Andy-Just-Gyms
Active member
- Nov 25, 2025
- 68
- 114
Intro
L-Carnitine is one of the most widely known compounds in the fitness industry that is utilized for fat loss. While there are many other documented benefits of L-Carnitine, this article will address L-Carnitine from its use in fat loss only. L-Carnitine is an amino blend naturally occurring in the body. Exogenous administration of L-carnitine is not banned by the World Anti-Doping Agency (WADA) so this compound is frequently used by natural competitors to assist in fat loss. But how does it work? Let's talk about it.
The Carnitine Shuttle
To understand how L-carnitine works and what it does, one must understand the complex physiology of the carnitine shuttle. I will attempt to break it down into easily digestible pieces for the reader.
Fatty Acids are the functional unit of adipose tissue, or body fat. The body has to break down body fat in very tiny pieces in order for it to be "burned" or oxidized in the mitochondria, the powerhouse of the cell. However, not all fatty acid chains are small enough to actually get into the cell and be utilized by the mitochondria. This is where carnitine comes into play.
L-Carnitine binds to the longer fatty acid chains and cause them to "fold" or "bend" so that they can actually fit through the cell membrane and get to the mitochondria for use. There are a lot of steps that occur and I don't want to confuse the reader, so I'll explain the process in a nutshell.
What is "Normal"?
As mentioned, carnitine is a molecule made up of amino acids, the building blocks of protein. Most people get enough carnitine through their diet and as such, carnitine works in the body without exogenous administration. So why would someone consider adding additional L-Carnitine?
Okay, I get it. Exogenous L-Carnitine can potentially help me utilize body fat for energy. So how do I do this?
Great question, I'm glad you asked. As listed above, low carb diets do well with adding carnitine because with the body's preferred energy source limited, the body will utilize fat for ATP production in the mitochondria.
Hold on, before you ask... You don't have to completely cut out carbs. You will have some depletion of carbs, and you can use your intramuscular glycogen for your exercise. Eventually, your glycogen stores will deplete and you're only having enough carbs for your performance, but if you're trying to lose body fat, you're going to be in a calorie deficit. So the body on lower carbs gets primed to use body fat for energy.
Okay, thanks. So I can drink that Carnitine product they have on TikTok ads and Instagram ads right?
Uhh... sort of. See oral carnitine has to go through the entire digestive system and then get absorbed into the body through the intestines, into the liver, and then to the rest of the body. So what happens is the amount of oral carnitine that you consume, ends up being only about 10-20% leftover for use. So you can technically use oral carnitine, whether it is a a liquid or a powder that you add and consume. But to get to a reasonable dose, you're going to have to consume around 2000-4000mg. This can be a bit harsh on your digestive system, and while it works, its not the best option.
Injectable L-Carnitine can be administered intramuscularly where the blood vessels are flowing through because you're definitely trying to get a pump, you stud. The carnitine is then readily available and absorbed into the blood stream and completely bypasses the acidic environment of your stomach acid, all of your food and digestive tract, and clearance by the liver. In fact, injectable L-Carnitine is about 95-98% bioavailable depending on the literature you read.
One key with L-Carnitine: it requires insulin to work. Your body produces insulin in response to carbohydrates to shuttle glucose into the cell.
Wait. You said low carb diets, but I hear people utilize L-carnitine for fasted cardio. Doesn't that mean it won't be fasted cardio since I need carbs to get insulin for the carnitine to work?
Yes... and No... let me explain.
Your body will continually produce insulin for glucose in your system. Eventually, that can cause your glucose to be completely depleted, which is bad because your brain feeds on glucose, and a situation like that will cause you to pass out and go into a coma. So your body, specifically your liver, has the process called gluconeogenesis. And like the word sounds, it creates new glucose. This occurs when you are sleeping. So when you wake up, your body has created "some glucose" and initiated a response by the pancreas to secrete "some" insulin. This is why L-carnitine works with fasted cardio.
A special consideration. Insulin does not speed up the fat oxidation, and lack of insulin does not slow fat oxidation. Insulin is used only in the transport of the linked Carnitine and fatty acid chains into the cell. Once there, your body will process it normally. So low insulin will just make the transport take longer, not the fat oxidation take longer.
Conclusion
L-Carnitine is a useful tool in the path and process of fat loss and understanding how best to apply these concepts to your lifestyle can provide a lot of benefit. Just keep in mind, there is no substitute for a structured diet, training program, sleep schedule, and the mindset to stay dedicated and consistent to the goals you have set for yourself. L-Carnitine is just a tool to assist someone already consistently compliant with the fundamentals of a healthy lifestyle.
Hope you enjoyed the read.
-Andy
L-Carnitine is one of the most widely known compounds in the fitness industry that is utilized for fat loss. While there are many other documented benefits of L-Carnitine, this article will address L-Carnitine from its use in fat loss only. L-Carnitine is an amino blend naturally occurring in the body. Exogenous administration of L-carnitine is not banned by the World Anti-Doping Agency (WADA) so this compound is frequently used by natural competitors to assist in fat loss. But how does it work? Let's talk about it.
