What is L-Carnitine.
Carnitine is a conditionally essential natural chemical derived from amino acids, though we can make it within our bodies and gain it from our diet some people may not be getting enough. Since Carnitine is formed from lysine and methionine as long as you are eating a complete protein source at a high enough level there shouldn't be any issue here.
What does it do.
Carnitine has two main roles within the body. A part of its structure carries long chain fatty acids into the mitochondria of cell to be used as fuel, the second role is in waste removal from the mitochondria preventing toxic build up within the cell. For this reaoson Carnitine is concentrated within the skeletal and cardiac muscles [1,2].
Beyond simple nutrient shuttling Carnitine has been shown to play a role in androgen receptor uptake after resistance training and feeding [3,4].
Forms of Carnitine.
Acetyl L-carnitine: Sometimes refereed to as ALCAR, this form is bound to acetyl acid as it more readily allows Carnitine to pass the blood brain barrier as well as the gut [5]
D-carnitine: This type is the optical isomer (mirror image) of L-carnitine. It is toxic to the body, as it may inhibit the absorption of other forms of Carnitine. [6]
L-carnitine L-tartrate: This form of Carnitine is bound to Tartrate acid which is essentially an inert acid used only to stabilise the Carnitine allowing to to be more bio available and not break down as fast in the gut. This is the form that this analysis will focus on, as it is most widely used in the research I have read.
Propionyl-L-carnitine: This form, while similar to the Acetyl form can pass the blood brain easier than plain Carnitine, however research suggests that it may be more effect at what it does [8]
L-carnitine: This Carnitine is what is produced in the body, though taking orally it will break down with poor absorption rates, which is what the bound compounds seek to avoid. [9]
Before we continue I would like to reiterate that this analysis will focus on the L-carnitine L-tartrate (LCLT) and not the other compounds. This is because they have slightly differing mechanisms of action that are beyond the scope of this breakdown, if there is appetite further breakdowns on individual forms then I may go into those as well.
Practical application
Androgen Receptor up-regulation.
Relatively recent research has shown LCTL supplementation has been able to increase the amount of androgen receptors in muscles at rest before exercise as well as increasing AR count post exercise with the addition of a post workout meal consisting of all three macro nutrients against placebo. [3] The increased number and density of androgen receptors in muscles allows Testosterone to then bind to the AR pathing the way to faster recovery [10].
Speculation
It isn't clear how effective this is in the long term for muscle building and strength as these studies simply do not exist. Though we do know for certain that AR expression plays a fundamental role in resistance training-induced muscle hypertrophy. [11]
Because we know the association between AR content and muscle size it would stand to reason that LCTL AR upregulating ability should promote muscle hypertrophy in resistance trained individuals.
There is of-course the caveat that again we don't know much about the ratio of free Testosterone binding to these new free ARs, which would directly effect how effective this supplement is in building muscle.
Note
Interestingly one study measuring IGF-1 (growth hormone) post exercise with LCTL supplementation showed a marked increase against control [4] The study suggests this is another mechanism of action to explain the increased recovery seen with LCTL.
Fat loss.
As LCTL shuttles fats into the cell to be used as energy over sugars it has been long suggested and advertised as a fat burning agent but the research here has been sketchy and a bit light on the ground. The best argument for LCTL as a fat burning agent is when used in conjunction with some form of medium to low exertion cardio [11] through its lipid oxidisation and glycogen sparing abilities.
potential application:
If you want take LCTL 30 mins before low intensity steady state (LISS) cardio, for example, walking. Though LCTL supplementation alone will not be as effective or at all without a calorie deficit.
Endurance.
Supplementing at 3-4g of LCTL researchers found 26 candidate professional American footballers had a significant increase in exercise performance that titrated up in intensity before exhaustion [15], however another study on endurance trained athletes running marathon showed no benefit at all [16].
potential application:
Take LCTL for HIT style workouts, but forget it for endurance style training.
