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Intermittent Fasting and Stress

From Brad Pilon’s Eat Stop Eat Book

Fasting and Cortisol Cortisol is a corticosteroid hormone, or glucocorticoid, produced by the adrenal cortex, which is part of the adrenal gland. It is usually referred to as the "stress hormone" as it’s involved in your bodies response to stress and anxiety. Cortisol is released in response to various forms of stress (both physical and mental) as well as to low levels of blood glucocorticoid hormones. Its primary functions are to increase levels blood sugar through gluconeogenesis; suppress the immune system; increase blood pressure and aid in fat, protein and carbohydrate metabolism as a way to help your body deal with stress, illness, and injury (1). 

Cortisol is a lot like other ‘response systems’ in your body where acute increases are usually a good thing, helping you deal with stress, but chronically elevated or depressed levels lead to health problems. Cortisol has been fingered as a culprit in causing obesity, specifically through a speculative link to belly fat. And, of course, is been rumored that if you don't eat every couple hours you would cause your cortisol levels to increase. Comments like “If you don’t eat every couple hours your cortisol will get very high and it will ‘destroy’ your muscle mass”. The truth is cortisol secretion is vitally important to your overall health. Short periods of increased cortisol secretion are useful, such as the increased cortisol in the morning that helps liberate body fat to be used as a fuel, while prolonged cortisol increases may increase vulnerability to immunosuppression, and to autoimmune related and metabolic disorders (2). 

Since proper cortisol secretion is extremely important to overall health, it is definitely worthwhile examining how fasting affects cortisol. In direct opposition to the cortisol, the consistent finding in the research on fasting is that there is very little or no change in cortisol levels in response to a short period of fasting. This is true for both a short 24- hour fast (3) as well as after 72 hours of fasting (4). While research has shown that 5 straight days of fasting can cause a 1.8-fold increase in the 24-h endogenous cortisol production rate (5), It has also been found that even two weeks of fasting every other day (36-hour fasts) did not negatively affect cortisol levels.101 The funny thing is, we have known for more than four decades that increased cortisol is a phenomenon that is regularly found in obesity (6). And, that there is a direct correlation between the amount of body fat you have and your circulating cortisol levels. 

The inactive form of cortisol (cortisone) from the blood is converted to active cortisol by enzymes found in adipose tissue (7). This seems to be one of the mechanisms by which obesity can cause elevated cortisol levels. We have also known that treating obesity with very low-calorie diets causes a decrease in serum cortisol. So, being overweight increases cortisol, the actual act of fasting doesn't make it go up or down (at least when fasting for less than 72 hours), and losing weight will help return cortisol to normal? Sounds like even more reason to try short periods of fasting for weight loss. This isn’t to say that everyone’s cortisol levels are immune to weight loss. 72 hours of fasting has been found to increase cortisol levels in extremely lean (18% body fat) women, and chronic strenuous exercise has been shown to cause long terms increases in cortisol secretion (8). 

The truly amazing thing is that while delving into these common nutritional myths I began to find more and more health benefits that are associated with taking brief breaks from eating. It seems that fasting can have many positive health effects beyond simply helping you lose weight and burn body fat.More Information get the book at

If you need to lose weight and improve your health, please don't hesitate to contact us!

Pro-Holistic Care


  1. Hoehn K, Marieb EN (2010). Human Anatomy & Physiology. San Francisco: Benjamin Cummings. 
  2.  Munck A, Naray-Fejes-Toth A. 1994. Glucocorticoids and stress: Permissive and suppressive actions. Ann Eat Stop Eat 196 N Y Acad Sci 746: 115–130
  3. Gjedsted J, Gormsen L, Buhl M, Norrelund H, Schmitz, Keiding S, Tonnesen E, Moller N. Forearm and leg amino acids metabolism in the basal state and during combined insulin and amino acid stimulation after a 3- day fast. Acta Physiologica. 2009; (6): 1-9.
  4.  Soules MR, Merriggiola MC, Steiner RA, Clifton DK, Toivola B, Bremner WJ. Short-Term fasting in normal women: absence of effects on gonadotrophin secretion and the menstrual cycle. Clinical Endocrinology 
  5. Bergendahl M, Vance ML, Iranmanesh A, Thorner MO, Veldhuis JD.Fasting as a metabolic stress paradigm selectively amplifies cortisol secretory burst mass and delays the time of maximal nyctohemeral cortisol concentrations in healthy men. J Clin Endocrinol Metab. 1996 Feb;81(2):692-9. 
  6. Soeters MR. Intermittent fasting does not affect whole-body glucose, lipid, or protein metabolism. American Journal of Clinical Nutrition. 2009; 90:1244–51.
  7. Schteingart DE, Gregerman RI, Conn JW. A comparison of the characteristics of increased adrenocortical function in obesity and Cushing's Syndrome. Metabolism 1963; 1:261-85. 
  8. Morton NM. Obesity and corticosteroids: 11beta-hydroxysteroid type 1 as a cause and therapeutic target in metabolic disease. Mol Cell Endocrinol 2010; 316: 154-164 
  9. Jacoangeli F, Zoli A, Taranto A, et al, 2002 Osteoporosis and anorexia nervosa: relative role of endocrine alterations and malnutrition. Eat Weight Disord 7: 190-195.

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