Brad Murphy

Supplement companies have become L-Carnitine pushers.

It’s gotten to the point where I’m rolling my eyes reading something like, “our product contains a full clinical dose to melt fat and send your energy levels through the roof”.

When that starts to happen, I feel the need to write an article on the subject to help you wade through the industry’s swamp of exaggerated claims and twisted scientific interpretation.

So, here it is: everything you need to know about L-Carnitine (and its variations). What it can and cannot do for you, how much you should take, what products to look out for, and what to avoid.

There are several forms of L-Carnitine supplement (or supplements containing L-carnitine) , depending on how the compound is paired with another, to maximize different biological effects.

They include:

1. L-Carnitine
2. Acetyl-L-Carnitine (ALCAR)
3. L-Carnitine L-Tartrate (LCLT)
4. Glycine Propionyl L-Carnitine (GPLC)

You may also see it written as:

• Acetylcarnitine
• Levocarnitine
• L-3-hydroxy trimethyl aminobutanoate (I mean, obviously, right)

L-Carnitine, in its various forms is promoted by supplement companies for the following benefits:

• Fat burning
• Physical/exercise performance
• Muscle growth
• Energy
• Cognitive function
• Anti-depressant
• Insulin sensitivity
• Cardio vascular health

It can be found in liquid and powder form, in fat-burners, diet pills and pre-workout powders.

I’ll cover all of that, but for now, let’s start with the basics.

What Is L-Carnitine?

L-Carnitine is most like a B vitamin, but it also acts a lot like an amino acid.

In fact, it’s formed from two amino acids: Lysine and Methionine within the liver and kidneys.

So, it looks, sounds and behaves like an amino acid, and for the sake of simplicity most people will refer to it as such.

Others label it a “vitamin-like” or even “amino-acid-like” compound.

Having been studied for nearly seven decades now, we know quite a lot about l-carnitine, but some of its effects still remain to be fully explained.

Being able to synthesize it endogenously, and obtain it from animal tissue, the omnivores amongst us are rarely deficient in L-Carnitine. However, because it is mostly found in meats (with a little absorbed from milk) vegans and vegetarians have less.

Vitamin C dependent enzymes, Vitamin B6, niacin and iron play a role in the synthesis of l-carnitine. Therefore, deficiencies in any of those can also be problematic for endogenous l-carnitine levels.

Biosynthesis of l-carnitine only accounts for about 25% of your daily requirement. The rest must come from food and milk.

There is also some debate as to how vegetarians who do not supplement l-carnitine seem to avoid a deficient state. Modern research suggests it could be a regulatory feedback mechanism that enhances bioavailability, increases biosynthesis and reduces urinary waste to mitigate the otherwise low intake.

One study showed that supplementation increased muscle and plasma l-carnitine concentration but did not improve/affect muscle performance/function or energy metabolism.

Our bodies can store about 20 grams of l-carnitine on average. Ninety-five percent of that is in our muscle tissue and heart, while the remainder is in circulation through our blood and post-production in the liver and kidneys.

Its absorption ratio is much higher from food (~70%) than it is from supplements (~16%), which might be because the lower doses in food are more readily absorbed than supplemental doses, which can be upwards of 1500mg per day.

Due to the massive difference in total dosage, however, you’ll still absorb a lot more from supplements than you will from food. This also means vegans, vegetarians, meat and dairy eaters are pretty much on a level playing field after supplementation.

It’s one of those ingredients that truly cannot be ingested from your diet in the quantities you can get in supplement form.

What Does L-Carnitine Do?

In layman’s terms: L-Carnitine transports fat through the otherwise impermeable inner mitochondrial membrane, where it can be burned (oxidized) for use as energy [source].

During Low-Intensity exercise, l-carnitine acts as the platform for an enzyme called CPT1 to transport long-chain fatty acids into the mitochondria of cells. The mitochondria – essentially our cellular power stations – can use these fatty acids as fuel for metabolic processes.

This movement through the membrane to the mitochondrial compartment of the cell is known as mitochondrial flux.

During High-Intensity exercise l-carnitine forms acetylcarnitine which maintains a pool of Coenzyme-A, essential for mitochondrial flux to continue.

Given the depletion of the free carnitine pool for the formation of acetylcarnitine, an increase in muscle carnitine content (from supplementation) would provide additional substrate for the fatty acid translocation to continue even longer.

