What Are The Hourly Benefits Of Fasting?

It’s an established fact that going without food is therapeutic. What you may not know is the hour-by-hour benefits of fasting. For instance, what are the hourly benefits of fasting for six hours, 16 hours, or 48 hours, in terms of its impact on blood sugar, insulin, liver glycogen, human growth hormone, fat burning, glucagon, and the magical process of autophagy? Stay with me as I break down the process.

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The Process Of Fasting

Here’s a brief overview of what happens physiologically when you fast. The human body runs on energy. Energy is needed both in a fasted and non-fasted state. The body’s main energy source is glucose, which is abundant in carbohydrates. Both the liver and muscles store glucose in the form of glycogen.

This stored glucose is a secondary energy source, and is what enables you to sleep through the night without needing to eat. Approximately 1200 calories of glycogen are stored in the muscular system and liver. The liver stores simple sugars, whereas, complex carbohydrates are stored in the muscle. How much glycogen you’re able to store is in direct correlation to how much muscle mass you have.

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Glycogen Depletion

When glycogen becomes depleted, the body transitions into a fasted state. Energy is then created via a process called gluconeogenesis, whereby energy is made using protein and fat. Since no glucose is coming in, energy must still be made, and with glycogen no longer available, fat becomes the preferred energy source. This is why weight loss is a welcomed side effect of fasting.

Over time, when fat can no longer be used, the body eventually enters starvation mode, which causes the metabolism to slow down. The body then resorts to burning muscle for fuel. This scenario typically happens after weeks of fasting. My preferred method of fasting is intermittent fasting, which is more sustainable and strategic than traditional fasting. The OMAD diet is another method of fasting where just one meal a day is eaten. Read my posts below to learn more:

[Read More: Human Growth Hormone and Intermittent Fasting]

[Read More: 7 Reasons To Consider the OMAD Diet]

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Human Growth Hormone

Human growth hormone (HGH), secreted from the pituitary gland, is responsible for regulating growth and body composition, protein synthesis, fat-burning, muscle and bone growth, and fat and sugar metabolism. It regulates the growth of every cell in the body. It is the hormone associated with youth, and like other hormones, declines with age.

Low levels of human growth hormone lead to reduced muscle mass, increased body fat, reduced bone density, insulin resistance, cardiovascular problems, anxiety and depression, low-exercise tolerance, fatigue, and insomnia. Essentially, it manifests as the symptoms associated with aging. Increased levels of HGH improve body composition, stabilize mood, boost energy, and optimize immune function. HGH is the ultimate fat burner and its production increases during fasting.


Ketosis is a metabolic state characterized by high levels of ketones in the blood. Ketones are made in the liver and are produced when insulin levels are low, and when glucose can’t be used for energy. Ketosis can be achieved by restricting carbohydrates to under 50 grams a day or by fasting. In this state, energy is created by burning stored body fat, rather than burning glucose for fuel.

With carbohydrates so plentiful, most people rarely enter ketosis, an adaptive metabolic pathway used in times of scarcity when sources of glucose aren’t available. Ketosis is a normal state of metabolism with ketones providing a reliable alternate energy source.

There are many variations of the ketogenic diet, just as there are numerous ways to intermittent fast. The benefits of ketosis include hormone and blood sugar regulation, increased fat-burning, appetite suppression, better oxygen utilization, the preservation of muscle glycogen, increased mental focus, and better physical performance.


Authophagy is a hot topic. In fact, the Nobel Prize in medicine was awarded for work on autophagy, which means “self-eating” or “self-consuming.” And that’s exactly what autophagy does, it recycles old, damaged, and diseased cellular components so they can be reused. Worn out cells need to be replaced for systems in the body to function optimally. This recycling process is stimulated by fasting as the body cannot “self-eat” when food is coming in.

