What Happens To Your Body If You Don’t Eat For 5 Days?

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What Happens To Your Body If You Don't Eat For 5 Days
What Happens To Your Body If You Don’t Eat For 5 Days? Graphic © healthpowerboost.com.
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Our relationship with food is at the heart of healthy living. What we eat, how we eat, and when we eat all play a role in our short-term and long-term health outcomes.

Fasting has long been a popular topic in health and fitness circles. But it is more than a fashionable trend. It’s an ancient practice – and there is scientific evidence to back it up.

Research shows that willingly reducing or abstaining from food for a period of time may offer numerous proven health benefits. This includes promoting blood sugar control, reducing inflammation, improving heart health, boosting brain function, aiding in weight loss, increasing growth hormone secretion, and even delaying aging. [1][2][3][4][5][6][7]

But how could the simple act of not eating affect the body in such profound ways? What happens to your body when you don’t eat?

Dr. Sten Ekberg, a holistic doctor and Olympic decathlete explores these questions by digging deeper into the mechanisms of fasting over a 5-day period. Here’s a detailed run-down of the changes to the body throughout a period of fasting.

First 12 Hours:

Few changes happen to your body during the first 12 hours. Your body transitions from the anabolic growth phase (or fed state)—where it digests and absorbs nutrients from the food you just ate—to the catabolic or early fasting stage.
During this phase glycogen (stored carbs), is broken down into glucose as blood sugar and insulin levels start to drop. [8] You also experience shifts in the levels of ghrelin and leptin, which are hormones responsible for stimulating hunger and regulating appetite, respectively. [9][10]

Towards the end of this phase, your body will gradually deplete glycogen stores and look into other energy sources (i.e., stored fats and proteins). “When you’re metabolically flexible, your body makes use of whatever fuel there is the most of,” Dr. Ekberg explains.

A key point to note is that the only form of energy your body can use is something called Adenosine triphosphate (ATP). Dr. Ekberg goes into detail explaining how everything that you eat eventually turns into ATP and how the body uses this molecule to power its processes.

18 Hours:

Past the 18-hour mark of fasting (or skipping breakfast), you’re more into the fat-burning mode. The body has burned through its glycogen reserve, and lipolysis is occurring. Triglycerides from fat cells are broken down into their constituent molecules for use as an alternative energy source. [11]

And as the body breaks down more fat stores and proteins for energy, the process releases ketone bodies at a measurable level. [12] As Dr. Ekberg points out, Ketones are not only fuel but also signaling molecules. They signal reduced inflammation and improved DNA repair, especially in the brain and nervous tissue.

Later on, the body will transition into a metabolic state known as ketosis, in which fat is the primary energy source. [13] Ketosis is not to be confused with the dangerous condition known as ketoacidosis. [14]

Your body also undergoes an increase in the secretion of human growth hormone (HGH) and brain-derived neurotrophic factor (BDNF), enhancing cognitive function and generating more elaborate neural networks. [6][15]

“At 18 hours, we start seeing just the beginnings of something called autophagy, which is a very interesting rejuvenation process in the body,” Dr. Ekberg says.

24 Hours:

As Dr. Ekberg explains, autophagy—one of the most powerful features of fasting—starts picking up speed after 24 hours of fasting. This is basically a ‘housekeeping’ survival mechanism whereby the body cleans up and recycles old or potentially dangerous cell parts. [16]

The production of AMP-activated protein kinase (AMPK) is triggered around this time, ramping up the autophagy and fat burning rate. [16]

Fasting also leads to the accumulation of NAD+. This is a potent molecule for signaling Sirtuins, which are survival genes while life-prolonging benefits. [17][18]

48 Hours:

After 2 days of fasting, the growth hormone levels may have increased by as much as 500%. [19] You will also experience increased BDNF and ketone levels as your rate of autophagy increases steadily.

Dr. Ekberg states: “Some more benefits we see at this time are brain repair, increased longevity, wound healing, and improved cardiovascular health.” [4][7][3] Other changes he points out include low insulin levels, low inflammation, and reversing aspects of metabolic syndrome. [1][2]

72 Hours:

If you don’t eat for 3 days, you will experience deeper levels of autophagy. This means more cleanup of debris/waste, including the misfolded proteins and other low-quality parts. The body gets picky—and as Dr. Ekberg illustrates, it says, “You know I need some resources. I need to build this thing over here, and this thing wasn’t perfect so let’s disassemble that and rebuild it.”

Dr. Ekberg also mentions that your body undergoes hematopoietic stem cell regeneration and rejuvenation. His claim is supported by a study conducted by researchers affiliated with the Panorama Research Institute and Regenerative Sciences Institute in California. [20] They found that prolonged fasting past the 72-hour mark stimulates the proliferation and rejuvenation of hematopoietic stem cells.

Some studies also suggest that cycles of starvation may increase the effectiveness of chemotherapy and delay tumor growth. [21]

120 Hours (5 Days):

Now, what happens if you don’t eat for 5 days? “There is nothing dramatically new that’s happening. But we are increasing the degree of everything that we talked about before,” Dr. Ekberg says. Think about increased fat burning and cleanup & repair (autophagy).

He also mentions that fasting for 120 hours gives your cells time to forget old set points or tendencies for things such as body weight—and instead create new ones.


Dr. Ekberg argues that healthy eating is about maintaining a balance between feast and famine. Our bodies need to experience periods where we load up and store some things—and we need to have other periods where we unload and burn some of the things we stored.

However, most people have lived most of their lives in the feast region, creating an imbalance in their bodies. They eat three or more meals and will never get past 12 hours of fasting. This means they never change their baseline markers for autophagy or ketones—and the profound health benefits that come with them.