This process allows for mitochondrial ATP (adenosine triphosphate) production and delays glycolysis/hydrolysis (carbs) driven ATP production.

In basic terms, l-carnitine provides a buffer which prolongs the use of fat as fuel rather than switching to carbohydrates.

Additionally, this would delay the production of lactic acid and thus reduce muscle acidosis and the fatiguing effect to performance.

The result is a lowered perception of effort/fatigue combined with additional fat-burning activity.

Increasing the provision of l-carnitine through muscle carnitine storage is therefore one of the main reasons for supplementation.

To sum up: L-Carnitine supplementation is primarily used for:

• increased fat burning during exercise
• reduced body fat mass accrual
• reduced fatigue during intense exercise
• enhanced fitness and physique parameters (due to increased exercise ability)

How Important Is L-Carnitine?

It’s essential.

Within populations that don’t get enough, people can enter a deficient state. Symptomatic of that deficiency, are few potential health risks:

• Early onset dementia
• Muscle atrophy/weakness
• Hepatic (liver) dysfunction
• Cardiomyopathy (diseased heart/cardiac tissue stiffening, scar tissue etc.)
• Skeletal muscle myopathy

The vast majority of people will never need to consider such health issue because so little is required and it is prevalent in a rounded diet. There is also that potential for a safety switch that alters absorption ratios to fix low intake.

As for the importance of l-carnitine supplementation – it depends on your dietary intake. If you live in a developed country and eat a diet that incorporates meat, you shouldn’t have a deficiency.

Like I said, first world vegetarians and vegans should think about supplementing, despite modern research showing that other mysterious regulators are at work to raise endogenous levels.

Some congenital defects or acquired damage to organic cation transporter mechanisms can lead to carnitine deficiencies and the aforementioned cardiomyopathy and skeletal muscle myopathy.

Regardless of the problems a deficiency can cause, it is still not classified as a vitamin or mineral because it can be biosynthesized to some degree from methionine and lysine.

It’s best described as “conditionally essential”, where under certain conditions it can cause a state of deficiency and disease and.

Aside from all of that, commercial supplements are, generally speaking, intended for the benefits I listed in the introduction, rather than for avoidance of a diseased state. This is because it has been found in some research to provide benefits at dosages far above those possible from dietary intake.

L-Carnitine for Muscle Growth and Fat Loss

I’d say that the heavily marketed claims of enhanced muscle growth and/or fat loss are the reasons most people have landed upon this article. If you’re one of them, then thanks for reading this far.

There are a lot more reported benefits of l-carnitine supplementation, and some of them feed into the muscle gain and weight loss effects. In which case, they will also be discussed here.

I’ll get to the other unrelated benefits later, but if you’re itching to know whether the money you put down on your pre-workout or fat-burner was well spent, then this section is for you.

The following studies highlight some very important information with respect to how l-carnitine works when you supplement it, what dosages are effective and under what conditions it is effective.

1989 Study on Elite Athletes

One of the larger studies on L-Carnitine was conducted back in 1989.

The scientists took 110 elite level athletes, including those that competed in rowing, kayak, canoe, swimming, weightlifting and long-distance running.

Subjects were given 1000 mg (1 gram) of l-carnitine per day for 3 weeks. They observed differences in athletic performances after a single dose and following the 3 week course.

Single doss increased the following parameters:

• Physical output
• Lipid metabolism
• Muscular function (as contraction force)
• Lactate accumulation (i.e. a reduction)

The full three week course improved the following parameters:

• Lipid metabolism
• Muscular potential
• VO2 max
• Behaviour
• Biological output

The scientists attributed the improvements to the increased transportation of fatty acids into the mitochondria of cells to be used as a fuel.

Basically, l-carnitine assists the process of fatty acid transport into the mitochondria (your cellular power engines) to be burned as fuel.

This has two major effects:

1. It increases the energy in muscle cells, thus allowing for greater power. Greater power output leads to enhanced overcompensation and muscular potential grows over time.
2. Fatty acids being taken from adipose tissue to be burned as fuel in mitochondrial cells reduces the fat which is stored and so reduces total body fat over time.

Drawback: The 1989 study was only 3 weeks in length. This is short by any supplement study’s standards if only because some of them only begin to have an effect after a few weeks of consistent use.

