The Complete Guide to Fat Oxidation

A female athlete's torso with a measuring tape on her midsection

Burning fat is big business. One need only look at the gross revenue of the weight loss industry, which just so happens to be a $66 billion dollar a year industry <1,2>, for proof that there’s of money to be made helping people lose unwanted body fat.

Over the decades, all sorts of pills, potions, and powders have been released with the single goal of helping the individual who struggles to maintain an ideal body composition. And, for a time, people do experience some success with their individual weight loss ventures - in the short, that is.

You see, as much money as the fat loss industry generates each year, it hasn’t translated to long-lasting results for the consumer. Roughly 70% of the United States population is overweight or obese, with the percentage of 12-17-year-olds who are overweight doubling since 1980.

Additionally, about 95% of people who are overweight or obese that do try a diet end up regaining the lost weight (and sometimes more) back within one year of their attempt at dieting.

Suffice it to say, that the current weight loss system isn’t very effective, regardless of how profitable it is.

And before you blame the industry, you need to realize that both sides are at fault. The consumer can’t stick to his or her diet, and the industry pushes diets that aren’t sustainable and supplements that are quasi-effective at best.

So, since the current system isn’t working particularly well, what can we do to improve fat loss for the consumer and help them drop the fat once and for all?

Educate them.

Like most things in life, the better you understand a subject, the more likely you are to be able to apply its principles and experience success.

So, with that in mind, let’s discuss the ins and outs of how your body burns fat.

Fat Burning vs. Fat Oxidation

First off, let’s get some terminology taken care of.

When discussing fat burning, what we’re actually talking about from a physiological standpoint is the oxidation of fat.

What does fat oxidation mean?

As you probably know, fat cells (adipose tissue) are the primary storage site of body fat, and they are in a constant state of turnover, meaning that fat is continuously entering or exiting the cell-based of several factors including hormones, nutrition, and metabolism.<3> The net effect of these factors determines the number of fatty acids that are circulating in your bloodstream as well as how much body fat is stored.

Fat is stored in adipose tissue as triglycerides. These triglycerides are released into the bloodstream via the actions of the enzyme Hormone-Sensitive Lipase (HSL) <3,4> where they can then be burned (“oxidized”) for energy.

This process of stored fatty acids being released into the bloodstream to be used for energy production is known as lipolysis.

What Happens during Fat Oxidation?

Fat oxidation can essentially be broken down into three phases:

  • Lipolysis
  • Mobilization
  • Oxidation

Lipolysis: Releasing Stored Fat

Triglycerides are composed of a glycerol “backbone” and three fatty acids. In order for your body to burn the fatty acids, they must first be separated from the glycerol molecule. For this to happen, an enzyme called lipase cleaves the fatty acids from the glycerol via hydrolysis. <3,4>

Mobilization: Transporting Fat for Oxidation

The second phase of fat burning comes in the form of fatty acid mobilization.

After separation and release from the fat cell, the fatty acids then enter the bloodstream where they circulate bound to a protein called serum albumin.

Serum albumin acts as a “taxi” of sorts that helps shuttle the fatty acids to the target cell requiring energy. and enter muscles to be “burned.”

The reason fatty acids require the shuttling actions of albumin is due to the fact that blood is composed mostly of water. As you’ve seen first-hand if you’ve ever whipped up your own salad dressing, water and oil don’t mix together all that well. This is due to the fact that fat is not water-soluble, meaning it doesn’t dissolve in water. <5>

As such, albumin serves as the protein carrier that taxis fatty acids through the bloodstream to the muscle cell when they are needed. Each albumin protein can carry with it several fatty acids. <5>

Upon arrival at the target cell, we enter the final phase of the fat burning process...

Oxidation: Burning Fat for Fuel

As the fatty acids enter the cell, they are stored in the cytoplasm of the cell, which is the thick solution that fills the inner regions of the cell. But, we don’t want the fatty acids to remain in the cytoplasm.

In order for them to be converted into ATP (i.e. burned for energy), they must enter the mitochondria of the cell, which can be thought of as each individual cell’s mini-nuclear reactor that generates the energy required to power the cell.

Now, the actual process of converting the fatty acids to ATP is called beta-oxidation. It’s a multistep process that in and of itself requires a lengthy discussion and deep dive into biochemistry that would put most of you to sleep.

For the purposes of this article, just know that the beta-oxidation is the process by which your body obtains energy from fatty acids.

