Many diets focus on what to eat, but fasting focuses on when to eat. Two types of fasting include water fasting and intermittent fasting. 

During water fasting you consume zero calories. This can be done for several days. Water fasting is the most strict, but can reap the most rewards.  To learn more about water fasting and why we should all consider it at some point, we recommend this HBOT News Network podcast featuring Extivita’s medical director, Dr. Jay Stevens.

During intermittent fasting, eating is time-restricted and you cycle between periods of eating and fasting. Restricting calories for a certain number of hours each day or eating just one meal a couple days a week, or not eating for 24 hours once a week can all help your body burn fat and is linked to many various health benefits1. There are many different intermittent fasting schedules you could follow. 

Remember, during all fasting periods food is not allowed, but you can drink water, coffee, tea and other non-caloric beverages. 

 Stages of Fasting & the Impact on our Bodies 

All sorts of processes in the body change when we restrict our calorie intake, in order to allow our bodies to thrive during a period of famine. It has to do with hormones, genes and most importantly, cellular repair processes. Let’s dig a bit deeper into the different stages of fasting your body will go through. 

STAGE 1: Ketosis

Normally, after eating a meal, fats and sugars like glucose move from your stomach to your intestines, into your bloodstream, and eventually your cells. These cells use glucose for energy, but your cells do not use all these nutrients at once, and instead it is stored in your liver, muscles and fat tissue2. Once you begin your fast, our bodies will enter survival mode and use sugar stored away for energy. When the stored-up sugar begins to run low in our systems, the body looks for other sources of energy and begins to pull from the stored fat in our bodies. Our bodies will enter a metabolic state known as ketosis, 12 hours into your fast1. Ketosis is known as your body’s fat-burning mode, using stored fat for energy, and breaking down the fat in the body. 

STAGE 2: Heavy Ketosis

Once our bodies have used the energy from the stored fat, our livers begin to produce fatty acids known as Ketones3. Ketones are water soluble fat molecules which provide an alternative form of energy for the body when glucose reserves aren’t available.  Ketones offer many health benefits, helping your body fight stress and improving your memory and cognition4. An increase in Ketone levels can initiate cellular processes and even change gene expression to make you more resilient to stress5. In addition, ketones regulate and increase the production of proteins called BDNF, which promote an increase in new mitochondria and neuroplasticity. This ketone usage by your brain is one of the reasons that intermittent fasting is often claimed to promote mental clarity and positive mood. Ketones produce less inflammatory products as they are being metabolized and kick-start the production of the brain growth factor5. 

STAGE 3: Autophagy

Within 24 hours of your fast, damaged cells are being broken down and recycled for energy or formation of new proteins for the cell, pathogens like viruses and bacteria are also being destroyed6. This process is called autophagy: a type of cellular housekeeping, which has many potential health benefits.  Some of these benefits include neuroprotection, decreasing inflammation, protection from cancer, supports brain and cardiovascular health to name a few.  Autophagy is very important when it comes to aging and longevity7. Reduced autophagy has been associated with aging faster due to toxin accumulation8. 

STAGE 4: Peak Growth Hormone

Once you enter the 48-hour mark of fasting, your growth hormone level increases five times higher, than when you initially began the fast9. Growth Hormone is proven to positively impact the cardiovascular system. An increase in growth hormone will increase your blood flow, which as a result, improves your rate of wound healing10.

STAGE 5: Minimum Insulin

54 hours into your fast, your insulin will drop to the lowest level point, since your fast has begun. This significant decrease in insulin results in your body becoming insulin-sensitive11. Becoming insulin-sensitive is very important if you are at high risk of diabetes12. Not only does insulin sensitivity protect you from developing diabetes, but also reduces inflammation significantly and protects you from diseases, such as Cancer5.