This didn’t appear to be a problem here as the scientists recorded some extremely positive results. As you will see, however, later studies were up to 24 weeks in total and involved more accurate measurement techniques.

Comparing Pre and Post Millennium L-Carnitine Studies

Those are some good results, but not all l-carnitine studies tell the same story. Some show little to know improvement in performance, while others still appear to find different benefits.

The latter could be due to the design of the study and of course what the scientists are measuring, but how can we explain the differences in studies that are essentially measuring the same thing?

In fact, the results from studies involving trained athletes, including resistance trained men, are pretty unreliable.

This might be in part due to unreliable testing and old methodologies. Perhaps comparing a 30 year old study to one conducted in the last few years is not fair because the quality of the two are probably not equal.

Continuing with that logic, studies conducted after the year 2000 do show, on the whole, that l-carnitine supplementation does have a positive impact on physical performance, fat metabolism, muscle recovery, fatigue and cognitive function.

One important, and likely correct, theory is to do with how l-carnitine is consumed. The studies you are going to learn about below are true game-changers in this respect.

In the case of the 2011 and 2013 studies below, the L-Carnitine was ingested along with a carbohydrate drink. This was thought, and thus proven to be, a reliable means of increasing muscle carnitine content via an insulin-mediated pathway.

Previous studies had not applied this methodology consistently, hence why the results had been inconsistent to that point. If l-carnitine was supplemented, it may not have gotten into the muscle tissue sufficiently to exert its benefits.

Groundbreaking Study with Humans – 2011

Chronic oral ingestion of l‐carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. Benjamin T. Wall et al. 2011. The Journal of Physiology.

Up until the 2011 study, everyone was still confused about l-carnitine. Results of previous studies had been inconsistent, and the study designs themselves weren’t always up to par.

The 2011 study aimed to enhance the study design and build upon findings from the past, which highlighted the effects l-carnitine supplementation can have on muscle and exercise performance.

From the work that came before their study, the scientists felt it was reasonable/logical to conclude that by increasing the muscle carnitine reservoir (storage) via supplementation, a person could positively affect their muscle fuel metabolism in a couple of ways.

The largest dynamic would be largely determined by the intensity level of exercise.

Together, there was a study objective, followed by three hypotheses:

Objective: Determine whether chronic L-Carnitine plus carbohydrate feeding (in healthy men) increased muscle carnitine content to the same degree as their previous lab studies.

Hypothesis 1: Increased muscle carnitine content would decrease glycogen usage and increase/sustain fatty acid usage as fuel during low intensity exercise.

Hypothesis 2: When carnitine switches to acetylcarnitine during high intensity exercise, increased muscle carnitine content would increase mitochondrial flux, and therefore ATP production, thus reducing anaerobic ATP production and the concomitant lactic acid/lactic acidosis.

Hypothesis 3: Those positive effects of increased muscle carnitine content would improve high intensity exercise performance.

The study lasted 24 weeks, and involved 14 healthy, male recreational athletes in their mid-twenties who engaged in triathlon training (run, bike, swim) 3 to 5 times per week.

Volunteers were tested before commencing the study’s experimental visits to determine their VO2max (maximum amount of oxygen an individual can use during a maximal output exercise session).

Their VO2max was tested again after the study to ensure no significant improvement in aerobic capacity had been made (meaning the supplemental protocol would be the cause of any significant change in performance).

The Experiment

Subjects visited the lab 3 times over the 24 weeks with 12 weeks between each. They exercised on a cycle ergometer for:

• 30 minutes at 50% max output, followed by
• 30 minutes at 80% max output, followed by
• 30 minutes of a work output performance test

The third 30 minute spell there is an “all out” performance test but where the cycling cadence is under the subject’s own control rather than a pre-determined percentage of VO2max to exhaustion.

The scientists had determined from previous studies that “volitional cycling cadence” for a fixed time was a better measure of endurance exercise performance.

The Study Supplementation Protocol

The fourteen men were split into two groups.

Important: Insulin stimulates the transport and uptake of carnitine into muscle, which is why a carbohydrate drink was used as the delivery method in this study.

1. Group 1: Consumed 80 grams of an orange flavoured carbohydrate drink (~600 calorie) twice per day for 168 days.*
2. Group 2: Consumed the same drink PLUS 2 grams (2000mg) of l-carnitine twice per day for 168 days.

