What are L-Carnitine Benefits and Side Effects?

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You may have heard about l-carnitine if you are in the health and fitness industry, which is where it is most widely used and talked about. It’s  an amino acid that’s very much known in these fields for its performance enhancing effects and fat burning qualities.

But, let’s take a look at the science behind the hype to see what are l-carnintine benefits and side effects. And, more importantly, if it’s something that may be suitable for you and your own specific needs.

So, what Exactly is L-Carnitine?

This ‘vitamin type’, non essential amino acid is related to the B-vitamin family, and is used in the body for transporting dietary fat into the mitrochondria. These mitrochondria are organelles that act a bit like a digestive system, taking nutrients from the blood and breaking them down to create energy.

L-carnitine is produced in the liver and kidneys by the other amino acids methionine and lysine. It is then stored in the muscles, heart, brain and sperm.

Food Sources of L-Carnitine

This amino acid is mostly found in animal products, especially red meat (56-162mg per serving). But, is also found at much lower levels in food sources such as poultry, fish, seafood (3-7mg) and dairy products (3-8mg). 

What about vegan diets?

mixed pulses

L-Carnitine can be found in plant sources such as tempeh, avocados and peanuts, but unfortunately not at very high levels. But, the good news is that this doesn’t seem to make a difference, as deficiency is rare, even in strict vegans.

Deficiency is rare because the body can produce its own l-carnitine in the liver and kidneys from the other amino acids, methionine and lysine. All of which are abundant in plant foods such as nuts, seeds, lentils, wholegrains, tempeh, quinoa, seitan, black beans and soya milk. All the foods vegans usually eat in abundance!

Therefore, deficiency is usually only found in those who have kidney and liver function problems, both of which can prevent you from producing your own adequate supply.

The Science Behind L-Carnitine

Commonly used in the fitness world for its ability to stimulate the release of growth hormone and help reduce body fat, l-carnitine also transports fatty acids into cells where they can be oxidised and used for fuel. This cellular reaction happens both when you are at rest, and during exercise itself.

According to studies, it is most effective whilst you are engaging in very intense exercise.

Without this amino acid, it is very hard for fats to be burned as fuel. And, this is ultimately what most exercisers and body builders are trying to achieve.

L-Carnitine Benefits and Side Effects


toned abdominal muscles

The University of Nottingham gave athletes in their trial 2g of l-cartinine, along with 80g of high G.I. carbohydrate. They took the supplement as soon as they w0ke up before breakfast, then again 4 hours later.

 It was confirmed that when trialed over a period of 24 weeks they burned 55% less glycogen from muscles, whilst at the same time increasing ability to burn fat by 55%.

This means l-carnitine is a supplement that could actually help the body to burn fat more efficiently.

And, as it also has the ability to help your body burn less glycogen, it means you will have more stamina to train for longer. Hence the reason why you can burn more fat and build more muscle.


L- carnitine can play a role in helping aid you to train harder and for longer periods. Both of which will ultimately lead to better results and higher fitness levels. This PubMed study on a group of professional soccer players found that supplementation with this particular amino acid helped them to play for longer and lowered their time to exhaustion.

This suggests that l-carnitine could potentially be a good supplement to try if you are an endurance athlete. Or, a long distance cycler, swimmer or runner.


Another 9 studies were conducted in randomised trials on a group of mostly obese and older patients.

It was found that l-carnitine supplementation resulted in a weight loss of an extra 1.33kg, and a decrease of BMI (body mass index) of 0.07 kg compared to the placebo group.

However, other studies have not had the same results, so it’s a bit of a mixed bag as to whether you should seriously consider l-carnitine as a weight loss supplement.

What is interesting though, is the fact that the trials that seem more effective seem to be on the already obese and older groups. This makes l-carnitine more likely to be effective if you fall into these ranges when used alongside a structured health and fitness program.


Sore leg muscles

L-carnitine has been shown to significantly fasten the recovery period and reduce damage done to the muscles during exercise when taken at doses of 1-2 grams per day. It also decreases the muscle soreness you can feel for days after a hard workout.

Muscle soreness could ultimately lead to you missing sessions. Or, not putting your all in when you need to due to pain. This could be especially detrimental if you are a professional athlete. Fortunately, l-carnitine may help negate this.

