Ask The Supplement Guru: Is Carnitine Safe?
Let me start by stating that carnitine is not dangerous and is a very safe and effective supplement. The recent confusion about carnitine arises from a new study that reported a possible association between carnitine and atherocsclerosis. But before I get into the details of this flawed study, let's first take a closer look at carnitine and what it does in your body.
L-carnitine, or just carnitine (the "L" refers to the configuration of the carnitine molecule that is biologically active) is often referred to as an amino acid, but it is not a true amino acid. Carnitine is an amino acid-like compound that is made in the body from the amino acids lysine and methionine.
Its name is derived from the Greek word for flesh or meat, carnus. Not so coincidentally, it's abundant in red meat and dairy products, but it can also be found in various nuts, grains, and green vegetables. Your body also naturally produces carnitine, and if you're chronically deficient, you struggle to use fat as a fuel. This can lead to muscle weakness, stunted growth, and an enlarged liver, among many serious problems.
One of the main roles that carnitine plays in the body is in assisting the transport of fat into the mitochondria of cells, such as muscle cells. It is here in the mitochondria where the fat is burned away as fuel. This is why carnitine is a popular ingredient in fat burners. Research confirms that supplementing with carnitine increases the amount of fat burned, particularly during exercise. This enhances fat loss and also boosts muscle endurance by sparing muscle glycogen.
Carnitine has also been found to improve blood flow by increasing nitric oxide production. This relaxes the smooth muscles of the blood vessels, causing them to widen, allowing more blood to flow through. This can further promote muscle endurance through better deliver of nutrients and oxygen to working muscles, along with helping to improve recovery after exercise.
With all these benefits, carnitine sounds like quite a beneficial supplement. So you are likely confused with why the New York Times and many other newspapers are suddenly reporting on carnitine as if it's going to kill you. They even have a study to support this sensationalism! But let's take a closer look at that study.
It was published in the journal Nature Medicine by researchers at the Cleveland Clinic. They reported that the intestines contain microbiota that can convert carnitine into trimethylamine-N-oxide (TMAO), an organic compound which may promote atherosclerosis. They also reported that the consumption of carnitine increased TMAO levels in red meat eaters, but not in vegans, due to a difference in gut microbes between omnivores and vegans or vegetarians.
So what's the problem? Among the major flaws in this study, the researchers based many of their conclusions about TMAO on research done in mice. So we don't truly know whether or not TMAO actually causes cardiovascular disease in humans. Another issue is the fact that the human component of their study consisted of only six people: one vegan and five meat-eaters. Six people is not even close to being enough subjects to draw conclusions.
Additionally, after reading the study, I'm left wondering about the health of these meat-eating subjects. Did they exercise regularly? Did they eat a healthy diet? These factors can all dramatically impact a person's gut microbiota. In short, this study is weak at best, so take it with a shaker cup-sized grain of salt.
The Cleveland Clinic study isn't the only major carnitine study to come out recently. A brand new meta-analysis study published in the journal Mayo Clinic Proceedings analyzed 13 different studies on the effects of carnitine and cardiovascular disease. The researchers reported that carnitine is actually helpful for fighting against cardiovascular disease, not contributing to it. You read that right.
More specifically, they found that supplementing with carnitine reduced all-cause mortality by almost 30 percent, reduced heart arrhythmias by 65 percent, and reduced symptoms of angina by 40 percent. Additionally, they noted research showing that carnitine helps to prevent atherosclerosis, not lead to it.
It's easy enough to explain how the Cleveland Clinic study got such big headlines. Once one prominent paper decided to run with the latest dose of doom and gloom, dozens of others seemingly had no choice. I'd be happy if the more positive study got the same level treatment, but I'm not holding my breath.
If you're taking carnitine now, feel safe to continue taking it for better endurance during workouts, greater muscle growth and strength gains, and improved fat loss. Based on the study in Mayo Clinic Proceedings, it may also offer a host of other health benefits that include enhanced cardiovascular health.
Because L-carnitine requires insulin to be taken up into the muscle, I suggest that you take about 2-3 grams of either L-carnitine or L-carnitine L-tartrate (Carnipure), either with high carb meals or a protein shake. Good times for this are in the morning with your first meal, and with your pre- and post-workout meals.
- Natali, A., et al. Effects of acute hypercarnitinemia during increased fatty substrate oxidation in man. Metabolism 42(5):594-600, 1993.
- Muller, D. M., et al. Effects of oral L-carnitine supplementation on in vivo long-chain fatty acid oxidation in healthy adults. Metabolism 51(11):1389-91, 2002.
- Wutzke, K. D. and Lorenz, H. The effect of l-carnitine on fat oxidation, protein turnover, and body composition in slightly overweight subjects. Metabolism 53(8):1002-6, 2004.
