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Created for Greatist by the experts at Healthline. Read more

Last week your trainer hyped it as a workout recovery supplement. Then yesterday your co-worker raved about its fat-torching prowess. Rumor has it L-carnitine is a fat-burning, brain-boosting, performance-enhancing machine of a supplement.

But is it all it’s cracked up to be? Here are the details on L-carnitine.

If the name has you craving some juicy carne, you’re actually on the right track. L-carnitine is an amino acid derivative found in meat and animal products. Lucky for the vegans in the house, our bodies can also make it.

Whether you know it or not, you’re already familiar with L-carnitine. Your body relies on it every day. It’s responsible for fast-tracking fatty acids to your mitochondria, which burn the fat into energy. L-carnitine is basically the low-key conveyor belt sending your fat to the incinerator.

Some signs you’re deficient include:

  • decreased muscle tone or weak muscles
  • fatigue
  • irritability
  • symptoms of low blood sugar

These symptoms are similar to those of many other conditions, so talk to your healthcare provider before you jump on the supplement train.

The carnitine squad

There are several types of carnitine. L-carnitine kinda steals the spotlight since it’s the one in red meat and most supplements.

Meet the others:

  • D-carnitine. If L-carnitine is a fat-busting superhero, D-carnitine is its lazier twin. This inactive form might even restrict your body’s capacity to absorb more useful members of the carnitine family.
  • Acetyl-L-carnitine. Called ALC for short, this is the carnitine voted most likely to boost your brain power. The jury’s still out, but some research suggests it’s a good supplement for folks with neurodegenerative diseases like Alzheimer’s disease or Parkinson’s disease.
  • Propionyl-L-carnitine. If you’re dealing with circulation issues — anything from high blood pressure to erectile dysfunction — this is the carnitine for you. One study suggests it improves blood flow by increasing nitric oxide levels.
  • L-carnitine L-tartrate. Scientific evidence behind this common sports supplement is mixed. Some studies have shown that it speeds up muscle recovery, while others suggest it won’t do much to improve performance.

Bottom line:

ALC and L-carnitine are probably your best bets for a general supplement. But it’s also important to take a look at the different types in relation to your #goals.

Here’s what going down in your body RN

Almost all the L-carnitine in your body is stored in your muscles. The rest is chillin’ in your liver and bloodstream.

Right now your L-carnitine stores are busy keeping your mitochondria, aka your cells’ engines, fueled up. And since amino acids play a lot of roles, L-carnitine also picks up toxins and dumps them outside the cell walls. What a gem.

Bottom line:

L-carnitine lives in your muscles, where it shovels fatty acids into cells so they can be burned for energy. Your body makes L-carnitine, but you can boost your level through food or supplements.

Popping L-carnitine might sound like a pretty convenient way drop a little weight. But let’s keep it 100: Sure, L-carnitine is responsible for shoveling fatty acids into the furnace, but that’s just a teeny, tiny part of the metabolic process.

Despite claims from supplement companies, there just isn’t much medical evidence of L-carnitine’s weight loss superpowers.

Here’s what we know:

  • A 30-day study of 32 fat cats (yes, really) revealed that the kitties who took L-carnitine supplements had a dramatically higher resting energy expenditure (REE) and fat-burning capacity than the cats who didn’t get any. But in the end, the supplemented cats didn’t lose more weight than the others.
  • In a review of nine studies of people with obesity, researchers found that participants taking L-carnitine lost about 2.9 more pounds (1.3 more kilograms) than those who didn’t.
  • While L-carnitine supplements certainly won’t hurt your efforts to slim down, burning fat at the cellular level won’t make a difference without diet and exercise changes.

If you’re generally healthy, you probably already produce enough L-carnitine. But your biological clock wreaks havoc on more than baby-making and crow’s feet. Age can cut into your L-carnitine stores (so can diabetes and genetic conditions).

Studies on animals have suggested that L-carnitine can boost function in aging brains and possibly protect brain cells from damage.

Unfortunately, there isn’t much research yet on whether taking L-carnitine boosts brain power in younger, healthier people.

Let’s start with the good news: A 2013 review found that L-carnitine helped heart attack patients recover quickly. Since all the carnitines prefer to do their work inside muscle tissue, it makes sense that their presence is good for the heart.

But that same year, a study in mice found that L-carnitine in red meat might increase levels of trimethylamine-N-oxide (TMAO), which could cause clogged arteries.

What gives? A 2004 review of older medical research suggested that L-carnitine does the most for people who’ve already had a heart attack. The jury’s still out on exactly how it could help or harm healthy hearts.

Some research says L-carnitine supports workout #goals in the long term. Typically, L-carnitine is a slow burn. Don’t expect it to kick in overnight like caffeine or creatine. Stick with it and you might be running harder, better, faster, stronger in a few months.

On the flip side, a small study of professional athletes found that those who received 3 to 4 grams of L-carnitine immediately before a workout had better endurance.