Benefits of autophagy include: increased insulin sensitivity, eradication of pathogens, increased detoxification, reduction in progression of degenerative diseases, such as Alzheimer’s, Parkinsons, and even cancer, due to its favorable effect on tumor progression. Autophagy retards aging, reduces inflammation, boosts stem cell production, balances hormones, increases growth hormone, and improves immune function. Notably, brain tumors have been shown to regress from autophagy.

Autophagy is stimulated by fasting for at least 16 to 20 hours. For the process to be activated, glycogen stores need to be depleted and ketosis induced. All excess calories must be burned before autophagy kicks in. The number of calories previously consumed will be a determining factor as to when the process begins. Exercise, and movement of all types, accelerates glycogen depletion as will implementing a ketogenic diet.


Glucagon is a fat-burning hormone secreted by the pancreas that opposes the effects of insulin. Insulin is secreted by the beta cells within the gland, whereas, glucagon is released from the alpha cells.

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The actions of insulin and glucagon work in tandem to keep blood sugar levels stable. The role of glucagon is to raise the concentration of fatty acids and glucose in the blood when insulin levels are low. Elevated insulin levels, on the other hand, prevent the release of fat.

When glucagon is elevated, glycogen in the liver is mobilized. Glucagon induces lipolysis, the mobilization and breakdown of stored energy, when levels of insulin are low. It increases the expenditure of energy, and is raised during times of stress, such as fasting.

The Hourly Benefits Of Fasting

Here are some of the tremendous benefits of fasting that are broken down into specific time increments:

4 to 6 Hours

At the four-hour mark, all food has left the stomach. Blood sugar is decreasing, as well as insulin, which is no longer produced in the absence of glucose. If you consistently spaced your meals every four hours, instead of eating every two like many people do, you would regulate your hormones and body weight.

8 Hours

After eight hours of fasting, glycogen reserves are depleted. Gluconeogenesis is initiated as the body enters a fasted state. Since glucose is no longer available, the liver converts protein and fat into energy. Calorie-burning is accelerated, the basal metabolic rate slows, and the body becomes more efficient at using available energy. Due to this reduction in metabolic rate, blood pressure and heart rate both decrease.

12 Hours

The body enters a healing phase after 12 hours without food. The digestive system begins to rest as there are no calories to burn. Levels of human growth hormone ramp up, and glucagon is secreted from the pancreas to keep blood sugar levels within the normal range.

14-18 Hours

At this point in the fasted state, the body begins to convert fat into glucose for energy. Human growth hormone continues to rise significantly as fat-burning continues. The most incredible benefit of fasting is the cellular clean-up process of autophagy, which is mildly induced around the 16-hour mark. This is when things start to get good.

Precisely when autophagy is activated will depend on several factors, such as, how many carbs and how much protein were eaten at the last meal, if exercise was part of the picture, and if any fruit was consumed. Fruit contains fructose which replenishes glycogen stores.


Fasting Duration Benefits
4 – 6 hours Reductions in blood sugar and insulin
8 hours Glycogen reserves are depleted, gluconeogenesis is initiated, the liver converts protein and fat into energy
Calorie burning is accelerated, basal metabolic rate slows, blood pressure and heart rate both decrease
12 hours A healing phase is initiated, the digestive system begins to rest, levels of HGH ramp up
Glucagon is secreted from the pancreas to keep blood sugar levels within normal range
14 – 18 hours Fat is converted into glucose for energy, HGH continues to rise as fat-burning continues
The cellular clean-up process of autophagy is induced around the 16-hour mark
24 hours Autophagy takes off, toxin-elimination ramps up, fat-burning is in full swing as HGH increases
Insulin decreases, ketones are released, lipolysis is induced
36 hours Autophagy skyrockets, HGH production increases, fat-burning and toxin-elimination continue
Insulin continues to drop, while lipolysis increases
48 hours Autophagy increases unabated (up to 30%), the immune system begins to repair and regenerate
The inflammatory process is reduced, lipolysis is maintained, cellular toxins are released
72 hours Autophagy continues to work its magic and accelerates up to five fold due to calorie-restriction
and reduced insulin levels

24 Hours

The incredible process of autophagy really takes off at the 24-hour mark. Toxin-elimination also ramps up. Fat-burning is in full swing thanks to the rise in HGH and the decrease in insulin. Ketones, an efficient source of energy from fat, are released. The more insulin sensitive a person is, the faster lipolysis will be induced, which underscores how critical exercise and its insulin-lowering effects are.