Fatty acids are shuttled from the cytoplasm into the mitochondria via the actions of a substance called carnitine, which many of you have probably seen in your favorite fat burning supplements, such as Steel Sweat.

Once converted into ATP, the energy can then be used by the cell to power it to perform whatever sort of activity you might be performing (weight lifting, cardio, walking, laying on the sofa, etc.)

But, what happens if there’s no immediate need?

In certain cases (i.e. starvation, fasting, etc.) high amounts of fatty acids are broken down and subsequently flood the mitochondria. Since there’s not a high demand for energy from the muscles, the fatty acids are converted into ketones, where they can then be used by the brain and muscles as a source of energy.

These ketone bodies are rich in energy and the preferred source of energy for people following low-carb, ketogenic, and zero carb diets.

How to Increase Fat Oxidation

Since most people entering the fitness space are wanting to lose fat, it would make sense to discuss what things we can do to enhance fat oxidation and accelerate fat loss.

Reduce Calories

One of these ways is by reducing caloric expenditure, i.e. creating a calorie deficit. When you reduce the number of calories you’re consuming, your body has to make up for the lack of energy (food) you’re ingesting to suffice its energy requirements from pulling from your fat stores.

This is why in order to lose fat, cutting calories is one of the main things you have to do. Weight loss ultimately boils down to energy balance in the body, i.e. calories in vs calories out. To create a negative energy balance, you can decrease the number of calories your intake, and increase the number of calories you “outtake”, which is accomplished through exercise.

Regulate Insulin Levels

Earlier in this article, we discussed the importance of hormone-sensitive lipase in the liberating of stored fatty acids from adipose tissue. There exists another hormone, which you’re probably very familiar with, that opposes the actions of hormone-sensitive lipase called insulin.

Insulin is the hormone in your body that is responsible for driving nutrients into your cells, including muscle and fat cells, which can then be used for energy production.

The main macronutrient that causes insulin levels to rise is carbohydrates and seeing that insulin effectively shuts off the fat burning process, maintaining low levels of insulin is essential to maximizing fat burning.

This is why so many ketogenic, low carb, no carb diets restrict carbohydrate intake. They’re trying to limit the amount of insulin that is released, so that you’re burning more and more fat, rather than glucose.

But, just because we’re trying to burn fat doesn’t mean that we have to avoid any and all carbohydrates.

You can still have your carbs and burn body fat, but it requires some proper nutritional selections on your part.

Simple sugars create larger insulin spikes in the body than complex carbohydrates or protein. If you’re trying to maximize fat burning, you want to opt for things like green vegetables, berries, avocados, as well as proteins, which create lower insulin spikes and promote fat burning.

But, let’s say that a few times per week you still want to have a sweet treat, and still lose fat.

Is there anything you can do?


And it comes in the form of...


As we stated above, increasing your calories out is one of the ways you can tip energy balance in favor of fat loss. This, of course, is accomplished through exercise, and we can maximize fat burning by performing the right types of exercise.

Science has pretty clearly shown that during exercise, your muscles can use both dietary carbohydrate and fat operate as substrates used for energy. <7,8,9> However, there are a few factors that affect which macronutrient your body uses for energy. Factors affect substrate utilization include <10>:

  • Diet

    If you’re consuming a low carbohydrate diet and/or going into your workout fasted, you will burn fat for fuel.

  • Muscle glycogen content

    Your body has a finite amount of glycogen stored in the muscle. Once these stores are exhausted, the body will start pulling from your fat stores for energy.

  • Exercise intensity

    Low to moderate intensity forms of exercise primarily use fat as their source of energy. The higher you go with exercise intensity, the more you shift to burning glycogen and glucose.

    Research notes that maximal rates of fat oxidation are achieved when training at intensities of 59-64% of maximum oxygen consumption in trained individuals and between 47-52% of maximum oxygen consumption in the general population. <6>

  • Duration of training

    The longer you train, the more you deplete glycogen and once those stores are depleted, you will switch to burning fat for fuel.

  • Training status

    The more “fit” you are, the harder you can exercise before shifting from fat burning to glucose burning. Additionally, the more fit you are, the lower your resting insulin levels will be, thus allowing you to burn more fat outside of your eating windows.

Due to these factors, you can begin to understand why most fasted cardio sessions are performed at a relatively low intensity -- it maximizes fat burning in the body.

Does that mean you should only perform steady-state cardio when trying to lose body fat?

No, not at all.

