Your Expert Guide to L-Carnitine

L-Carnitine supplements have been popular for years now and remain some of the most frequently purchased products on the market.

There’s also a lot of outrageous claims attributed to supplementing with L-Carnitine. Some will say it will magically burn body fat, while others maintain it’s completely and utterly useless.

What’s the truth?

As with most things, it lies in between.

In this article, we'll discuss precisely what L-carnitine is, what it does in the body, and what benefits may result from its use.

Let’s get started!

What is L-Carnitine?

Carnitine is an amino acid derivative that’s naturally synthesized within the body and is also found in many other animal-based foods.

It is created in the liver and kidneys from the essential amino acids lysine and methionine, and it is primarily stored (~98%) in the cardiac and skeletal muscles, where it plays an essential role in energy production.

Smaller concentrations of carnitine can also be found in the brain as well as sperm.

On average, the human body contains roughly 20–25 g of L-carnitine, and the average daily intake of carnitine through the diet is 100–300 mg. <1>

L-carnitine was isolated for the first time from muscle tissue in 1905, and its structure was established in 1927. Initially, it was perceived to be a “vitamin-like” compound and was referred to as vitamin BT. <1>

Typically, a healthy individual can synthesize sufficient carnitine to keep up with the demands of energy production in the body.

However, some individuals (such as preterm infants or those with genetic defects), cannot create enough to keep up the body’s energy needs, which means carnitine becomes a conditionally essential nutrient and individuals must pair close attention to their dietary intake of carnitine or begin to use carnitine supplements.

Furthermore, the use of certain antibiotics can decrease carnitine absorption or increase its excretion. <2,4>

Lastly, since L-carnitine synthesis also requires sufficient amounts of iron, vitamin B6, vitamin C, and niacin, being deficient in any one of these nutrients will impair L-carnitine synthesis and potentially result in muscle fatigue (due to insufficient energy production). <1>

What Does L-Carnitine Do?

The primary function of carnitine is to shuttle fatty acids, particularly long-chain fatty acids (those fatty acids with 13-21 carbon atoms), to the inner mitochondrial membrane so that they can be oxidized ("burned") to generate adenosine triphosphate (ATP) -- the cellular "currency" of energy production.

(Note that L-carnitine does this fatty acid shuttling both during exercise and at rest.)

On their own, long-chain fatty acids cannot enter the mitochondria. Carnitine acts as a sort of biological “taxi” that picks up fatty acids from the cytoplasm of the cell and shuttles them into the mitochondria.

In addition to shuttling fatty acids into the mitochondria for energy production, carnitine also shuttles potentially toxic compounds out of the mitochondria, which protect the availability of free Coenzyme A (CoA).

In case you weren’t aware, Coenzyme A plays significant roles in energy production as it is involved in the synthesis and oxidation (“burning”) of fatty acids, as well as the oxidation of pyruvate in the citric acid cycle (a.k.a. the TCA or Krebs cycle).

In other words, not only does carnitine play a vital role in energy production, but it also helps preserve and protect the cell as well.

Dietary Sources of L-Carnitine

In addition to being naturally produced within our bodies, carnitine can also be obtained

The word carnitine is derived from the Latin carnus (meaning "flesh") because it was first discovered in meat. As you might expect, animal-based proteins, including meat, fish, poultry, and dairy, are some of the best food sources to obtain the essential fat burning compound.

Generally speaking, the darker (or “redder”) the particular cut of meat is, the higher the carnitine concentration there is present in the meat.

Regarding dairy products, carnitine typically only is present in the whey protein portion of dairy -- which is just yet another reason to continue enjoying your whey protein shakes!

Here’s a table listing some common foods along with the individual carnitine contents <1>

Food	Milligrams (mg)
Beefsteak, cooked, 4 ounces	56–162
Ground beef, cooked, 4 ounces	87–99
Milk, whole, 1 cup	8
Codfish, cooked, 4 ounces	4–7
Chicken breast, cooked, 4 ounces	3–5
Ice cream, ½ cup	3
Cheddar cheese, 2 ounces	2
Whole wheat bread, 2 slices	0.2
Asparagus, cooked, ½ cup	0.1

What Are the Different Types of Carnitine Supplements?

Carnitine exists in two forms: D-carnitine and L-carnitine.

By and large, the only form of carnitine you’ll find used in supplements is the L-form.

The reason for this is that D-carnitine is not biologically active, and it may be toxic since it inhibits the activity of L-carnitine. <3>

Now, L-carnitine supplements can be further divided as a number of different forms of L-carnitine have surfaced over the years.

Let’s now look at the differences between the various forms of L-carnitine, beginning with the favorite of biohackers and nootropic nerds:

Acetyl L-Carnitine (ALCAR)

Acetyl L-carnitine is an acetylated form of L-carnitine that is naturally produced by the body and can be taken as a dietary supplement. The reason this form of carnitine is used as a nootropic is that ALCAR more readily crosses the blood-brain barrier than other forms of L-carnitine supplements due to the addition of an acetyl group (-COCH3).

ALCAR has been heavily investigated for its potential to aid in the treatment of Alzheimer’s disease. <5>

In case you weren't aware, individuals with Alzheimer's have reduced carnitine stores in the body as well as a significant decrease in the production of acetylcholine, the "learning neurotransmitter."

ALCAR may help combat the progression of Alzheimer’s in two ways.

First, it supplies the body with an extremely bioavailable form of carnitine, but more importantly, it also provides a valuable acetyl group, which forms the "backbone" of acetylcholine.

Furthermore, ALCAR also acts as a powerful antioxidant and neuroprotective agent in the brain by preventing and repairing damage caused by free radicals that harm brain cells <6,7>.