The Carnitine Shuttle
To understand how L-carnitine works and what it does, one must understand the complex physiology of the carnitine shuttle. I will attempt to break it down into easily digestible pieces for the reader.
Fatty Acids are the functional unit of adipose tissue, or body fat. The body has to break down body fat in very tiny pieces in order for it to be "burned" or oxidized in the mitochondria, the powerhouse of the cell. However, not all fatty acid chains are small enough to actually get into the cell and be utilized by the mitochondria. This is where carnitine comes into play.
L-Carnitine binds to the longer fatty acid chains and cause them to "fold" or "bend" so that they can actually fit through the cell membrane and get to the mitochondria for use. There are a lot of steps that occur and I don't want to confuse the reader, so I'll explain the process in a nutshell.
- Long Fatty Acid chains are free floating within the blood plasma.
- An enzyme links the fatty acid chain to L-carnitine.
- The molecular compound then "seeps" into the cell through the cell membrane.
- Another enzyme breaks the fatty acid chain away from the L-carnitine molecule.
- The fatty acid chain enters the mitochondria and is utilized for energy via the electron transport system.
What is "Normal"?
As mentioned, carnitine is a molecule made up of amino acids, the building blocks of protein. Most people get enough carnitine through their diet and as such, carnitine works in the body without exogenous administration. So why would someone consider adding additional L-Carnitine?
- Genetic Carnitine Deficiency - inability to produce carnitine
- Vegetarian/Vegan - lack of carnitine from the diet
- High Cortisol/Stress - blunts carnitine production
- Low Carb Diets - primed for utilizing fatty acids for energy.
- Insulin resistance/PCOS - insulin is required for the carnitine shuttle (more on this later)
Okay, I get it. Exogenous L-Carnitine can potentially help me utilize body fat for energy. So how do I do this?
Great question, I'm glad you asked. As listed above, low carb diets do well with adding carnitine because with the body's preferred energy source limited, the body will utilize fat for ATP production in the mitochondria.
Hold on, before you ask... You don't have to completely cut out carbs. You will have some depletion of carbs, and you can use your intramuscular glycogen for your exercise. Eventually, your glycogen stores will deplete and you're only having enough carbs for your performance, but if you're trying to lose body fat, you're going to be in a calorie deficit. So the body on lower carbs gets primed to use body fat for energy.
Okay, thanks. So I can drink that Carnitine product they have on TikTok ads and Instagram ads right?
Uhh... sort of. See oral carnitine has to go through the entire digestive system and then get absorbed into the body through the intestines, into the liver, and then to the rest of the body. So what happens is the amount of oral carnitine that you consume, ends up being only about 10-20% leftover for use. So you can technically use oral carnitine, whether it is a a liquid or a powder that you add and consume. But to get to a reasonable dose, you're going to have to consume around 2000-4000mg. This can be a bit harsh on your digestive system, and while it works, its not the best option.
Injectable L-Carnitine can be administered intramuscularly where the blood vessels are flowing through because you're definitely trying to get a pump, you stud. The carnitine is then readily available and absorbed into the blood stream and completely bypasses the acidic environment of your stomach acid, all of your food and digestive tract, and clearance by the liver. In fact, injectable L-Carnitine is about 95-98% bioavailable depending on the literature you read.
One key with L-Carnitine: it requires insulin to work. Your body produces insulin in response to carbohydrates to shuttle glucose into the cell.
Wait. You said low carb diets, but I hear people utilize L-carnitine for fasted cardio. Doesn't that mean it won't be fasted cardio since I need carbs to get insulin for the carnitine to work?
Yes... and No... let me explain.
Your body will continually produce insulin for glucose in your system. Eventually, that can cause your glucose to be completely depleted, which is bad because your brain feeds on glucose, and a situation like that will cause you to pass out and go into a coma. So your body, specifically your liver, has the process called gluconeogenesis. And like the word sounds, it creates new glucose. This occurs when you are sleeping. So when you wake up, your body has created "some glucose" and initiated a response by the pancreas to secrete "some" insulin. This is why L-carnitine works with fasted cardio.
A special consideration. Insulin does not speed up the fat oxidation, and lack of insulin does not slow fat oxidation. Insulin is used only in the transport of the linked Carnitine and fatty acid chains into the cell. Once there, your body will process it normally. So low insulin will just make the transport take longer, not the fat oxidation take longer.
Conclusion
L-Carnitine is a useful tool in the path and process of fat loss and understanding how best to apply these concepts to your lifestyle can provide a lot of benefit. Just keep in mind, there is no substitute for a structured diet, training program, sleep schedule, and the mindset to stay dedicated and consistent to the goals you have set for yourself. L-Carnitine is just a tool to assist someone already consistently compliant with the fundamentals of a healthy lifestyle.
Hope you enjoyed the read.
-Andy