36 Hours

The cellular clean-up, repair, and renewal process of autophagy continues to skyrocket. HGH production, fat-burning and toxin-elimination continues due to the drop in insulin and boost in lipolyis. Reducing levels of insulin is very significant, but so is the amount of time that levels remain low. This is why longer fasts yield such amazing results. Autophagy cannot be activated in the presence of insulin.

48 Hours

Autophagy progresses unabated, accelerating up to 30% or more. After two days without food, the immune system begins to repair and regenerate. The inflammatory process is notably reduced as lipolysis is maintained. Toxins continue to be released as damaged molecules within the cells are broken down.

72 Hours

Autophagy continues to work its magic. Many of the benefits attributed to calorie-restriction stem from autophagy. The lower the levels of insulin are, the higher the rate of autophagy, which after three days of fasting can increase up to five fold. Like many other processes in the body, autophagy declines with age.

As the rate of autophagy slows, cellular debris begins to accumulate. Insulin resistance, which is epidemic in today’s society, accentuates the problem by further inhibiting autophagy. This reduced rate likely accounts for many of the negative effects of obesity and diabetes. Fasting is a fantastic way to reset autophagy. Keep in mind, if you’re going to fast for 72 hours, once a season is enough.

Detoxification Reactions

Autophagy and toxin-release can create a detox or Herxheimer’s reaction. Binders and clays can be helpful for mopping up mobilized toxins before they can be recirculated. Common detox reactions may include headaches, joint pain, skin rashes and breakouts, irritability, insomnia, and fatigue.

If you experience any of these symptoms, step up your detox strategies. Colonics, coffee enemas, rebounding, exercise, epsom salt baths, and saunas are all effective methods to eliminate toxicity. Also, drink plenty of filtered water to stay hydrated and foster the release of toxins.

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Key Points

Aging is the result of the body’s inability to repair and recycle. When damage accumulates, the signs of aging become visible. Fasting, through the stimulation of autophagy, can reset the rate at which the body is able to repair and heal. There’s not a better strategy to look and feel younger longer.

What are your experiences with fasting? Did you know many of its beneficial effects are attributed to autophagy? Let me know in the comments:)


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(1) Medical News Today: What happens if you fast for a day?

(2) NCBI PubMed.gov: Autophagy: cellular and molecular mechanisms

(3) Cell.com: Autophagy in the Pathogenesis of Disease

(4) Siim Land: Do You Get Autophagy Fasting for 16 Hours?

(5) WebMD: Human Growth Hormone (HGH)

(6) Kingsberg Medical: What Happens If You Do Not Produce Enough HGH?

(7) WebMD: What are ketones?

(8) Perfect Keto: The Ultimate Guide To Ketosis


Disclaimer: “I am not a medical doctor, and therefore, cannot diagnose or treat any medical condition, nor do I claim in any way to cure disease. Please be diligent and always do your own research in regard to any material I present on this site. I claim no responsibility for any distress, whether it be physical or emotional, that may occur as a result of the information you obtain from my blog.”

15 thoughts on “What Are The Hourly Benefits Of Fasting?”

  1. These are really interesting facts on how glucose is stored and used. Now I understand how we are able to sleep the entire night without needing to wake up to eat. I have never really looked at fasting in terms of hour by hour benefits.. Your breakdown is well elaborated. 

    I think I can comfortably fast for around eight hours. I just love that calorie burning is increased at this stage. Works for me as I need to lose the weight. Thank you for this thorough explanation. Very enlightening article.