Recovery
Supplementing LCTL at 3-4g again has showed that immediately after exercise blood markers indicated decrease oxidative stress post exercise [17]. The reenforces the idea that LCTL promotes recovery post resistance or high intensity style workouts. Another study supplementing at 2g with resistance trained individuals showed similar results in muscle soreness and stress [18]
potential application:
Again take LCTL for HIT style workouts, but forget it for endurance style training.
Cardiovascular health
It has been shown that supplementing with Carnitine has had some positive effect in all cause mortality, decreasing it by 27% as well as positive outcomes for those who have gone through heart attacks.[19]
Another study reenforces with showing supplementation may decrease early death from heart related issues [20]
Note
Doses where not stated in these studies and they report that further testing on the efficacy and safety of LCTL supplementation is needed. If you decide to take LCTL for cardiovascular health for existing conditions I would advice first consulting with your Doctor.
Mental Health
Mental decline in the elderly has been shown to be alleviated in one studying showing all markers from, mental fatigue to physical fatigue to be reduced in this supplementing with 2g of LCTL. [21] Another again conducted on the elderly reduced symptoms of Alzheimer's dementia. [22] It is suggested that due to the nutrient shuttling capability of LCTL the energy efficiency is increased thus reducing the mental fatigue and other symptoms.
Practical application:
It is impossible to say at this time if LCTL is effective as a nootropic for otherwise cognitively healthy people wanting a cognitive boost. This meta analysis suggests that until better research is conducted LCTL is probably not worth perusing as a cognitive enhancer [23]
Infertility in males
The Carnitine content in seminal fluid is directly correlated to the amount and mobility of sperm [24,25] suggesting that it may be beneficial in treating infertility in men. Several studies have been shown to increase sperm count, mobility and quality on men treated for infertility. I will link 4 studies that all dosed between 2-3g for several months, each of these showed positive markers on the mens sperm quality [26,27,28,29] Thankfully the quality of evidence here is pretty compelling and for once, isn't clouded in poor, or lack of, research.
Dosing
Dosing is all over the shot in the litriture for LCTL, ranging from .5g to 6g per day. This can be explained by its poor bioavailability when taken orally and lack of consistently clear research.
Based on there studies I have linked here showing LCTL to be beneficial taking 2-6g per day before some form of exercise seems to be the most efficacious.
Side effects
It has been reported that doses up to 3g has the potential to cause nausea, vomiting, abdominal cramps, diarrhoea, and a “fishy” body odour. though these finings are very inconsistent and very poorly understood.
It has been reported that LCTL causes an increase in TMAO in the gut that has been linked to cardiovascular disease. [30]
Note
Gut TMAO production can be decreased though the supplementation of allicin [31] which can either be supplemented with raw, crushed garlic or as a extracted powder. There is also the potential of DMB from Balsamic Vinegar and Olive Oil to reduce TMAO levels [32]
Carnitine can also be injected IM which will bypass the gut and TMAO production. However, at least in my country it is not possible to get injectable Carnitine for recreational use.
The bottom line
LCTL has been around the block for a long time with research covering many different avenues, unfortunately a lot of it is inconstant and not particularly clear. This is a painfully consistent message with many compounds in the fitness industry. Regardless, the initial research is promising and may well end up being an effective compound for muscle growth.
Anecdotally I have recently been supplementing with 4g of LCTL for the past 8 weeks alongside the rest of my supplement stack and have noticed fairly significant trend in relation to my body weight and gym performance while on a 250-500 cal deficit, I still have a few months supply left but if the trend continues I will be replacing my stock and continuing. Personally I would recommend the product to those wanting to make the most out of their training.
Parting Words
This breakdown was a fairly research intense one, so I do hope you enjoyed it. to reiterate if further analysis on the other forms of Carnitine is wanted then I can go into detail on those in a later breakdown.
As always I am open to suggestions in what you want to see next, if non are forth coming then I will default to Betaine.
I will happily answer any questions you may have below.
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