Fasten recovery with the plant based diet!

Another great way to help alleviate muscle soreness and fatigue and fasten up recovery time, is to eat a much more whole food plant based diet. This healthier lifestyle may help lower chronic inflammation in the body.

Many plant based athletes are noticing much less muscle soreness, aches and pains after exercise, along with enhanced performance.

L-carnitine will also give you that extra edge during your training sessions by increasing blood flow and delivering more nutrients to the muscles when you need it most.


Another great side effect of l-carnitine is higher testosterone levels, which in turn can boost muscle growth and strength. It’s all due to the fact that l-carnitine increases androgen receptors and boosts your hormonal response to exercise.

Don’t worry, you can still take this supplement without worrying about turning into Arnold Schwarzenegger if that’s what you don’t want. The side effects will be subtle, and the muscles will be more toned rather than bulky. 

However, if you would like to get bigger and more muscly then that’s awesome. L-carnitine can help you achieve this, alongside other amino acid supplements and a high protein diet.


L-carnitine boosts brain cells and helps to keep your brain from aging. Its powerful antioxidant effects can help to slow down the aging process. This helps to keep the brain and heart youthful and firing on all cylinders, thus potentially lowering your risk of age related degenerative diseases.

And, this slowing down of the aging process does not just mean on the inside, but the outside too!

You can enhance these effects even further will a diet filled with other anti aging antioxidants for best results.

Dosage, when, and how to take L-Carnitine

Clickable Image

Depending on your weight, size, and fitness regime you should take between 500 and 3,000 mg per day (that’s equivalent to 0.5-3 grams).

The best time to take this supplement is with a meal that contains both carbohydrates and protein.

This also applies to some of the other forms of this amino acid such as propionyl-l-carnitine and l-carnintine l- tartrate.

On the other hand, the form of l-carnitine called acetyl-l-carnitine is more readily absorbed by the muscles, brain and intestines when taken alone and without food. The acetyl type of l-carnitine works well when taken along with other fat burners such as green tea, healthy green superfoods, or these other effective metabolism boosting foods

Best Form of L-Carnitine to Take

Acetyl-l-carnitine (the most common type used in the fitness industry) is more readily absorbed by the muscles, brain and intestines. Acetyl is able to cross the blood-brain barrier for the synthesis of acetylcholine (one of the brains primary neurotransmitters), and should be taken alone and without food.

Acetyl is also good for the support of the cardiovascular and nervous system, memory and brain power.

This form of l-carnitine helps you to burn fat for fuel just like regular l-carnitine, but is actually primarily used for its other benefits.

Straight up l-carnitine

Man drinking protein shake

This form (which is another popular form in the fitness world) supports weight loss, and also boosts the body’s ability to burn fat for fuel by mobilising fat from storage to be burnt as energy. This form should be taken with a high protein, high carbohydrate meal (or a high protein shake), and preferably after a workout. 

It’s worth noting that there are other primarily brain boosting forms of carnitine. These are Propionyl-l-carnitine and l-carnitine l-tartrate which should also be taken alongside food.

Can I take both forms?

The short answer to this is YES, you can take both for extra fat burning power.

But, as explained previously, they should be taken at different times. You don’t necessarily need to take both though. You could just go with the acetyl-l-carnitine, which will give you the best of both worlds.

Take this first thing before breakfast, along with your green tea, coffee, or any of these other metabolism boosting drinks to boost brain power and cognitive function for the day. This means you will reap the fat burning and anti aging benefits as well.

Just to be clear, acetyl-l-carnitine is sometimes marketed as N-Acetyl Carnitine (abreviation NAC), which are both exactly the same thing, just with different names.

Possible Side Effects

If the dosage is correct for you and kept within the recommendations, then there are very few side effects to l-carnitine supplementation. This makes it a mostly safe and popular supplement.

Be sure to take your time to buy from  trusted l-carnitine brands only. You need to be absolutely sure about what you are getting. Make sure to look for highly recommended products with good customer reviews.

Side effects, when they do occur, include nausea, vomiting, stomach cramps and diarrhea. But, this only usually happens when taken at too high a dosage.