*the first drink was taken at breakfast time and the second 4 hours later. Again, this was based on previous research which showed this to be a viable way to increase carnitine retention.

Samples and Analysis

At each of the three visits, several samples were taken from the subjects for analysis.

1. Blood samples for blood glucose, insulin and of course carnitine levels.
2. Muscle biopsies from the vastus lateralis (largest quad) at rest and within 5 seconds of finishing exercise, both at 50% and 80% VO2max (while they were still sat on ergometer) for free carnitine, acetylcarnitine, and long-chain acylcarnitine as well as ATP, phosphocreatine, creatine, lactate and glycogen

Let’s just talk about those muscle biopsies for a second.

Study write-ups discuss muscle biopsies with the usual detached/objective scientific voice, but they are an intense procedure for the subject.

A biopsy is the surgical removal of muscle tissue. In this instance, the researchers used the Bergstrom percutaneous needle method. Despite sounding rather mild, it still removes a chunk of muscle a few millimetres in cross section, and has to be taken deep enough to ensure 100% muscle tissue extraction.

With that in mind, remember that these med were subjected to 3 of these biopsies per visit, and two of them within 5 seconds of peddling on an ergometer. What’s more the second and third bioposies were done on the bike immediately before cycling for 30 minutes at 80% VO2max and 30 minutes at volitional max respectively.

It’s safe to say that these dudes are pretty incredible, and to do this for the advancement of sports science is honourable.

What I’m saying here is: if you ever meet anyone who’s been subjected to a muscle biopsy, or 9, then buy them a drink. We all benefit from the data that comes out of these studies, but not all of us get sliced up while doing an intense workout in the process.

Study Results

The results of the 2011 l-carnitine study can be summarized as follows:

1. The Carnitine group has no change in body mass over the 24 weeks, where the control group gained over 5 lbs.
2. Blood total carnitine concentrations were greater in Carnitine group after 12 and 24 weeks of supplementation.
3. Perceived exertion after the 24 week visit was lower in the Carnitine group compared to the control group
4. Muscle total carnitine content was 30% greater in the Carnitine group after 24 weeks compared to control.
5. Resting Free Carnitine trended to 30% greater in Carnitine group over control

The next sub-section is a continuation of the results, but merits some additional focus…

Significant Differences in Metabolic Response to Exercise Intensity

Following the low intensity exercise (50% VO2max) muscle glycogen content was 35% greater in the Carnitine group compared to control. This equated to 55% less glycogen being used during the exercise.

Also, free carnitine was 78% greater in the Carnitine group compared to control.

After high intensity exercise (80% VO2max) muscle glycogen was 71% greater in the Carnitine group over control. This was due to the reduction in glycogen usage during the low intensity exercise and so there was no difference in glycogen usage between groups after high intensity exercise.

However, muscle lactate content was 44% lower in the Carnitine group over control following the 80% VO2max cycling. This means of course that less lactic acid was produced during exercise, which in-turn means less anaerobic ATP production was required.

There was also a trend towards greater acetylcarnitine and free carnitine in the Carnitine group.

Work output performance exercise – the 3rd/last 30 minute exercise spell of “all out” volitional cycling – was found to be no different between groups until the 24 week visit.

At 24 weeks, the Carnitine group acheived 35% greater output compared to the control group. This was an 11% increase compared to the carnitine group’s baseline measured at the start of the study before the visits.

Takeaways from the 2011 Study

This was the first study that demonstrated a reliable method to increase muscle carnitine content, with the co-ingestion of a carbohydrate drink.

The increase of 21% is not small either.

Neither is the 55% less glycogen usage during low intensity exercise. To any endurance sport athletes out there, that result should get you pretty excited because it leaves more glycogen for the more intense efforts.

Also, for anyone who exercises in the low intensity range for fat loss, it should be even more exciting. The energy required to exercise must come from somewhere, and if more than half the glycogen is being used then it is coming from fat stores.

Another blinding result is the large difference in lactate production at high intensity exercise that l-carnitine supplementation appeared to facilitate compared to control.

While the control groups’ lactate production increased at both 12 and 24 weeks compared to baseline, the Carnitine groups increased initially at 12 weeks but then returned to baseline levels at 24 weeks.