ALCAR also enhances the neural network by strengthening and reinforcing nerves and signal receptors. And, it’s even been documented to help protect the brain against the harmful effects of drinking alcohol. <8>

As if that’s not enough, acetyl l-carnitine also has been noted in research to help alleviate mental fatigue, improve learning, boost cognition, and heighten mood.< 9,10,11,12>

L-Carnitine L-Tartrate (LCLT)

L-Carnitine L-Tartrate is formed by combining a molecule of carnitine to a molecule of tartaric acid (tartrate).

It's at times called the "athlete's carnitine" due to several studies which note that supplementing with it offers benefits for those active individuals who like to get after it in the weight room.

For starters, l-carnitine l-tartrate supplementation has been noted to improve the rate of fat oxidation in skeletal muscle, which may increase the amount of fat burned during exercise. <13,14>

This should, in theory, spare glycogen stores during lower intensity efforts and save them for later in the workout when high-intensity, explosive movements are performed. Additional studies also note that these altered energy kinetics may help reduce an athlete’s perception of effort as well as increase their work output. <26>

Additional research suggests that supplementing with l-carnitine l-tartrate may enhance muscle building and reduce soreness by increasing androgen receptor density. <15>

Increasing androgen receptor density should enhance cellular uptake of testosterone, the main "muscle building" hormone of the body. Additionally, LCLT also elevates luteinizing hormone, a hormone that stimulates Leydig cells to generate testosterone.

Based on these effects, researchers note that supplementation with L-Carnitine L-tartrate may improve recovery due to reductions in exercise-induced muscle tissue damage. <13,16>

Finally, LCLT supplementation may also support metabolic health as research notes that supplementing with LCLT (3 g/day) for two weeks favorably impacts glucose homeostasis and insulin release in healthy lean and overweight/obese males during a 2-hour oral glucose test. <21>

Glycine Propionyl L-Carnitine (GPLC)

Glycine Propionyl L-Carnitine (GPLC) is a propionyl ester of carnitine that tacks on an additional glycine component. It is metabolized into L-carnitine and propionyl coenzyme A.

While other forms of carnitine are supplemented primarily for their nootropic or exercise recovery benefits, GPLC is typically used as a nitric oxide booster, due to some research noting it may increase blood levels of nitrate/nitrite. <17,18>

GPLC isn't just for pumps, though; some other research has noted it may enhance anaerobic work capacity and overall performance. <19>

Another study using GPLC noted it helped increase power output by 15% higher and decreased post-exercise blood lactic acid by 15-16% compared to placebo. <20>

Propionyl L-Carnitine (PLCAR)

The final form of l-carnitine supplement you’re likely to encounter is PLCAR, which stands for Propionyl L-Carnitine (PLCAR).

Similar to the other forms of carnitine discussed thus far, PLCAR supports energy production (via increasing ATP). Still, it also has been documented to offer several health benefits, too.

Namely, propionyl l-carnitine has been shown to help decrease inflammation and improve cardiovascular function. <22>

Various studies note that propionyl l-carnitine may be useful in the treatment of certain cardiovascular disorders, such as congestive heart failure or angina pectoris. <23,24,25>

Should I Supplement with L-Carnitine?

Sufficient levels of L-Carnitine are needed to oxidize fatty acids for energy, which is why many people believe that supplementing with l-carnitine is necessary to lose body fat.

However, as we explained above, your average fitness buff who trains regularly and eats an otherwise healthy diet that includes animal proteins should have no problem synthesizing enough carnitine to satisfy energy demands.

Now, if you are vegan, vegetarian, or elderly, you may need to supplement with L-carnitine. The reason for this is that (in the case of elderly individuals), carnitine production declines with age, and, in the case of vegans and vegetarians, their diets are low in L-carnitine as well as the precursors and supporting nutrients needed to create l-carnitine endogenously. <1,29>

Studies have shown that vegetarians have lower levels of L-Carnitine in their blood.<1>

Many individuals will say that carnitine supplementation is needed to lose fat. While it's true that carnitine is necessary to oxidize fatty acids for energy, unless you are deficient in carnitine, supplementing with it may not directly help you lose weight, especially if you're not in a calorie deficit.

Additional studies show that boosting carnitine levels above normal levels doesn’t lead to greater fat burning.

So, unless your diet is lacking in carnitine (or its necessary cofactors), don’t expect much direct fat loss from supplementing with carnitine.

However, L-Carnitine may indirectly benefit fat loss and muscle gain due to its effects on soreness and recovery.

Essentially, the less soreness you experience after a workout, the more quickly you can recover from it, which allows you to train more frequently and with greater intensity, burning more calories and lifting more weight, thereby facilitating your weight loss or muscle gain goals.

Do I Need to Cycle L-Carnitine?

Based on the current body of evidence, cycling L-carnitine does not seem to be needed. It is non-hormonal and naturally occurring in the body as well as many foods common to the diet.

The Bottom Line on Carnitine

L-carnitine supplements are incredibly popular, though not for many of the reasons they should be.

Unless you’re deficient in carnitine, supplementing with L-carnitine won’t directly help you lose fat or gain muscle. However, it may help you feel less sore and recover more quickly from your workouts, thereby allowing you to train harder and more frequently, ultimately making greater progress than you otherwise could.

If you’re looking to supplement with L-Carnitine, SteelFit ®recommends Carnipure®.

Carnipure® is a special grade of L-Carnitine developed by the Swiss manufacturer Lonza.

Lonza has been a leader in L-carnitine research for over 30 years and has conducted several human studies in collaboration with universities and research centers to investigate the potential benefits of supplementing with Carnipure® L-Carnitine.

SteelFit® utilizes only Carnipure® L-Carnitine in its Liquid L-Carnitine 3000, Steel Burn™.

References

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