Evidence Based Muscle: FAT BURNING DOES NOT ALWAYS MEAN FAT LOSS [3 FAT LIPOLYSIS MYTHS!]

The process of losing fat involves the SUM RESPONSE of these changes over a prolonged time. Fat burning can occur temporarily, but if the sum response is not obtained over a prolonged period of time, fat loss will not occur. For fat loss to occur, you need to be mobilizing more fat than storing more fat in a chronic state.

A 2016 study put obese men on a high-carbohydrate, low-fat diet for 4 weeks and then switched them to a ketogenic, high-fat, low-carb diet for 4 weeks. Protein was the same for both diets. The researchers found that despite lower insulin levels, increased fat burning, and higher ketones on the ketogenic diet, there were no differences in body fat loss. (Hall et al., 2016)

FAT-BURNING EXERCISES 

You may have heard to burn more fat, you need to be in the fat-burning zone.  Fat-burning exercises are based on the heart rate zone. What is the fat-burning zone, you ask? Cardio zones are exercises at about 60-75% of your maximum heart rate.

During low-intensity exercise, your body burns more fat (i.e., fat-burning zone). However, during high-intensity interval exercise (HIIT), you train with a higher maximal heart rate and higher intensity, but your body burns less fat but more calories.

Studies have shown that HIIT and low-intensity exercise results in similar fat loss when calories are similar. (D’Amuri et al., 2021; Keating et al., 2017) Although low-intensity exercise increases fat mobilization acutely, this is not a sustained effect that occurs over 24 hours. (Harris & Kuo, 2021) High-intensity exercise results in fat loss despite not being in the fat-burning zone.

A study had overweight men perform cardio with either low-intensity or high-intensity exercise for 12 weeks. These subjects were not on a diet. They maintained their normal calories.

During low-intensity exercise, fat burning or fat oxidation increased by 40%. High-intensity exercise training did not affect fat oxidation during exercise. However, neither group had an increase in fat lipolysis at rest over 24 hours.

Thus, It was concluded that low-intensity exercise training in obese subjects seemed to increase fat oxidation during exercise but not at rest. (Aggel-Leijssen et al., 2002)

KEY POINTS: ACUTE FAT BURNING TEMPORARILY DOES NOT ALWAYS TRANSLATE INTO FAT LOSS.  Fat burning will not result in true fat loss if you are not in a calorie deficit.

DIETS

Calories intake is the master driver of losing fat. As discussed previously, when protein is the same, there is no difference between low-carb and low-fat diets for fat loss, despite low-carb diets burning more fat. (Stimson et al., 2007) (Hall et al., 2021)

This may be confusing; how can you burn more fat and not lose weight? The human body will use what you are consuming as its predominant fuel source.  If you eat a lot of carbohydrates, you will utilize carbs as your primary energy source. Vice versa, if you consume a high-fat diet, you will use fat as your primary fuel source.

If you consume more fat, more fats are available in the bloodstream, so more fat re-esterification occurs. So, you are burning more fat but also putting more fat into the cells. Conversely, if you follow a high carbohydrate diet, there will be reduced fat burning but less fat re-esterification, so less fat will go into the cell. So although both diets have different effects on fat mobilization and fat being deposited into the cell, the net effect is the same!

DO FAT BURNERS WORK?

Many so-called fat burners for women and men contain caffeine and other stimulants for an energy boost. Fat-burning ingredients are typically caffeine, green tea extract, synephrine, etc. A recent literature review found that fat-burning supplements were ineffective for fat loss.

Caffeine does increase fat mobilization, but the net effect on fat loss is very small without diet. Furthermore, intermittent fasting, paleolithic ketogenic diets, and other diets can increase fat burning. Still, the difference in calorie intake and calories burned during exercise will ultimately determine whether you are reducing fat cell size.  Fat loss is the chronic effect of being in a caloric deficit or when energy expenditure is greater than calorie intake.

REFERENCES

Aggel-Leijssen, D. P. C. V., Saris, W. H. M., Wagenmakers, A. J. M., Senden, J. M., & Baak, M. A. V. (2002). Effect of exercise training at different intensities on fat metabolism of obese men. Journal of Applied Physiology, 92(3), 1300-1309. https://doi.org/10.1152/japplphysiol.00030.2001

D’Amuri, A., Sanz, J. M., Capatti, E., Di Vece, F., Vaccari, F., Lazzer, S., Zuliani, G., Dalla Nora, E., & Passaro, A. (2021). Effectiveness of high-intensity interval training for weight loss in adults with obesity: a randomised controlled non-inferiority trial. BMJ Open Sport & Exercise Medicine, 7(3), e001021. https://doi.org/10.1136/bmjsem-2020-001021

Hall, K. D., Chen, K. Y., Guo, J., Lam, Y. Y., Leibel, R. L., Mayer, L. E., Reitman, M. L., Rosenbaum, M., Smith, S. R., Walsh, B. T., & Ravussin, E. (2016). Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. Am J Clin Nutr, 104(2), 324-333. https://doi.org/10.3945/ajcn.116.133561

Hall, K. D., Guo, J., Courville, A. B., Boring, J., Brychta, R., Chen, K. Y., Darcey, V., Forde, C. G., Gharib, A. M., Gallagher, I., Howard, R., Joseph, P. V., Milley, L., Ouwerkerk, R., Raisinger, K., Rozga, I., Schick, A., Stagliano, M., Torres, S., . . . Chung, S. T. (2021). Effect of a plant-based, low-fat diet versus an animal-based, ketogenic diet on ad libitum energy intake. Nat Med, 27(2), 344-353. https://doi.org/10.1038/s41591-020-01209-1

Harris, M. B., & Kuo, C.-H. (2021). Scientific Challenges on Theory of Fat Burning by Exercise [Hypothesis and Theory]. Frontiers in Physiology, 12. https://doi.org/10.3389/fphys.2021.685166

Keating, S. E., Johnson, N. A., Mielke, G. I., & Coombes, J. S. (2017). A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obes Rev, 18(8), 943-964. https://doi.org/10.1111/obr.12536

REFERENCES

Stimson, R. H., Johnstone, A. M., Homer, N. Z. M., Wake, D. J., Morton, N. M., Andrew, R., Lobley, G. E., & Walker, B. R. (2007). Dietary Macronutrient Content Alters Cortisol Metabolism Independently of Body Weight Changes in Obese Men. The Journal of Clinical Endocrinology & Metabolism, 92(11), 4480-4484. https://doi.org/10.1210/jc.2007-0692