L-Carnitine: Benefits, Side Effects & Dosage

Amino acids are all the rage these days. People pop them like pez to build muscle, increase energy, burn fat, improve focus, treat illness — the list goes on. The body uses these tiny compounds to make proteins, peptides and to facilitate gene expression, among other crucial, life-giving things (x). In short, you can’t live without them. And L-carnitine (or simply carnitine), even though it isn’t exactly an amino acid, is just as important.

What Is L-Carnitine?

Carnitine is actually made out of two amino acids — lysine and methionine — like the child of proud parents. Carnitine has the important job of helping the mitochondria in the cells make energy (x). It does this by carrying long-chain fatty acids into your mitochondria to be burned for fuel. In science-people language, the mitochondria “oxidize” these fatty acids. For example, think of the sooty stoker shoveling coal into a steam engine. That’s carnitine putting fuel into your cells’ engine rooms so that you can get up out of bed in the morning and go about your day. Mom and Dad (lysine and methionine) would be so proud!

Assuming you’re healthy, your body makes enough carnitine on its own, thanks to help from your liver and kidneys producing lysine and methionine. But if you want to do a bit more heavy lifting, you can take carnitine supplements or eat carnitine-rich foods. Carnitine supplements are available in powders and capsules (x). And if you’re the house chef, stock up on that ground beef, codfish or cheddar cheese (x). When it’s BBQ season, opt for the beef steak, an incredibly rich natural source of carnitine. Vegans and vegetarians should consider carnitine supplements since cooked vegetables contain much less natural carnitine.

Carnitine Deficiency

Can you be carnitine deficient? Yes, you can. In fact, according to the Office of Dietary Supplements over at the National Institutes of Health (NIH), there are two types of carnitine deficiencies — primary and secondary (x). The first is a “genetic disorder of the cellular carnitine-transporter system.” In other words, your mitochondria have a harder time using fats to burn energy (x). Symptoms include skeletal-muscle weakness and abnormally low blood sugar.

The NIH classifies secondary carnitine deficiency as the result of other disorders, like chronic renal failure, or “particular conditions […] that reduce carnitine absorption or increase its excretion” (x). But can supplementing carnitine treat these rare conditions? The NIH acknowledges scientific agreement that they can.

We want to know more about how this tiny compound can benefit our health. Let’s have a look at what research has to say about it.

L-Carnitine Benefits

Weight Loss

A study published in the Asia Pacific Journal of Clinical Nutrition found that carnitine reduced obesity in mice fed a high-fat diet (x). Researchers split a number of mice into three groups. For 12 weeks they fed one group a normal diet, another a high-fat diet and the last a high-fat diet with 0.5 percent carnitine supplementation included.

After 12 weeks, researchers found that the mice they gave a carnitine supplement to had lower body weight and energy intake than the mice they fed the normal high-fat diet to. In addition, carnitine-supplemented mice showed lower weights in white fat tissue and lower levels of serum leptin, a hormone that tells you when you’ve had enough to eat.

These researchers concluded that “L-carnitine supplementation diminished the risk of obesity caused by a high-fat diet.” Seems promising!

On Diabetes

The same study looked at the effects of carnitine in diabetic mice. Researchers gave 24 rats diabetes by injecting them with streptozotocin, which is poisonous to insulin-producing pancreatic cells. Finally, they injected carnitine into each rat every other day for four weeks and found that carnitine increased insulin-like growth factors (IGFs) in each rat.

IGFs are growth hormones that, similar to insulin, can decrease blood-sugar levels (x). These IGFs were largely absent in the rats before carnitine injections began. Researchers determined that carnitine modulated IGFs and was able to restore them to normal levels in the diabetic rats.

On Exercise Performance

Chapter 21 in the book Food Components to Enhance Performance: An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations states that carnitine enhances exercise performance in several ways (x).

  • Stimulating fatty-acid oxidization: Carnitine carries fatty acids into mitochondria so that they can be oxidized for energy.
  • Stimulating the use of carbohydrates and amino acids: In addition to carrying fatty acids into the mitochondria, carnitine also plays taxi to the compound acetyl-CoA, which helps metabolize fatty acids, amino acids and glucose, increasing its role as the energy-producing mitochondria’s henchperson.
  • Preventing lactate buildup: During exercise, muscles produce lactate, which can accumulate and cause acidosis. Acidosis is what causes muscle aches and pains and that unpleasant burn feeling.