- Bacurau, R. F., et al. Does exercise training interfere with the effects of L-carnitine supplementation? Nutrition 19(4):337-41, 2003.
- Stephens, F. B., et al. New insights concerning the role of carnitine in the regulation of fuel metabolism in skeletal muscle. J Physiol 581(2): 431-444, 2007.
- Huang, A. and Owen, K. Role of supplementary L-carnitine in exercise and exercise recovery. Med Sport Sci 59:135-42, 2012.
- Koeth, R. A., et al. Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. In press, 2013.
- DiNicolantonio, J. J., et al. L-Carnitine in the Secondary Prevention of Cardiovascular Disease: Systematic Review and Meta-analysis. Mayo Clinic Proceedings. In press, 2013.
- Sayed-Ahmed, M. M., et al. L-carnitine prevents the progression of atherosclerotic lesions in hypercholesterolaemic rabbits. Pharmacol Res 44(3):235-42, 2001.
- Stephens, F. B., et al. Insulin stimulates L-carnitine accumulation in human skeletal muscle. FASEB J 20(2):377-9, 2006.
- Stephens, F. B., et al. Carbohydrate ingestion augments L-carnitine retention in humans. J Appl Physiol 102: 1065-1070, 2007.
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Great article and critique. I was skeptical when a client told me about this and it made them afraid when they noticed carnitine as a part of their whey shake. The media can sensationalize and create panic from one article without considering others in the process.
AH! References, references, references! Listen up boys and girls: he didn't get a PhD by not doing homework!
Next time a teacher asks did you cite your sources think of this example!
I think this relates to most things in life....Moderation. Whether it's too much carnitine or too much caffeine...it can have some serious effects on some people and not so much on others. Thanks for this information!
If L-Carnitine supposedly burns fat and increases muscle endurance during workouts, Why does Jim Stoppani have someone taking Acetyl-Carnitine 30-60 minutes before one works out and L-Carnitine 30-60 minutes after the workout?
I would say that carnitine can be absorbed in many different forms. That and after exercise your body experiences short/long duration EPOC (excess post-exercise oxygen consumption) where your body still facilitates energy stores to recover.
Acetyl will still provide many of the benefits that regular carnitine will. Acetyl can also affect the brain for mental focus, clarity, memory, etc. If I had to give an educated guess, that's probably why. You want to head to be as focused as your body is when you want to get the most out of a workout.
I take liquid L-Carnitine with a meal, usually dinner as the bottle directions say "take with a meal" and do not take on an empty stomach. However this article and others say to take it pre-workout...? Suggestions?? Comments??
Yeah, you can take it pre-workout - just not by itself. Take it with a pre-workout snack or protein shake. Jim says above it's best to take it with a higher carb meal like breakfast or a pre/post workout shake because L-carnitine requires insulin to be absorbed by the muscles.
Great article. Next, I'd really liek an unbiased article on the benefits and dangers of D-Aspartic acid. It seems tremendously beneficial in T support but is also lnked to nreve disorders like Huntington's disease. I'd like to try it, but am unwilling until I know more about the risks.
Thank you so much for writing this article! I have encountered so many people who try to convince me that supplements are bad for you because of something they "heard" or read in a dumb magazine without actually doing the research themselves in credible scientific journals. This article is a BOOOYAA to all people like that!
The study suggesting that carnitine found in meat/beef create TMAO which leads to heart diseases but the study failed to include food which is naturally high in TMAO such as peas, sea food/fish, cauliflower- in other words this study is nothing but bogus-Check out Dr. Mercola for even better understanding of this "failed" study(btw I am vegetarian)
i just saw this report too on cbs news and scoffed at it, literally, it ****** me off, CBS News
said they(the researcher and the clinic) followed the diet of 3500 people or something to that effect over a certain course of time and based their results on this as well...anyhow, i loved that you covered this, Jim....I am so glad cause this is the first place I go to to see if anyone is talking about things...you're my mentor!
Lol, who don't work in the fitness industry. Having read some of the papers Jim has a point that this study contradicts a lot of other good studies and it may well lead to nothing. Is a bit annoying hearing people say the study is 'highly flawed' and 'bogus' though, was a pretty thorough publication in one of the worlds most respected journals.
Ahh, a bit of rationality. Gotta agree with you guys (pogue, j19b90m). Stoppani can write whatever he wants, I could come up with similar flaws in 90% of references he uses in his articles, not to mention conflict of interest, his arguments are thin, but will satisfy layman, and that was the point. This article was written simply to keep people buying those supplements. Mayo clinic proceedings has pathetic impact factor, comparing it to Natural Medicine is... lol. Sorry, for my English.