“The [fasting] ranges I think would apply to most people is from 18 to 48 hours and then the 72 hours. So if you have reached most of your weight and health goals, you can absolutely make 18-hour fasting a lifestyle,” Dr. Ekberg concludes.

Video: https://www.youtube.com/watch?v=Wzmacu2TgFg
Topic: What Happens If You Don’t Eat For 5 Days?
Who? Dr. Sten Ekberg

Learn More: Health Benefits Of Fasting



[1] Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research, 164(4), 302-311: https://pubmed.ncbi.nlm.nih.gov/24993615/

[2] Kacimi, S., Ref’at, A., Fararjeh, M. A., Bustanji, Y. K., Mohammad, M. K., & Salem, M. L. (2012). Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects. Nutrition research, 32(12), 947-955: https://pubmed.ncbi.nlm.nih.gov/23244540/

[3] Beleslin, B., Ćirić, J., Žarković, M., Penezić, Z., Vujović, S., Trbojević, B., & Drezgić, M. (2007). The effects of three-week fasting diet on blood pressure, lipid profile and glucoregulation in extremely obese patients. Srpski arhiv za celokupno lekarstvo, 135(7-8), 440-446: https://pubmed.ncbi.nlm.nih.gov/17929537/

[4] Li, L., Wang, Z., & Zuo, Z. (2013). Chronic intermittent fasting improves cognitive functions and brain structures in mice. PloS one, 8(6), e66069: https://pubmed.ncbi.nlm.nih.gov/23755298/

[5] Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition reviews, 73(10), 661-674: https://pubmed.ncbi.nlm.nih.gov/26374764/

[6] Salgin, B., Marcovecchio, M. L., Hill, N., Dunger, D. B., & Frystyk, J. (2012). The effect of prolonged fasting on levels of growth hormone-binding protein and free growth hormone. Growth Hormone & IGF Research, 22(2), 76-81: https://pubmed.ncbi.nlm.nih.gov/22386777/

[7] Goodrick, C. L., Ingram, D. K., Reynolds, M. A., Freeman, J. R., & Cider, N. L. (1982). Effects of intermittent feeding upon growth and life span in rats. Gerontology, 28(4), 233-241: https://pubmed.ncbi.nlm.nih.gov/7117847/

[8] Stockman, M. C., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent fasting: is the wait worth the weight? Current obesity reports, 7(2), 172-185: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5959807/

[9] Abdalla, M. M. I. (2015). Ghrelin–physiological functions and regulation. European endocrinology, 11(2), 90: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5819073/

[10] Dornbush, S., & Aeddula, N. R. (2021). Physiology, Leptin. In StatPearls [Internet]. StatPearls Publishing: https://www.ncbi.nlm.nih.gov/books/NBK537038/

[11] Edwards, M., & Mohiuddin, S. S. (2020). Biochemistry, Lipolysis: https://www.ncbi.nlm.nih.gov/books/NBK560564/

[12] Puchalska, P., & Crawford, P. A. (2017). Multi-dimensional roles of ketone bodies in fuel metabolism, signaling, and therapeutics. Cell metabolism, 25(2), 262-284: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5313038/

[13] Zauner, C., Schneeweiss, B., Kranz, A., Madl, C., Ratheiser, K., Kramer, L., … & Lenz, K. (2000). Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. The American journal of clinical nutrition, 71(6), 1511-1515: https://pubmed.ncbi.nlm.nih.gov/10837292/

[14] Ghimire, P., & Dhamoon, A. S. (2021). Ketoacidosis. In StatPearls [Internet]. StatPearls Publishing: https://www.ncbi.nlm.nih.gov/books/NBK534848/

[15] Lee, J., Duan, W., Long, J. M., Ingram, D. K., & Mattson, M. P. (2000). Dietary restriction increases the number of newly generated neural cells, and induces BDNF expression, in the dentate gyrus of rats. Journal of Molecular Neuroscience, 15(2), 99-108: https://pubmed.ncbi.nlm.nih.gov/11220789/

[16] Glick, D., Barth, S., & Macleod, K. F. (2010). Autophagy: cellular and molecular mechanisms. The Journal of pathology, 221(1), 3-12: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2990190/

[17] Hayashida, S., Arimoto, A., Kuramoto, Y., Kozako, T., Honda, S. I., Shimeno, H., & Soeda, S. (2010). Fasting promotes the expression of SIRT1, an NAD+-dependent protein deacetylase, via activation of PPARα in mice. Molecular and cellular biochemistry, 339(1), 285-292: https://pubmed.ncbi.nlm.nih.gov/20148352/

[18] Imai, S. I., & Guarente, L. (2014). NAD+ and sirtuins in aging and disease. Trends in cell biology, 24(8), 464-471: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4112140/

[19] Hartman, M. L., Veldhuis, J. D., Johnson, M. L., Lee, M. M., Alberti, K. G., Samojlik, E., & Thorner, M. O. (1992). Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. The Journal of Clinical Endocrinology & Metabolism, 74(4), 757-765: https://pubmed.ncbi.nlm.nih.gov/1548337/

[20] Mendelsohn, A. R., & Larrick, J. W. (2014). Prolonged fasting/refeeding promotes hematopoietic stem cell regeneration and rejuvenation. Rejuvenation research, 17(4), 385-389: https://pubmed.ncbi.nlm.nih.gov/25072352/

[21] Lee, C., Raffaghello, L., Brandhorst, S., Safdie, F. M., Bianchi, G., Martin-Montalvo, A., … & Longo, V. D. (2012). Fasting cycles retard growth of tumors and sensitize a range of cancer cell types to chemotherapy. Science translational medicine, 4(124), 124ra27-124ra27: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3608686/

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