Carnitine may help boost your energy while helping your muscles fight off that nasty burn. You may exercise longer and feel less tired afterward.

Heart Health

Cardiac ischemia is a condition where the heart loses its supply of blood and oxygen. After this happens, tissues may become damaged once blood flow suddenly returns. This is called reperfusion injury.

Researchers in a study published in the Journal of Huazhong University of Science and Technology found that carnitine helped protect heart tissue in animal subjects during reperfusion (x). They determined that carnitine did this by preventing energy loss and keeping up antioxidant activity in these animal’s hearts when they lost their supplies of blood and oxygen.

Brain Function

A study published in Neurochemistry International claims that an ester form of carnitine, acetyl-L-carnitine (ALCAR), has an effect on the brain, “protects against neurotoxic insults” and may treat depression (x).

Researchers in this study supplemented mice with ALCAR for 25 days to examine differences in “cerebral energy” and neurotransmitter metabolism. They found that ALCAR increased the neurotransmitters noradrenaline in the hippocampi (a tiny region in the center of the brain) and serotonin in the cortexes (the largest region of the brain) of these mice.

Noradrenaline is responsible for giving strength to the contractions of skeletal muscles and the heart. And serotonin is responsible for making you feel happy and well.

L-Carnitine Benefits

Food Sources of L-Carnitine

Taking carnitine supplements is incredibly easy. If you lead a busy life, throw some powder into your smoothie before you dash out the door (x). Or, you can pop a capsule with your coffee and bagel as you catch the subway to work. But if you prefer to savor your time in the kitchen, or if you’re a chef by hobby, you can consciously increase the carnitine in your diet by cooking with these whole foods (x):

  • Cooked beef steak (4 ounces): 56–162 milligrams
  • Cooked ground beef (4 ounces): 87–99 milligrams
  • Whole milk (1 cup): 8 milligrams
  • Cooked codfish (4 ounces): 4–7 milligrams
  • Cooked chicken breast (4 ounces): 3–5 milligrams
  • Ice cream (1/2 cup): 3 milligrams
  • Cheddar cheese (2 ounces): 2 milligrams
  • Whole-wheat bread (2 slices): 0.2 milligram
  • Cooked asparagus (1/2 cup): 0.1 milligram

As for vegetarians and vegans, cooked asparagus will get old, very fast. Try supplementing carnitine if you want to increase your bodily amounts. That said, you can also try cooking with more legumes (beans, peas and lentils) and soybeans to consume more lysine (x). And you can consume more methionine by eating more whole-grain products (x).

Remember — lysine and methionine are carnitine’s constituents.

L-Carnitine Dosage and Side Effects


Although many supplements are safe to take, exercising caution is your best defense against unwanted side effects. Your first defense should always be talking to your doctor before taking new supplements. They will determine what supplements are right for you and how much you should be taking daily.

Your next defense is to follow dose instructions on the packaging of the supplement you’re taking. Start with small doses first before gradually increasing them.

Side Effects

Research published in the journal Nature Medicine suggests that taking too much supplemental carnitine over a long period of time may contribute to atherosclerosis (x). This is a condition where plaque buildup in the arteries causes them to narrow and harden.

How does this happen? In the gut, intestinal microbiota break down carnitine into a substance called trimethylamine-N-oxide (TMAO). TMAO is proatherogenic, which means it promotes fatty-plaque buildup in the arteries. It does this by suppressing reverse cholesterol transport, a mechanism the body uses to deliver excess cholesterol to the liver for redistribution to other parts of the body or for removal from the body via the gallbladder (x).

To us, this research says one thing — watch how much carnitine you supplement. Use it to reap its benefits, and don’t go over the top. Ultimately, the health-sciences community needs to conduct more research into this supplement to determine whatever other negative effects it might have on the body.

The Bottom Line

Carnitine is a close friend to the amino-acid family. It’s made from lysine and methionine and is responsible for carrying fatty acids into the mitochondria to be oxidized for energy. Your body makes enough of it on its own, assuming you’re healthy. But if you want to increase the amount of it in your body, you can supplement it (available as powders or capsules) or you can eat foods rich in it — red meats, chicken and fish.

Recent research supports its positive effects not only on weight loss, but on diabetes, heart health, brain health and exercise performance as well. It’s also associated with very few side effects. If you plan to supplement carnitine, take small doses first before gradually increasing them. Always talk to your doctor before taking supplements, and always follow dose guidelines on supplement packaging.

Author: BulkSupplements Staff