Eleven Myths and Facts About How the Body Burns Fat

A common myth in the casual fitness world is that there is a “fat-burning” zone that will allow you to burn the most body fat.

The reality is that working out in the fat burning zone doesn’t measure up as the ideal exercise mode for losing body fat. Most important for fat loss is that the energy (calories) that is entering the body is less than the energy leaving the body.

There are lots of ways of making this happen. This article will give you 11 fat loss facts, covering everything from how the body burns energy to when and how to focus on enhanced fat burning so as to optimize body composition.

#1. Knowing where and how energy is stored in the body will improve fat loss results.

Your body has the following energy sources available to it, which it burns at different rates depending on the intensity of physical activity:

Body fat provides roughly 30,000-100,000 calories in normal-weight people, depending on how much body fat you actually have. In obese people, the number is much higher.
Muscle glycogen provides 1,400-2,000 calories or 350-500 grams of glycogen, which is enough for 90 minutes of endurance exercise. It is stored in muscle cells and used by those cells for energy.
Liver glycogen provides about 400 calories or 100 grams of glycogen. It can be turned into glucose and used by the rest of the body, such as the brain and blood cells.
There’s also muscle and tissue, which is made of amino acids and can be broken down to produce glucose. This is the not ideal because it leads to loss of lean mass.

#2. During exercise, the intensity of the exercise dictates the proportion of fat or carbohydrates being burned.

Fat is your body’s primary fuel when you haven’t just eaten and aren’t exercising (a state we call “at rest”). At rest, when you’re sitting at your desk or even going for a walk, your body is burning mostly fat, but depending on the need for energy (such as if you had to walk up three flights of stairs), you’re body may increase carb burning.

When you start exercising or lifting weights, you need a more rapid supply of energy. The percentage of fat used as fuel decreases in favor of carbs.

However, this increase in carb burning doesn’t mean that it will lead to less fat loss. In fact, as you increase exercise intensity and rely more on carbs, the amount of calories you burn increases exponentially as you require large amounts of energy to fuel your efforts.

Here’s an example: If you burn 200 calories per hour walking slowly, 60 percent is fat (120 calories) and 40 percent is carbs (80 calories). But if you burn 600 calories running at a pace of 8 minutes a mile, 40 percent is fat (240 calories) and 60 percent is carbs (360 calories).

The higher intensity exercise leads to more calories being used, more fat being burned, and more carbs being burned—all favorable effects for fat loss.

#3. After a strength training workout, there is a profound increase in the rate of fat burning in the post-workout period.

Research into energy use during strength training shows the following relevant facts:

The time spent lifting in traditional protocols results in minimal calories being burned, but after each set, energy use rises significantly. The most calories are burned between sets.
After a strength training workout, energy use is elevated for up to 24 hours over baseline, and the percentage of fat that is burned increases.
The increase in energy expenditure after strength training is generally equal to or greater than the increase following steady-state aerobic exercise. The increase in the use of fat for fuel is also greater with intermittent exercise than steady state.

#4. High-intensity training is most effective for fat loss because it elevates fat burning during recovery the most.

Both sprint training and circuit strength training with short or no rest between sets have a profound effect on post-workout calorie burn and the use of fat for energy.

For instance, a recent study found that after a high-intensity (HIT) strength workout that that took 32 minutes, trainees experienced a 24 percent increase in calorie burn equaling 452 calories in the 22 hours after the workout.

A traditional strength program that took double the time resulted in a 5 percent increase in calorie burn totaling 98 extra calories. This is average for strength workouts with long rest periods that allow for complete recovery between sets so as to maximize load.

In addition, the HIT group had a greater increase in the use of fat for energy over the post-workout period compared to the traditional group.

Another benefit of HIT-style programs is that they improve the body’s ability to burn fat at rest, which is known as metabolic flexibility. Metabolic flexibility is impaired in sedentary people, which is one reason that fat loss is so difficult when only modifying diet.

#5. Intermittent high-intensity exercise modes are favorable for fat loss because they build muscle mass.

The true power of exercise for producing fat loss is in the ability of anaerobic training to build lean muscle mass because it increases your total net calorie burn.

For example, a study that compared high-intensity training and endurance training found that the HIT group lost 9 times more body fat than the endurance group, while dramatically increasing metabolic flexibility.

Basically, researchers found that not only did the trainees burn more fat overall during and exercise and in the post-exercise recovery period, they also enhanced enzymes in the body that allow it to mobilize and use fat for energy all the time.

#6. Burning a large amount of carbs is beneficial for fat loss because it depletes muscle and liver glycogen stores.

If your glycogen stores are low, when you eat carbs, they get turned into glucose, which gets stored as glycogen. If your stores are full, the glucose goes to fat.

This is the reason that if you’re in a fat loss phase, you should do glycogen-depleting exercise and eat your carbs post-workout so that those delicious carbs go to glycogen rather than fat.

#7. Eating a low-glycemic meal pre-workout elevates energy expenditure and the use of fat for fuel in the post-workout period much more than training on an empty stomach.

Despite the consistent rumors that fasted cardio increases fat burning, research shows that when trainees eat pre-workout, they consistently burn more calories during the post-exercise recovery period in both moderate- and high-intensity ranges.

Additionally, there’s at least one study showing that the amount of fat burned during the 24-hour recovery period is significantly greater when trainees ate a meal before the workout.

#8. Supplementing with carbs before or during exercise will suppress fat burning and elevate carb burning. Fructose increases carb burning more than glucose.

