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Written by Astrid Naranjo (Clean Health Accredited Clinical Dietitian)

If you want to understand how to optimize and reduce stubborn body fat, you have to understand a few key points.

First, let’s review the fat burning process. In order for fat to be lost from a particular area, there are few physiological steps that need to occur (1-3):

  1. Release/Lipolysis: Fat needs to be released from a fat cell (this process of fat breakdown and release is called “lipolysis”).
  2. Transportation: Fat needs to be carried to another cell through the blood stream (poor blood flow to an area means slow fat loss from an area).
  3. Oxidation: Fat needs to enter the mitochondria to be burned (lipid oxidation).

It is important to understand that the fact that fat is broken down and released (lipolysis), doesn’t necessarily mean it will be ultimately burned (lipid oxidation). It could be restored and this is often the case in people who are very insulin resistant or end up in calorie surplus.

For further in-depth explanation of the fat burning process check my previous article here.

One important thing to highlight in the fat burning process is the existence of 2 types of receptors in fat tissue called adrenergic receptors (AR).

Alpha adrenergic receptors and beta adrenergic receptors. The alpha receptors ( “a” for anti-burn) slow fat release and beta receptors (“b” for burn) speedy fat release.

In addition to having an impact on fat release directly, these receptors have an important correlation with blood flow. More alpha receptors may be associated with tissue that tends to receive less blood flow to an area, and more beta receptors may be associated with greater blood flow to an area.

So what makes fat ‘stubborn’? 

Well, stubborn fat has the characteristic that it can be impacted by a caloric deficit in some degree, but it will have a higher resistance to it compared to other types of fat (i.e visceral fat). Stubborn fat, may also be greater affected by certain hormones (for fat release or storage).

These hormones may have a direct or indirect effect on the enzymes and receptors on the adipose tissue. For instance, hormones that stimulate fat storage tend to increase the number or activity of alpha receptors and/or lipoprotein lipase (LPL), on the other hand, those that stimulate fat release, may increase the number or activity of beta receptors and/or hormone sensitive lipase (HSL) (1-2).

Catecholamines (adrenaline/epinephrine & noradrenaline/norepinephrine) speed fat release when they bind beta receptors, which would increase HSL activity. But they can also slow fat release when they bind alpha receptors. This is one of the reasons why stubborn fat, which has a higher concentration of alpha receptors, can be so slow to respond (2,3) .

Based on the literature, it appears that a greater adrenergic stimulus is required to overcome the lipolytic resistance in adipocytes with a higher density of alpha receptors. In these areas, epinephrine has been shown to exert an anti-lipolytic effect at lower concentrations, with the effect being reversed at higher concentrations (4-7).

Here are a important facts about stubborn fat in general & some hormonal effects to keep in mind:

1. Stubborn fat has more alpha receptors and less beta receptors

2. Stubborn fat tends to have less blood flow through it.

3. Hormones that increase HSL activity and/or inhibit LPL activity stimulate fat release

4. Hormones that decrease HSL activity and/or stimulate LPL action encourage fat storage

5. Energy balance matters a lot. It is impossible to store fat regardless of hormonal action in a calorie deficit and it is unlikely to lose fat if you are in a calorie surplus

6. Stubborn fat is stubborn not because it can’t be released, but rather because it releases fat in a much more slower rate compared to other areas of stored fat.

7. The most stubborn fat on the body is the fat under your skin, the subcutaneous fat ( as it is more reactive to insulin, has lower blood supply and may have more alpha receptors)

8. Subcutaneous fat is far more stubborn compared to visceral fat (since visceral fat may have more beta receptors and greater blood flow)

9. Female subcutaneous fat is more stubborn compared to male subcutaneous fat.

10. The most stubborn fat in the majority of women is lower body subcutaneous fat around the hip, glutes and thighs (also called saddle bags, thunder thighs or bubble butts). The most stubborn fat on men is the subcutaneous fat of the lower abdomen (often called the love handles)(12)

Possible solutions include:

1. Nutrition is key
Plan your diet in a way that allows you to have periods of more food and more exercise with periods of less food and less exercise. This helps build muscle and burn fat (or at least maintain it) and mitigates metabolic adaptation.

2. Target the area
Use targeted exercise and lifestyle strategies to suppress and/or bypass the alpha receptors and elevate the beta receptors to increase fat release from stubborn areas(8,9). Exercise has been shown to increase norepinephrine and epinephrine in an intensity-dependent manner (8,9). An exercise intensity greater than 70% of VO2max may be required to overcome the lipolytic resistance of adipocytes with a higher density of alpha-2 receptors.

However, once the intensity exceeds 80% of VO2max, fatty acid oxidation drops drastically (10). That’s because muscles preferentially use glucose instead of fatty acids during high intensity exercise. If the fatty acids that have been liberated from a high intensity bout are not oxidized shortly after, they will be re-esterified back into the fat cells (8-11).

A better strategy for burning stubborn body fat would be to perform a bout of high intensity exercise to maximize lipolysis followed by a bout of low intensity exercise to oxidize the fatty acids that have been releases into the blood stream, before they are re-esterified.

One study found that when low intensity aerobic exercise was performed after a bout of resistance exercise, fat oxidation was greater than when the aerobic exercise was performed alone (13). Preceding aerobic training with high intensity interval training (HIIT) would likely be even more effective in that regard due to the greater catecholamine(14).

