SS, Haas AL, Goldberg AL. Increase in ubiquitin-protein conjugates concomitant with the increase in proteolysis in rat skeletal muscle during starvation and atrophy denervation. Biochem J. 1995 May 1;307 ( Pt 3):639-45.