More serious side effects can include elevated heart rate, high blood pressure and fever. In these cases the supplements should be stopped immediately and medical advice sought.

zestforever fit program


Thank you for reading this article from ZestForever!

Please remember that supplements are not intended to treat or cure medical diseases.

You should always consult your doctor before using them for this purpose.

These kind of supplements always work better alongside a structured healthy eating and fitness plan, such as our ZestForever Fit Program. These easy exercises and plant powered meal plans make getting that vibrant, healthy, fit body way easier to achieve than if you were to go it alone.

Comments are welcomed below. Please let us know your thoughts and experiences.

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23 thoughts on “What are L-Carnitine Benefits and Side Effects?”

  1. I didn’t know all the details about l-carnitine before reading this post. I have trouble with retaining fat and not being able to burn it off, and have been looking for ways to solve that through nutrition. and if I’m being honest, I could also use more brain power! think I’ll give this a shot, it sounds like it could really help.

    1. Hi Penelope, yes this could well be what you need but it only really works well if you are on a proper exercise regime as your body needs the stress of exercise on the muscles to start the repair and building process AND to strip fat. I have many more fat burning tips on my website zestforever.com you should take a look. Please feel free to let me know if you have any more questions. Thanks

  2. I did not know that L-Carnitine could benefit as an anti-aging supplement. I have long been a believer in L-Carnitine and am needing to purchase more. I see the link for the Acetyl L-Carnitine, but do you also have a link to purchase straight up L-Carnitine? I have always purchased the Acetyl, but am thinking I would like to see how this will help my ability to burn fat. Thanks!

    1. Hi Matts mum, I’m really interested to hear that you have used L-Carnitine before. How well has it worked for you? Also, do you do regular exercise with it? I will be putting a link on my website for straight up L-Carnitine within the next few hours. I am going to look for a good quality but low price one and I will get it on there. Please take a look later and I will put the link in at the bottom of my post next to the Acetyl L-Carnitine link. Thanks

  3. I never heard of L-Carnitine, so this was definitely a good.

    I’m just finishing a book on cleansing, something that want to do in the near future. I was wondering if L-carnitine would be something that would be OK to take while on the cleanse, or would it be recommended to wait until after the cleanse is completed?

    1. Hi Veronica, I would say, if you are doing a cleanse then wait until you have finished. Mainly because, normally on a cleanse (this depends on what sort of cleanse and how low calorie it is) you wouldn’t be doing lots of physical exercise as it is normally recommended not to, so as your body can concentrate on cleansing.

      And I would only recommend the L-Carnitine whilst in some kind of regular physical exercise or training program, where you will be tearing muscles and rebuilding them stronger. Also, L-Carnitine is only a fat burner when combined with exercise as it helps the body burn fat for fuel mostly whilst training. Hope this makes sense and please let me know if you have any more questions. Thanks

  4. So happy I read this, I’m going to look into getting some. This is the first I’v heard of it. I just started working out, my goal is to get rid of the rolls. Thank you for this article

    1. Hi Toni, I’m really glad this has helped you and since I have researched it so thoroughly I have decided to try it for myself to try and get rid of that stubborn fat that doesn’t seem to go away no matter what you do. I’d go for the Acetyl L-Carnitine like I said in my post and start on a low dose to see how it goes, then maybe build up.

      You should also read my post on Top 20 Fast Fat Burning Foods and try and incorporate as many as you can into your diet. Let me know if you have any more questions and I will be happy to help.

  5. Hi Stephanie,
    Great article on L-Carnitine, thanks for sharing. I can tell you are very knowledgeable in supplements and the like and come from a place of passion. The days in which I take additional supplements are behind me, or so I thought. With the anti-aging benefits as well as faster recovery and higher testosterone, I might have to check into it. Thanks for sharing!
    Mat A.

    1. Hi Matt, thanks for reading, and I’m glad you liked the article. I only recommend L-Carnitine if you are in regular training but it looks to me like you are judging from your profile pic ha ha. I have 2 personal trainers that I work closely with who say they see great results with this stuff. One of them also told me that the effects are even better when stacked with glutamine and creatine. So yes you should maybe look into it or try for yourself. If you do then please let me know how you get on as I would be very interested in your results. Thanks

  6. I have been doing intermittent fasting for over a year and I actually want to look leaner. I want to take l-carnitine but when should I take it for best results?