3. Use of supplements
Using stimulants can aid bypassing, inhibiting or blocking the alpha receptors. This includes supplements/substances such as yohimbine HCL, caffeine and Green tea extract (GTE)(15-19).

Conclusion
As you can now appreciate, there is more to fat loss than just creating a calorie deficit, especially when it comes to targeting stubborn body fat in certain areas. Due to the different receptors on adipocytes, namely the alpha and beta adrenergic receptors, it is harder to mobilize fat from certain parts of the body (women tend to struggle more than men).

Hence, if you are already quite lean, but there are certain areas than take long to lean down, all the strategies mentioned in this article may help you to enhance the stubborn fat mobilization & oxidation.

To learn more about optimizing fat loss for your clients, click here to enrol into the Performance Nutrition Coach Collection!

References

  1. Horowitz, J.F, and Klein, S. (2000.) Lipid metabolism and endurance exercise. American Journal of Clinical Nutrition. 72 (suppl), 558S-563S.
  2. Venables MC1, Achten J, Jeukendrup AE. Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. J Appl Physiol 2005 Jan;98(1):160-7.
  3. Duncan, R.E, Ahmadian, M., Jaworski, K., Sarkadi-Nagy, E., & Sul, H.S. (2007). Regulation of lipolysis in adipocytes. Annual Review of Nutrition. 27, 79-101
  4. Mauriège P, Galitzky J, Berlan M, Lafontan M. Heterogeneous distribution of beta- and alpha2-adrenoceptor binding sites in human fat cells from various fat deposits : functional consequences. Eur J Clin Invest 1987 ; 17 : 156-165.
  5. Mauriège P, Després JP, Prud’homme D et al. Regional variation in adipose tissue lipolysis in lean and obese men. J Lipid Res 1991 ; 32 : 1625-1633.
  6. Mauriège P, Prud’homme D, Lemieux S, Tremblay A, Després J-P. Regional differences in adipose tissue lipolysis from lean and obese women : existence of postreceptor alterations. Am J Physiol 1995 ; 269 : E341-E350.
  7. Mauriège P, Imbeault P, Langin D et al. Regional and gender variations in adipose tissue lipolysis in response to weight loss. J Lipid Res 1999 ; 40 : 1559-1571
  8. V. Stich, F. Marion-Latard, J. Hejnova, N. Viguerie, C. Lefort, H. Suljkovicova, D. Langin M, Lafontan M, Berlan. Hypocaloric Diet Reduces Exercise-Induced α2-Adrenergic Antilipolytic Effect and α2-Adrenergic Receptor mRNA Levels in Adipose Tissue of Obese Women, The Journal of Clinical Endocrinology & Metabolism, Volume 87, Issue 3, 1 March 2002, Pages 1274–1281
  9. Giovannitti JA Jr, Thoms SM, Crawford JJ. Alpha-2 adrenergic receptor agonists: a review of current clinical applications. Anesth Prog. 2015;62(1):31–39. doi:10.2344/0003-3006-62.1.31
  10. Polak J, Bajzova M, Stich V. Effect of exercise on lipolysis in adipose tissue. Future Lipidology. 2008; 3:5, 557-572
  11. LaForgia J, Withers RT, Gore CJ. Effects of exercise intensity and duration on the excess post-exercise oxygen consumption. J Sports Sci. 2006 Dec;24(12):1247-64
  12. Moro C, Pillard F, de Glisezinski I, Crampes F, Thalamas C, Harant I, Marques MA, Lafontan M, Berlan M. Sex differences in lipolysis-regulating mechanisms in overweight subjects: effect of exercise intensity. Obesity (Silver Spring). 2007 Sep;15(9):2245-55.
  13. Goto K, Ishii N, Sugihara S, Yoshioka T, Takamatsu K. Effects of resistance exercise on lipolysis during subsequent submaximal exercise. Med Sci Sports Exerc. 2007 Feb;39(2):308-15.
  14. Barnes PJ. Beta-adrenergic receptors and their regulation. Am J Respir Crit Care Med. 1995 Sep;152(3):838-60.
  15. Shi D, Nikodijević O, Jacobson KA, Daly JW. Chronic caffeine alters the density of adenosine, adrenergic, cholinergic, GABA, and serotonin receptors and calcium channels in mouse brain. Cell Mol Neurobiol. 1993;13(3):247–261. doi:10.1007/bf00733753
  16. Norager CB, Jensen MB, Weimann A, Madsen MR. Metabolic effects of caffeine ingestion and physical work in 75-year old citizens. A randomized, double-blind, placebo-controlled, cross-over study. Clin Endocrinol (Oxf). 2006;65(2):223–228. doi:10.1111/j.1365-2265.2006.02579.x.
  17. Astrup A, Toubro S, Cannon S, Hein P, Breum L, Madsen J. Caffeine: a double-blind, placebo-controlled study of its thermogenic, metabolic, and cardiovascular effects in healthy volunteers. Am J Clin Nutr. 1990;51(5):759–767.
  18. Ostojic SM. Yohimbine: the effects on body composition and exercise performance in soccer players. Res Sports Med. 2006;14(4):289–299. doi:10.1080/15438620600987106.
  19. Ostojic SM. Yohimbine: the effects on body composition and exercise performance in soccer players. Res Sports Med. 2006 Oct-Dec;14(4):289-99. doi: 10.1080/15438620600987106. PMID: 17214405.

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