Matching baseline might not sound amazing but bear in mind that the men’s glycogen stores were increasing. That increase caused the control group to use more glycogen and thus anaerobic respiration, which produced more lactate.

The Carnitine group at 24 weeks even reduced their lactate production from 12 weeks and saw a zero increase compared to week 0, despite a concomitant rise in glycogen storage.

This again means that more ATP is produced via mitochondrial membrane flux rather than through anaerobic respiration.

All of these advantages set the athletes up for a 35% greater output during the “all out” work output exercise.

What remained to be studied after this was the finding that body mass remained the same in the Carnitine group compared to a >5 lb increase in the control group, despite both groups taking on a calorie surplus from the drink.

There is a hint in the discussion of the 2011 study that it could again be down to the Carnitine supplementation and the upregulated fat metabolism it clearly causes, but they quite rightly don’t stray from the study’s findings.

L-Carnitine Prevents Body Fat Accumulation in Humans – 2013 Study

The follow up study that came in 2013 dealt with that body mass observation during the 2011 study, where the Control group added over 5 lbs on average, and the Carnitine group added no body mass despite all subjects consuming a calorie surplus.

Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans. Francis B. Stevens; Benjamin T. Wall et al. 2013. The Journal of Physiology.

So, while the 2011 study was exciting with respect to muscle carnitine content; physical performance and energy metabolism, the 2013 study took a closer look at the energy metabolism aspect.

Perhaps most importantly for a lot of people, the emphasis on body fat mass could tell them with more certainty as to whether l-carnitine was a viable weight loss supplement.

Let’s recap that 2011 body mass observation:

– L-Carnitine (at 2.7g/day) plus carbohydrates (at 160g/day) supplementation by the carnitine group prevented them gaining a 5 lb increase in body mass, that the control group (carbs only) experienced, after the first 12 weeks of study.

That observation is almost worthy of the following assumptions:

• The 5 lbs body mass was fat mass in the control group
• The L-Carnitine supplementation prevented the accumulation of that fat mass in the carnitine group

In the 2013 study, the scientists wanted to follow a carnitine + carbohydrate feeding program again, similar to the 2011 study.

Additionally, they decided to measure the expression of nearly 200 genes associated with carnitine and energy (fuel) metabolism in the subjects.

Gene expression would bolster the insight gained from the invasive scientific analysis alongside, plus that of the 2011 study.

Hypothesis: that any change of energy metabolism as a result of increased muscle carnitine content would occur alongside adaptations in expression of genes related to fuel use, mitochondrial function and insulin signalling.

Given the similarity of the study procedure, we should skip on ahead to the results.

Study (2013) Results

Again, just like the 2011 study, the control group put on weight after 12 weeks. The carnitine group did not.

The weight increase was entirely due to an accrual of body fat mass.

• Control group gained 4.2 lbs +/- 1.5 lbs of fat
• Carnitine group gained ZERO

Energy expenditure also increased over the 12 weeks in the Carnitine group, but not in the control group.

• Control group did not increase energy expenditure
• Carnitine group increased energy expenditure by 6% compared

Perhaps as important as this finding is that:

• Control group – the control group experienced a negative change in energy metabolism compared to their baseline readings at the start of the study
• Carnitine group – every member of the carnitine group experienced a positive change in energy expenditure compared to their baseline

This result is almost certainly down to the carnitine group’s increased metabolism of fat which trended to 10% compared to their baseline.

• Control group – no significant change in fat oxidation compared with baseline
• Carnitine group – trending to 10% increased in fat oxidation compared to baseline

Remember the enzyme CPT1 that I mentioned in the What Does L-Carnitine Do section?

Carnitine Palmitoyltransferase 1 (CPT1) is the enzyme derived from its substrate l-carnitine, and is responsible for the transfer of long-chain fatty acids through the mitochondrial membrane for oxidation.

These long-chain fatty acids arrive at the mitochondrial membrane attached to Coenzyme A (CoA), where CPT1 transfers the acyl group (including the fatty acid) to l-carnitine. This combination can then travel through the membrane to be oxidized.

The 2013 study showed the following:

• No change in maximal muscle CPT1 activity after 12 weeks in either group;
• however: Muscle total long chain acyl-CoA content at rest increased fourfold in the carnitine group compared to baseline AND the control group (who’s remained at baseline)

This 4 x carnitine content in the muscles is similar to when fuel metabolism switches to fat oxidation during rest periods from exercise where muscle carnitine stores are high.