STAGE 6: Immune Regeneration

Three days in your fast (approximately 72 hours), our bodies enter the immune regeneration stage. Our bodies begin to break down old immune cells and generate new and healthier cells13. Evidence shows that prolonged fasts lead to stress resistance, self-renewal and regeneration of hematopoietic or blood cell stem cells. In addition to this, prolonged fasting has been proven to preserve healthy white blood cell or lymphocyte counts in patients undergoing chemotherapy14. 

STAGE 7: Breaking a Fast

Now let’s discuss one of the most important stages of a fast, breaking your fast. It is important to fuel your body with a nutritious, balanced meal after your cells have regenerated into healthy, new cells. Your first meal should consist of plenty of vegetables, plant fibers and plant fats, healthy proteins and some whole grains or legumes. When breaking your fast, avoid foods with simple sugars and any processed or packaged foods14. 





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3Dąbek A, Wojtala M, Pirola L, Balcerczyk A. Modulation of Cellular Biochemistry, Epigenetics and Metabolomics by Ketone Bodies. Implications of the Ketogenic Diet in the Physiology of the Organism and Pathological States. Nutrients. 2020 Mar 17;12(3):788. doi: 10.3390/nu12030788. PMID: 32192146; PMCID: PMC7146425.   



6 Alirezaei M, Kemball CC, Flynn CT, Wood MR, Whitton JL, Kiosses WB. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010 Aug;6(6):702-10. doi: 10.4161/auto.6.6.12376. Epub 2010 Aug 14. PMID: 20534972; PMCID: PMC3106288. 

7Escobar KA, Cole NH, Mermier CM, VanDusseldorp TA. Autophagy and aging: Maintaining the proteome through exercise and caloric restriction. Aging Cell. 2019 Feb;18(1):e12876. doi: 10.1111/acel.12876. Epub 2018 Nov 15. PMID: 30430746; PMCID: PMC6351830. 


9 Hartman ML, Veldhuis JD, Johnson ML, Lee MM, Alberti KG, Samojlik E, Thorner MO. Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. J Clin Endocrinol Metab. 1992 Apr;74(4):757-65. doi: 10.1210/jcem.74.4.1548337. PMID: 1548337.

10 Caicedo D, Díaz O, Devesa P, Devesa J. Growth Hormone (GH) and Cardiovascular System. Int J Mol Sci. 2018 Jan 18;19(1):290. doi: 10.3390/ijms19010290. PMID: 29346331; PMCID: PMC5796235.

11 Klein S, Sakurai Y, Romijn JA, Carroll RM. Progressive alterations in lipid and glucose metabolism during short-term fasting in young adult men. Am J Physiol. 1993 Nov;265(5 Pt 1):E801-6. doi: 10.1152/ajpendo.1993.265.5.E801. PMID: 8238506. 

12 Gjedsted, Jakob & Gormsen, Lars & Nielsen, Søren & Schmitz, O & Djurhuus, Christian & Keiding, Susanne & Ørskov, H & Tønnesen, Else & Moller, Niels. (2007). Effects of a 3‐day fast on regional lipid and glucose metabolism in human skeletal muscle and adipose tissue. Acta physiologica (Oxford, England). 191. 205-16. 10.1111/j.1748-1716.2007.01740.x. 

13 Cheng CW, Adams GB, Perin L, Wei M, Zhou X, Lam BS, Da Sacco S, Mirisola M, Quinn DI, Dorff TB, Kopchick JJ, Longo VD. Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression. Cell Stem Cell. 2014 Jun 5;14(6):810-23. doi: 10.1016/j.stem.2014.04.014. Erratum in: Cell Stem Cell. 2016 Feb 4;18(2):291-2. PMID: 24905167; PMCID: PMC4102383.    

14 Mattson MP, Moehl K, Ghena N, Schmaedick M, Cheng A. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci. 2018 Feb;19(2):63-80. doi: 10.1038/nrn.2017.156. Epub 2018 Jan 11. Erratum in: Nat Rev Neurosci. 2020 Aug;21(8):445. PMID: 29321682; PMCID: PMC5913738.