There’s something known as EPOC (excess post-exercise oxygen consumption), which is science speak for the “afterburn” effect created by a high-intensity exercise where your body continues to burn calories even after your training session is over.

Steady-state cardio, while it burns more fat during the actual time you’re exercising compared to interval-based cardio, has virtually no effect on EPOC, which means that once you stop performing your steady-state cardio, the calorie burns stop.

This is why you’re still able to lose fat even without performing any steady-state cardio whatsoever. The oxygen deficit created by high-intensity forms of training such as weight lifting or interval training leads to greater overall calorie burning as your body works to restore homeostasis.

Your body uses oxygen to:

  • Regenerate ATP that was burned during the workout
  • Resynthesize of muscle glycogen depleted during training
  • Restore oxygen levels in the blood
  • Repair muscle tissue damaged during the workout
  • Restore core temperature to resting (homeostasis) levels

Each of these actions requires a certain amount of energy to be carried out, and if you’re in a caloric deficit, that energy comes from your fat stores.

This is why high-intensity interval training can aid fat loss even though you’re technically not using fat as a fuel during the actual workout.

The point of this is to say that both steady-state and high-intensity interval training can be used to lose body fat. The mechanisms by which they work are different, but the end result is the same. <11>


Fat burning is a billion-dollar industry, yet very few people actually understand the theory and science of what it takes to burn fat, and even fewer know how to apply it to daily life.

Hopefully, this guide has shed some light on manageable ways to burn more fat in your daily routine, so that you can achieve the body you’ve always wanted.

And, if you need some help burning extra calories and shifting your body towards a greater fat burning environment, check out Steel Sweat.

Steel Sweat is the ideal pre-workout for fasted training. Not only does it include ingredients such as caffeine which help release fatty acids to be burned for energy it also includes several pro-fat burning compounds, such as L-Carnitine L-Tartrate and Paradoxine, which take those liberated fatty acids and burn them for energy.

Steel Sweat can help you burn fat like never before and achieve the results you’ve always wanted and more!

Post your weight loss improvements on Instagram and tag @steelfitusa with the hashtag #IAMSTEELFIT for a chance to be featured!


  3. Arner, P. (2005). Human fat cell lipolysis: biochemistry, regulation and clinical role. Best Practice & Research. Clinical Endocrinology & Metabolism, 19(4), 471–482.
  4. Lass A, Zimmermann R, Oberer M, Zechner R. Lipolysis – A highly regulated multi-enzyme complex mediates the catabolism of cellular fat stores. Progress in Lipid Research. 2011;50(1-4):14-27. doi:10.1016/j.plipres.2010.10.004.
  5. Holloway, G.P., Luiken, J.J.F.P., Glatz, J.F.C., Spriet, L.L., & Bonen, A. (2008). Contribution of FAT/CD36 to the regulation of skeletal muscle Fatty acid oxidation: an overview. Acta Physiologica, 192, 293-309.
  6. Achten, J., & Jeukendrup, A. E. (2004). Optimizing fat oxidation through exercise and diet. Nutrition (Burbank, Los Angeles County, Calif.), 20(7–8), 716–727.
  7. FRAWLEY K, GREENWALD G, ROGERS RR, PETRELLA JK, MARSHALL MR. Effects of Prior Fasting on Fat Oxidation during Resistance Exercise. International Journal of Exercise Science. 2018;11(2):827-833.
  8. Achten J, Gleeson M, Jeukendrup AE. Determination of the exercise intensity that elicits maximal fat oxidation. Med Sci Sports Exerc. 2002;34(1):92–97.
  9. Achten J, Jeukendrup A. Maximal fat oxidation during exercise in trained men. Int J Sports Med. 2003;24(08):603–608.
  10. Venables, M. C., Achten, J., & Jeukendrup, A. E. (2005). Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. Journal of Applied Physiology, 98(1), 160–167.
  11. Zhang H, Tong TK, Qiu W, et al. Comparable Effects of High-Intensity Interval Training and Prolonged Continuous Exercise Training on Abdominal Visceral Fat Reduction in Obese Young Women. Journal of Diabetes Research. 2017;2017:5071740. doi:10.1155/2017/5071740.
  12. Foureaux, G., Pinto, K. M. de C., & Dmaso, A. (2006). Effects of excess post-exercise oxygen consumption and resting metabolic rate in energetic cost. Revista Brasileira de Medicina Do Esporte, 12(6), 393–398.

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