However, the fact that CPT1 activity did not change counters the other findings of this study. The scientists themselves could not explain this, and determine that further research is required.

A possible explanation would be that CPT1 maximal activity is not solely determined by quantity of CPT1 protein but rather its capacity when dealing with a greater concentration of Acyl-CoA (which Carnitine content causes in the muscle).

Gene Expression

The most “enriched” functional pathways from the genetic testing were:

• Fatty Acid metabolism
• Insulin signalling
• PPAR signalling

All three of which are heavily involved in the processes of fat oxidation/metabolism, carbohydrate transport and triglyceride (more fat) metabolism respectively.

It certainly appears as though increased carnitine content can mitigate the negative effects of carbohydrate caloric surplus on insulin signalling.
Takeaways from the 2013 Study

Once again the advantages of increasing muscle carnitine content were shown with this study.

1. Over 4 lbs of body fat accrual experienced by the control group (just carbs) was completely avoided by the carnitine group after 12 weeks of supplementation and 20% increase in muscle carnitine content, all during carbohydrate caloric surplus.

2. Low intensity exercise energy expenditure increased by 6% in the carnitine group compared to zero in control, most likely due to additional fat oxidatiom.

3. Low intensity exercise fat oxidation increased in every subject of carnitine group, trending to 10% compared to baseline and markedly more than control.

4. Resting muscle long-chain acyl-CoA increased by 200% in carnitine group compared to baseline AND control. This is indicative of a switch to fat metabolism during rest periods. Additional carnitine content in muscles extends process.

5. Seventy three out of 187 genes measured increased expression in carnitine group.

The three genes that changed the most are critical for (a) insulin signalling; (b) PPAR signalling; and (c) fatty acid metabolism – all supported the hypothesis that chronic (long-term and consistent) muscle carnitine loading can improve energy metabolism.

In basic terms, increased muscle carnitine content can increase fat metabolism during low intensity exercise and prevent fat mass storage during carbohydrate caloric surplus.

The potential for increased/improved insulin sensitivity can also be inferred.

What Are the Additional Benefits of L-Carnitine Supplementation?

The above studies focused on physical performance at both high and low intensity, energy metabolism (inc. a genetic context), fat loss and insulin health.

Perhaps the 3 most exciting benefits from those studies are that L-Carnitine supplementation:

1. Triggers significantly increased fat burning as fuel over muscle glycogen

2. Prevents fat mass accrual even in carbohydrate calorie surplus

3. Reduces perception of fatigue significantly during intense exercise

…but that’s not where the reported benefits of l-carnitine supplementation end.

Other benefits you’ll be interested in are as follows:

4. Increased Blood Flow and Muscle Pumps via Nitric Oxide production and protection (Atalay Guzel N et al)[https://europepmc.org/abstract/med/25289711]

5. Increased Testosterone by increasing androgen receptor density – and upregulating them in muscle – tissue (Kraemer, William J. et al)
6. Decreased Muscle Soreness/Damage
7. Improved Recovery
8. Improved Sexual Health
9. Acetyl-L-Carnitine (ALCAR) improves Cognitive Function

How To Take L-Carnitine

L-Carnitine, irrespective of the specific form, should be consumed with carbohydrates. It’s advantageous to consume protein alongside your l-carnitine and carbs as well.

Without a relatively high insulin spike your l-carnitine supplement is much less effective.

You shouldn’t worry about this though because, as the researchers have shown, it improves your insulin function anyway, favours fat burning and prevents carbohydrate driven weight gain.

Furthermore, it’s wise to split your total daily amount of l-carnitine into two separate servings.

1. 1st serving at breakfast
2. 2nd serving with post-workout meal/shake OR with lunch on non-workout days

Next, I’ll talk specific numbers on dosage and carbohydrate/protein feeding.

Recommended Dosages of Various L-Carnitine Supplements

The following are the average recommended doses of the different forms of l-carnitine supplements:

L-Carnitine

Take 3 grams (3000mg) of straight L-Carnitine a day, following the feeding guidelines

Acetyl-L-Carnitine (ALCAR)

Acetyl-l-Carnitine has a higher absorption ratio from the intestines compared to the other forms and thus can be found in capsule supplements and taken at lower doses.

