L-Carnitine Benefits and Side Effects

You have probably only heard about l-carnitine if you are in the health and fitness industry, where it is most widely used and talked about for its performance enhancing and fat burning qualities.

But let’s take a look at the science behind the hype and see if this really is a supplement worth its salt. In this post we will take a look at l-carnintine benefits and side effects to see if it’s suitable for your specific needs.


So What Exactly is L-Carnitine?

human brain

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

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



L-carnitine is mostly found in animal products and especially red meat (56-162mg per serving), but is also found at much lower levels in sorces such as poultry, fish and seafood (3-7mg) and dairy products (3-8mg).


What About Vegan Diets?

black beans in a heart shape

 L-Carnitine can be found in plant sources such as tempeh, avocados and peanuts, but not at very high levels. The good news is l-carnitine deficiency is rare, even in strict vegans.

We can produce our own l-carnitine in our liver and kidneys from the other amino acids methionine and lysine, all of which are abundant in other plant foods such as nuts, seeds, lentils, wholegrains, tempeh, quinoa, seitan, black beans and soya milk.

This is the reason l-carnitine deficiency is rare because we have plenty of opportunity to make our own from the methionine and lysine we consume in our everyday food. Deficiency is usually only found in those who have kidney and liver function problems as they cannot produce their own adequate supply.


The Science Behind L-Carnitine

spinning class

Commonly used in the fitness industry for its ability to stimulate the release of growth hormone and help reduce body fat, l-carnitine 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. It is however, most effective when you are engaging in very intense exercise.

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




toned stomach

A study from the University of Nottingham confirmed that when the athletes in their trial consumed 2g of l-cartinine along with 80g of high G.I. carbohydrate, both as soon as they wake up and before food, then again 4 hours later for 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, means you will have more stamina to train for longer – hence you will burn more fat and build more muscle.



man eating a burger

The athletes on the trial, although eating an extra 640 calories of high G.I. carbs,  gained no extra body fat whilst supplementing the l-carnitine; while the group eating the extra carbohydrates without the supplement put on more than 5lbs in weight of fat.

This is not to advocate a high G.I. diet, and this was just used as an example in the trial to prove how effective l-carnitine is at burning fat. Unless you really are working out like a true athlete then I would recommend sticking with a lower G.I. diet.



The subjects on the same trial that were supplementing the l-carnitine were also able to go a whopping 25% longer due to the fact that fat was being burned for fuel first rather than muscle glycogen, therefore staving off fatigue. This is the the reason l-carnitine allows you to train for longer periods before tiring.



L-carnitine has been shown to significantly 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 which can lead to you missing sessions, or not putting your all in when you need to due to pain.

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



Yes you heard me right! L-carnitine boosts brain cells and helps to keep the brain young. Its powerful antioxidant effects slow down the aging process and help to keep the brain and heart young.

And this slowing down of the aging process does not just mean on the outside, but on the inside too as it will also lower your risk of age related degenerative diseases such as alzheimer’s and heart disease.



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

Don’t worry you can still take this supplement if you are a woman without worrying about turning into Arnold Schwarzenegger, as the effects will be subtle and toned.



shots of green superfood powder

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 l-carnitine is with a meal that contains both carbohydrates and protein. This applies to some of the other forms available 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 without food. This type of l-carnitine can be taken along with other healthy fat burners such as green tea or a green superfood shot, to boost effects.

You should also incorporate lots of fat burning plant foods into your diet along with any supplements you may be taking, such as l-carnitine, if you want the best results and for the FASTEST way to get a great body. 



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

It is also good for the support of the cardiovascular and nervous system, and for memory and brain power. This form of carnitine also helps burn fat for fuel just like regular l-carnitine, but is actually primarily used for the other effects.



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

It is worth noting that there are other primarily brain boosting forms of carnitine, such as Propionyl-l-carnitine and l-carnitine l-tartrate and these should also be taken alongside food.



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 (which is a fat burner) to boost brain power and cognitive function for the day – plus reap the fat burning benefits as well.

On a side note, acetyl-l-carnitine is sometimes marketed as N-Acetyl Carnitine (abreviation NAC), and these are both exactly the same thing but 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, making this a mostly safe and popular supplement.

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 which case the supplements should be stopped immediately and medical advice sought.


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Stefanie Taylor

I have studied nutrition for many years, and have since discovered that a plant based diet has been the most beneficial to my health and body. I have more energy and zest for life than I have ever had and this website is dedicated to helping others who wish to know more, and start out on this lifestyle.


Penelope · 31/10/2017 at 12:55 pm

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.

    Stefanie Taylor · 31/10/2017 at 5:21 pm

    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

Matts Mom · 31/10/2017 at 2:27 pm

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!

    Stefanie Taylor · 31/10/2017 at 5:26 pm

    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

Racky Khangjrakpam · 31/10/2017 at 2:49 pm

Its awesome review about L Carnitine I ever come across. I like to try it and thank you for this review.

    Stefanie Taylor · 31/10/2017 at 5:14 pm

    Thank you Racky, I am glad you enjoyed it. Please feel free to check out similar posts at and let me know what you think.

Veronica Wanzer · 31/10/2017 at 2:49 pm

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?

    Stefanie Taylor · 31/10/2017 at 10:10 pm

    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

Toni · 31/10/2017 at 4:15 pm

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

    Stefanie Taylor · 31/10/2017 at 5:10 pm

    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 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.

Mat A. · 31/10/2017 at 5:48 pm

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.

    Stefanie Taylor · 31/10/2017 at 10:15 pm

    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

Furkan · 31/10/2017 at 11:22 pm

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?

    Stefanie Taylor · 01/11/2017 at 9:37 am

    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.

Brendon · 08/11/2017 at 6:42 pm

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?

    Stefanie Taylor · 08/11/2017 at 6:42 pm

    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.

Norman · 06/01/2018 at 5:14 pm

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.

    Stefanie Taylor · 07/01/2018 at 10:04 am

    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

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