    • Thank you Carol,

      Human biochemistry is so interesting, and the mechanisms that keep us healthy, like being able to sleep through the night without having to consume calories. Knowing what the benefits of fasting are, in terms of duration, is fascinating. 

      I can easily fast for 14-16 hours, but it did take awhile to get used to it. Now for the most part it doesn’t bother me. There’s nothing better than intermittent fasting for losing unwanted pounds. Thanks for your comment:)

  2. Nice and informative article about the effects of fasting. I have been on the keto diet since 2006 when it was here in Scandinavia, but was considered dangerous and a “habit of some 80´s fitness guys.” Most of the doctors warned about harsh consequences I will face if I didn’t stop eating saturated fats from fatty beef and so on. 

    I have been getting some of these effects by ketosis but I have also tried some small fasting routines and it feels like I start to shrink. Do you have links or recommendations about some good nutrition advice for fasting? However, I added your site as a bookmark. 

    • Hi Jesse,

      Thank you. That’s interesting the Keto diet was considered dangerous. The effects of obesity, insulin resistance, and diabetes, the conditions the diet are good for, are far more harmful than reducing carbohydrates will ever be. Here is an article you might find helpful.

      Thanks for reading and taking the time to comment:)

  3. Great info
    I have 2 weeks on Omad diet
    I am obese and already have dropped
    7 kilos. I feel great….
    Thanks for the share!!!

  4. I am underweight with a BMI of below 18. I have always been thin and have a hearty appetite. I can fast for up to 12 hours but wouldn’t like to try more as I really don’t want to lose weight. So I don’t think I have the courage to try long fasts of more than 16 hours.

    • You’re doing intermittent fasting? How long have you been doing it? It may take awhile for your blood sugar to come down if it was elevated. If you’ve been unusually stressed lately, it could be that your cortisol levels are high, which will raise blood sugar. If you haven’t been fasting for very long, I would just keep at it and retest.

  5. Thanks for taking the time to write this article – I have found this page to be very informative!

    I have a question:
    I am to undergo a minor surgery soon (I will be under general anaesthetic) and I am considering fasting for 36-72 hours beginning from the time I have been told to stop eating prior to the surgery and finishing a day or two after the the surgery. I have read a lot of peoples’ opinions on the matter, most saying ‘NOOOO’ to fasting and post-surgery recovery, however, considering that prolonged fasting enables the body to rid itself of toxins and dead cells, allowing the body to heal itself, surely it makes complete sense to fast before, during and after the operation so my body can focus on healing my wounds?

    So my thoughts are: fast before, during and after the surgery to give my body time to focus on biological repairs. Or, if that sounds like an unadvisable idea to you guys, how about fasting for a prolonged time a week post-surgery? Or not fast at all?

    Any help will be greatly appreciated! Thank you in advance :)

    • I should also add that I have been intermittently fasting (between 16-20 hours most days) since March. And I completed a 40 hour fast this morning.

    • Thank you. I appreciate that. I can see your reasoning for fasting. In my opinion, however, 72 hours is probably too long as you’ll need nutrient-intake to preserve your strength. You also need protein, which helps build and repair tissue. I would do a 24-hour fast and then continue with your intermittent fasting. That way, you’ll still be getting your nutrients and protein, but still get to take advantage of autophagy.

      If you’ve been intermittent fasting since March, I’m sure you’ve already stimulated autophagy. Your cells should be pretty darn healthy at this point. Do make sure and stay well hydrated. I always sprinkle some Himalayan sea salt in my water to boost hydration, and to add extra minerals to my diet. I would wait at least a couple of weeks to do a prolonged fast. Surgery is a significant stress on the body so please concentrate on nourishing it well!

      Best of luck to you!

      • Thank you for taking the time to respond to my question.

        I will take your advice and fast for 24 hours. Then in a few weeks I’ll try a prolonged fast. Thanks again for your help (and for the Himalayan sea salt tip) – it is really appreciated! :D


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