Up to 1500mg of ALCAR split into a couple of doses over the course of the day should be enough.

L-Carnitine L-Tartrate (LCLT)

This form of l-carnitine is typically used as a performance enhancer and for improving overall power output during a workout. You’ll find it in pre-workout supplements, but it’s still best taken with a source of carbohydrates.

Daily doses of 1-4 grams (1000 to 4000mg) are common but I’d aim for the upper end of that as with straight l-carnitine and take 3000mg of LCLT.

Glycine Propionyl L-Carnitine (GPLC)

Similar to l-carnitine and LCLT you should take about 3000mg in total over the course of the day. This form is best for enhancing blood flow and getting a decent muscle pump.

For muscle pumps, it works in combination with other ingredients that boost NO like L-Citrulline.

Protein and Carbohydrate Requirements with L-Carnitine

As previously discussed, l-carnitine enters the muscle tissue via insulin-mediated transport and so consuming carbohydrates with your l-carnitine supplement is recommended.

The research subjects discussed in previous sections of this article took 80 grams of carbohydrates twice a day with the l-carnitine.

I defintiely recommend splitting your daily total of l-carnitine into two separate servings.

Carbs: I would suggest around 30 to 50 grams of carbohydrates would be enough to spike insulin sufficiently for the process to take effect. Do this for both the morning dose and early afternoon/post-workout dose of l-carnitine

Protein: At the same time, a portion of protein should be eaten. Lean protein at about 30 grams should be sufficient (20-40g range is fine). Post workout protein scoops sizes are usually about this much

Your carbs and proteins can be in the form of food at breakfast and lunch or as a well-formulated carbohydrate supplement designed for post-workout use.

Personally I eat a breakfast that includes both of those macros at those rough quantities for my first serving of l-carnitine. For my second serving I either take a combined protein/carb post-workout shake with it, or eat lunch on my non-workout days.

Acetylcarnitine may be taken in between meals as it has a better absorption ratio in the absence of carbohydrate.

Does L-Carnitine Cause Side Effects?

The recommended doses above should cause no side effects. I suggest splitting the daily total into two servings because large single servings can cause a bit of an upset stomach.

With larger than recommended doses, a person might experience nausea, vomiting, diarrhea, stomach pain…similar abdominal and intestinal issues that can occur with high doses of BCAAs, Creatine or Beta Alanine etc.

Some people are Carnitine non-responders according to evidence but this isn’t a side effect as much as it is a lack of benefit.

In rare cases of people with seizure disorders using l-carnitine, supplementation can trigger a seizure. Also people suffering with uremia (urea in blood from abnormal protein metabolism) might experience muscle weakness. Obviously, those people should avoid l-carnitine supplements.

Closing Remarks on L-Carnitine

L-Carnitine is a trending ingredient in the supplement industry, and it appears from reviewing some key research that the excitement is valid.

One thing to remember is that L-Carnitine does not appear to have acute effects. In fact, regardless of the 1989 study observations that single doses improved performance across the board, later studies have reliably shown that it requires chronic supplementation to work.

What do they mean by chronic supplementation? – I believe indefinite would be the appropriate term.

The 2011 study that I believe blazed the trail for the present day hype over l-carnitine followed a 24 week daily dosing protocol.

Given that’s as good as six months, it’s safe to say you won’t benefit from cycling l-carnitine on and off.

Some bodybuilders tend to only use it on a cut cycle, which makes sense considering the prevention of carbohydrate driven mass gain is not conducive to adding bulk.

If you work within basic linear progression cycles and enjoy the bulk/strength/cut routine then by all means, stop using l-carnitine when you are aiming for maximum hypertrophy.

Many of you however are probably looking for a supplement that can consistently help you lose weight in the form of fat mass, boost your energy levels, increase your power output and improve your physique.

If that describes you fairly well then l-carnitine looks like a winner. The prevention of fat storage during carb-caloric surplus should be enough for a lot of people to jump on this supplement. The improvements in energy expenditure and insulin sensitivity almost feel like bonuses in comparison.

On the rare occasion that a supplement appears to work for healthy, exercising humans, in terms of fat burning and performance enhancement, it’s a good idea to grab some and see how it works for you.

L-Carnitine is one of those supplements.