    1. Hi Furkan, yes fasting is a great way to boost detoxification and also keep weight under control, although I find it very hard to do as I like my food so much! As for L-Carnitine, if you are taking straight up L–Carnitine for fat loss and muscle building purposes then it is best to take after a meal that contains lots of carbohydrates and protein (ideally a post workout meal).

      If you are taking the Acetyl L-Carnitine, which is primarily to boost brain power and cardiovascular health but still also has the fat burning/muscle building effect, then you should take this on an empty stomach first ting in the morning.

      Personally I would go for the Acetyl L-Carnitine as you seem to get the best of all worlds with that. But you could always experiment to see what works best for you. A personal trainer friend of mine swears by stacking straight up L-Carnitine with glutamine and creatine for the best results. Hope this helps you and please let me know if you have any more questions.

    2. Hi,
      Very informative…I need to know can Acetyl L-Carnitine 1000 mg tablets is suitable Pre workout or post workout?? And can I also take my daily multivitamins with it?
      Thanks a lot!!!

      1. Hi there, thanks for the question. The best time to take Acetyl L-Carnitine is after your workout, but you can also take it with any carbohydrate containing meal. For example, on days that you are not working out.

        And yes, you can still take your multivitamin as most multivits don’t contain l-carnitine, or if they did it would only be in a tiny dose that wouldn’t make any difference at all. L-carnitie is a bulky supplement, unlike many vitamins and trace minerals, which can be packed into a tiny tablet. Hope that helps!

      2. Hey there, thanks for the question. I am sorry if you have received 2 replies to this but I realised after I uploaded my first comment that you where talking about ACETYL L-Carnitine and not the straight. Anyway, acetyl is best taken in the morning on an empty stomach as it will be better absorbed by the brain and muscles before food.

        Also, yes you can take an extra multivitamin as most multivits will not contain l-carnitine, or if they do it will be in very small amounts. Unlike trace minerals and most vitamins, l-carnitine is a bulky substance and would be hard to fit into a tiny tablet. Same goes for nutrients such as omega 3 oils, magnesium, certain B-vitamins, and vitamin C, which is why you usually need a separate supplement for these things if you want to get them in higher doses.

        Hope that helps, and feel free to contact me if you have any further questions!

  7. I had heard that L-CARNITINE could help with weight loss, but I never really knew of the other benefits such as anti aging and increased energy.
    Another thing I did not know was that you could get it from veggies!
    I have recently gone the way of the vegetarian and this is good to know!
    Any brands you would recommend as the best as far as supplements go?

    1. Hi Brendon, yes L-Carnitine is in veggies but not in as high amounts as say red meat (which has the highest), so it is crucial you make sure you get an all round healthy diet when you go vegetarian/vegan to stop any deficiencies.

      As for recommended brands, I would always go for something well trusted and organically derived. A few trusted brands that I know of are Viridian, Solgar, Nature’s own, Nature’s plus but I hope these are available to you, depending on where you live.

  8. Hello and thanks for sharing, this seems to be pretty amazing and seems to benefit the body in so many ways it is got to know that there are products such as this on the market that can really get the job done of burning fat and all of that other good stuff that comes along with this product. I am sure that your readers will find what you are sharing to be of great value.

    1. Hi Norman, I am glad you enjoyed the article on L-Carnitine. It’s one of those things that most people have never heard of but it’s such a great supplement, especially for those in training who would like to burn fat and build muscle. In fact I have a great little post on doing just that if you are interested How to Burn Fat and Build Muscle

    1. Hi Gary, according to Healthline, dosage is between 600-2,500mg per day for n-acetyl. You should start low and work up always with any supplements to see how well they work and if indeed you have any side-effects. Obviously, you should try and find the dose that is right for you and not take too much as it would be a waste of money if nothing else.

      You are not too big a guy weight wise, and without knowing your body’s composition I would say you shouldn’t need to go up to the highest end of the dose scale.

      You should also take into consideration the labeling on the brand you are using, and feel free to email companies to ask for more info about your specific case as they usually have a trained nutritionist on their team.

  9. Pingback: What are L-Glutamine Benefits and Side Effects?

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