Here’s how L-carnitine might improve your workouts over the long haul:

  • Endurance. It could help your blood flow and keep your heart rate down during intense exercise.
  • Muscle soreness. A 1996 study suggested that L-carnitine could reduce delayed-onset muscle soreness (aka DOMS).
  • Oxygen supply. A 2005 study on mice found that L-carnitine might speed up red blood cell production, which keeps oxygen flowing freely to the muscles.

Living with type 2 diabetes takes a whole lotta discipline. But there’s evidence that taking L-carnitine might alleviate some symptoms and risks.

Some research suggests acetyl-L-carnitine (ALC) dials down nerve pain and weakness caused by type 2 diabetes. A 2005 study suggested L-carnitine supplements could also lower blood sugar.

There isn’t much new research on links between type 2 diabetes and L-carnitine (weight loss studies get all the love, amiright?). But the bottom line is that if you’re dosing properly and checking with your doctor, L-carnitine is way more likely to help than to hurt.

L-carnitine is technically FDA-approved for just one use: treating carnitine deficiency. But doses of less than 3 grams a day seem safe for pretty much anyone. Taking too much (2 to 3 grams, depending on your body) can cause mild side effects, including:

  • nausea
  • stomach cramps
  • “fishy” body odor

And, as we mentioned, a 2013 study in mice found that L-carnitine in red meat might contribute to clogged arteries, although more research is needed.

tl;dr

More medical studies are needed, but up to 2 grams a day seems safe for most people. One animal study suggested that L-carnitine supplements could raise your risk of blocked arteries.

There’s no “one size fits most” answer for whether or not you should add a bottle of L-carnitine to your medicine cabinet.

Technically, your body can whip up L-carnitine without help, thank you very much. The main things to consider are your diet and whether your body is healthy enough to create what it needs.

The folks most likely to benefit from supplementation:

  • Vegetarians and vegans have a higher risk of L-carnitine deficiency since they don’t eat animal products.
  • Older adults might benefit from L-carnitine supplements since research shows your levels go down as you get older.
  • People with cirrhosis and kidney disease often have low L-carnitine levels. A supplement can help with their overall wellness.

If you still wanna give L-carnitine a whirl, remember to research the specific carnitine type that’s right for your goals. Chatting with your doctor isn’t a bad idea either.

Most people supplement with 500 to 2,000 milligrams of L-carnitine per day. Two grams (2,000 milligrams) seems to be the sweet spot for long-term effectiveness without health risks.

Pill-popping isn’t the only way to give yourself a little L-carnitine love. You can find it in foods, liquids, powders, and even injections.

While the best way to score nutrients is through diet and a healthy lifestyle, supplements can help. If you’re concerned about mixing meds, it’s always a good idea to check with your doctor.

Meat and dairy

Your body absorbs L-carnitine from food sources more quickly than from supplements. Sneak in some L-carnitine with a 3-ounce serving (about the size of your palm) of these meats:

  • Beef: 81 milligrams
  • Pork: 24 milligrams
  • Fish: 5 milligrams
  • Chicken: 3 milligrams

Meat is your best bet, but other animal products deliver itty-bitty doses of L-carnitine too:

  • Ice cream (½ cup): 3 milligrams
  • Cheddar cheese (2 ounces): 2 milligrams
  • Milk (8 ounces): 8 milligrams

Liquid

Mix a concentrated liquid supplement into your morning glass of water or OJ if you’re not a fan of swallowing pills. Bonus: You can try ALL the flavors! Start slow, with a 1,000-milligram dose per day.

Cost is the main drawback to liquid supplements. You’ll get more bang for your buck with powder or pill forms.

Powder

Powdered L-carnitine supplements work well for those who already whip up a protein shake or smoothie in the morning. Add a scoop (1,000 milligrams) along with your collagen or protein powder.

There’s not much difference in cost between powder and pills, so pick whatever strikes your fancy.

IV

Injections and IV doses of L-carnitine are best left up to the pros. In a 2014 study of people who had an L-carnitine deficiency, switching from pills to IV therapy had a positive effect on cholesterol levels.

If you think your body is L-carnitine deficient, it’s best to talk to your healthcare provider about treatment options and sources.

Pills

Most medical research on humans taking L-carnitine has involved pills, so sticking to this supplement form gives you the highest chance of getting good results. Vegetarian capsules are available, so it’s a #win for those who prefer their L-carnitine without the carne.

L-carnitine is known as a fat-burner because that’s what it does on the cellular level. Studies on leveraging that for weight loss have been mixed.

Of all the different carnitine types, L-carnitine and acetyl-L-carnitine show the most promise. There’s evidence that these forms are good for your brain and heart and even for disease prevention.

Supplements are a good idea for people with naturally low L-carnitine levels: older adults, vegans, and vegetarians. But it’s best to chat with your doctor before taking any new supplement.