Consuming carbs pre-workout leads to an immediate shift to the use of carbs for fuel. Drinking fructose is especially problematic because it not only increases the use of carbohydrates more than consuming glucose, it makes the cells more resistant to insulin.

Endurance athletes often use carbs in the latter stages of workouts to provide a fuel source when muscle glycogen has been used up. There are arguments for and against this practice that are out of the scope of this article. Know that for fat loss, carbs should be avoided pre- and during exercise.

#9. Supplementing with carnitine can increase fat burning and improve the overall use of energy at high intensities for optimal body composition changes.

Carnitine is a nutrient in the body that is critical for fat burning. It is responsible for the transport of fats into the cells to be used for energy.

Elevating carnitine stores has been found to reduce fat gain when eating a high-calorie diet because it increases energy expenditure. During exercise, greater carnitine stores lead to the sparing of glycogen for greater work capacity due to elevated fat burning.

The effect is a significant increase in time to exhaustion when training hard. Greater exercise capacity allows for more total calories to be burned, which is obviously favorable for losing body fat.

#10. Caffeine and fish oil enhance fat burning, however, they are not the magic bullet for fat loss.

Caffeine is the most well-known fat burner available. It encourages the fat in your cells to leave so that it can be burned for fuel. Research suggests doses between 3 and 8 mg/kg of body weight of caffeine as ideal for enhancing athletic performance.

Fish oil increases the activity of the uncoupling protein genes 1 and 3, which enhance fat burning and energy expenditure. Simply, the uncoupling proteins raise body temperature, increasing the amount of calories you burn.

#11. Dietary manipulation and genetics are key players in the body’s use of fat for fuel.

Genetics, diet, and gender also play a role. Women naturally burn more carbs at rest than men, but they burn more fat during exercise, making it imperative for all women to train if they want to get lean.

In one review of fat burning, scientists wrote that “66 percent of the variance (in the use of fat versus carbs for energy) could not be accounted for,” of which some was probably diet, but which the rest was likely genetically determined.

To manipulate fat burning with diet, adopt a high-fat, low-carb (70 percent fat, 20 percent carbs) diet for three days. Increasing carbs in favor of fat will have the opposite effect, enhancing the use of carbs during exercise. References

Sports Nutrition: Fuel Movement and Sport. University of Montana. Retrieved 15 January 2014. http://btc.montana.edu/olympics/nutrition/fuel03.html

Scott, C., Fountain, C. Estimating the Energy Costs of Intermittent Exercise. Journal of Human Kinetics. 2013. 38, 107-113.

Paoli, A., et al. High-Intensity Interval Resistance Training Influences Resting Energy Expenditure and Respiratory Ratio in Non-Dieting Individuals. Journal of Translational Medicine. 2012. 10(1), 237.

Tremblay, et al. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism. 1994 Jul;43(7):814-8.

Phelain JF, et al. Postexercise energy expenditure and substrate oxidation in young women resulting from exercise bouts of different intensity. Journal of the American College of Nutrition. 1997 Apr;16(2):140-6.

Carey, Daniel G. Quantifying Differences in the “Fat Burning” Zone and the Aerobic Zone. Journal of Strength and Conditioning Research. 2009. 23(7), 2090–2095.

Van Loon, L., et al. The effects of increasing exercise intensity on muscle fuel utilization in humans. Journal of Physiology. 2001. 536, 295–304.

Venables, M., et al. Determinants of fat oxidation during exercise in healthy men and women: a cross- sectional study. Journal of Applied Physiology. 2005. 98, 160–167.

Paoli, A., Marcolin, G., et al. Exercising Fasting or Fed to Enhance Fat Loss? Influence of Food Intake on Respiratory Ratio and Excess Postexercise Oxygen Consumption after a Bout of Endurance Training. International Journal of Sport Nutrition and Exercise Metabolism. 2011. 21(1), 48-54.

Sun, F., Wong, S., et al. Substrate Utilization During Brisk Walking is affected by Glycemic Index and fructose Content of a Pre-Exercise Meal. European Journal of Applied Physiology. November 2011. Published Ahead of Print

Cox, C., Stanhope, K., et al. Consumption of Fructose-Sweetened Beverages for 10 Weeks Reduces Net Fat Oxidation and Energy Expenditure in Overweight/Obese Men and Women. European Journal of Clinical Nutrition. September 2011. Published Ahead of Print.

Stephens, F., et al. Skeletal Muscle Carnitine Loading Increases Energy Expenditure, Modulates Fuel Metabolism Gene Networks and Prevents Body Fat Accumulation in Humans. The Journal of Physiology. 2013. 591.18, 4655-4666.

Gamze, E., et al. the Effects of Acute L-Carnitine Supplementation on Endurance Performance in Athletes. Journal of Strength and Conditioning Research. Published Ahead of Print.

Solomon, T., et al. A Low Glycemic Diet Lifestyle Intervention Improves Fat Utilization During Exercise in Older Obese Humans. Obesity. 2013. Published Ahead of Print.

Chan, H., et al. Oxygen Consumption, Substrate Oxidation, and Blood Pressure Following Sprint Interval Exercise. Applied Physiology, Nutrition, and Metabolism. 2013. 38(2), 182-187.

Yeo, W., et al. Fat Adaptation in Well-Trained Athletes: Effects on Cell Metabolism. Applied Physiology, Nutrition, and Metabolism. 2011. 36, 12-22.

Gonzalez, J., Stevenson, E. New Perspectives on Nutritional Interventions to Augment Lipid Utilization during Exercise. British Journal of Nutrition. 2012. 107, 339-349.