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The Five Fundamental Stages of Fasting

The Five Fundamental Stages of Fasting

by Tom Davis -

Missing meals and foregoing carbs is a foolproof approach to rapidly deplete your glucose stores, encourage ketosis, and torch excess body fat, but the benefits of fasting for health go far beyond skin deep.

Aside from accelerating fat loss, fasting enhances immune function, boosts muscle building, and supports mental clarity and a well-balanced mood—all being potent results from a fairly simple practice.

However, while all fasting offers impressive health benefits, the depth and breadth of those outcomes may vary vastly based on the duration you temporarily part with the plate.

Whether you want to shed a little excess weight or seek to promote cell autophagy and renewal, there's a fast to assist in meeting your goal. Besides, pairing a ketogenic diet with the structure of timed feeding windows is a potent approach to maximize vitality and overall results.

Leveraging the power of fasting is a fantastic way to ratchet up your health and wellness—something on the minds of many—and knowing what to expect at various stages of refraining from food is critical to assist you in achieving your intended goals when abstaining from calories.

Here’s more about the five main stages of fasting, the unique benefits associated with each one, and a quick note on how to integrate the power of fasting into your keto lifestyle:

Stage 1 Fasting (8-12 Hours): Stable Blood Sugar

The body enters a fasted state about eight hours after your last meal. As a result, blood sugar levels tend to dip in the initial phase of foregoing food, and you may notice fatigue, trouble concentrating, and sparked food cravings during this initiation phase.

Fortunately, similar to the keto flu, the preliminary side effects of fasting pass somewhat quickly, and symptoms should subside around the twelfth-hour mark.

After 12 hours, your body begins to tap into your glycogen (sugar) stores, and your blood sugar levels start to return to equilibrium. Around this time in your fast, your metabolism shifts toward ketosis as you continue to restrict sugar (and all caloric) intake.

Your body realizes that its usual glucose supply is dwindling and efficiently seeks out ketones and fat in the body to use for energy in its place.

A fast for 8-12 hours is considered a short-term option. And committing to these brief periods without food may lower blood pressure and improve insulin sensitivity or other matters of blood sugar control, as well.

Stage 2 Fasting (12-18 Hours): Ketosis, Fat Burning, and Mental Clarity

Your body should achieve metabolic ketosis between hours 16 and 18 of fasting, with your brain, heart, and muscles now running on the fat and ketones derived from your body's fat stores as well as the foods and beverages you consume.

Your body now defaults to the liver producing enhanced ketone bodies to act as the primary power source for all of your bodily functions and processes. And you're on the road to condition your body for better metabolic flexibility and efficiency associated with optimal glucose regulation.

Plus, the benefits continue in this fasting phase to include appetite suppression, increased mental clarity, and fat loss.

Appetite Suppression

Many people struggle to curb cravings and an insatiable desire to eat their favorite foods that no longer serve them. Still, something powerful occurs when we venture deeper into fasting: appetite suppression.

Ravenous cravings and thoughts of raiding the fridge or pantry with reckless abandon should subside now, and feelings of satiety despite not consuming calories are common.

Feeling like you've hit your stride and even sensing an increase in energy or mental sharpness are hallmarks of this more extended fasting period.

Fat Loss

Forcing the body to devour our fat stores after our glucose supply depletes is a fantastic way to incinerate excess fat as the body converts it to preferred energy in the form of endogenous ketones.

Without consuming calories for energy, our systems switch to full-on fat-burning mode and torch maximum calories with the body in a fasted state—literally using the fat you desire to lose to provide increased energy and mental sharpness!

Plus, this fasting phase triggers the hunger-regulating hormone ghrelin, which informs the body that it's time to eat and how much while stabilizing blood sugar and insulin levels, resetting your natural hunger levels.

Using a fasting timeline of 16-18 hours a day works well for those intermittent fasting daily or several times a week. Implementing a 6-8 hours feeding window helps naturally curtail the appetite while assimilating the food consumed most efficiently.

Mental Clarity

Protein is a cornerstone of building and repairing muscle, and strains of proteins created during fasting, like brain-derived neurotrophic factor (BDNF), provide added protection to existing brain cells while promoting the growth of new healthy brain pathways.

Plus, the increase of BDNF supports healthy brain function to aid in learning and keeping the mood balanced—a benefit present in those who fast and enter a state of metabolic ketosis.

Thankfully, several benefits of fasting and ketosis—like appetite suppression, mental clarity, and mood regulation—intensify when paired because of their compounded symbiotic effect on one another.

Stage 3 Fasting (24 hours): Autophagy and Anti-Aging

After a full day of rest from the business of digestion and nutrient assimilation, the body enters a powerful reparative state of autophagy where it identifies and discards old or potentially rogue cells that could result in disease—replacing them with new healthy cells.

If you're turning down your plate seeking access to the fountain of youth or a tool to reduce inflammation and oxidative stress in the body to thwart degenerative illness, a day-long fast may be the best approach to take.

A fast of this duration is also ideal for the slightly-seasoned faster, who may already be intermittent fasting throughout the week. Acclimating the body to shorter fasts first helps make extended sessions much easier to execute with ease.


Stress gets a bad reputation for its destructive properties, but mild stress—like that caused by light exercise and even inflammation—aid in repairing the body.

We cannot overstate the importance of autophagy in the body's well-being and defense against disease. When the body functions well, it naturally eliminates damaged cells and fortifies areas in our immunity to maintain or enhance health.

Furthermore, the benefits of fasting-induced autophagy have shown promising effects in studies as follows:

  • Gifts of autophagy to the brain include eliminating specific proteins associated with disorders like Alzheimer's disease and dementia.
  • The body's natural cycling of autophagy slows as we age. As a result, we significantly boost our health and vitality by triggering this cleansing and renewing cellular process with extended periods of fasting.
  • Giving the body a chance to rest and recuperate from all the effort expended during digestion reduces inflammation and oxidative stress in every body system, making us inhospitable to illness and disease.

Stage 4 Fasting (36-48 hours): Growth Hormone and Recovery

Once you get your feet wet in the world of intermittent fasting, you may decide you're ready to enter the league of longer-term fasting between 36 and 48 hours.

As you prolong your fast for more consecutive days, your growth hormone levels are affected in ways that offer the body an increased range of health benefits.

Muscle Growth and Repair

Fasting is shown to significantly increase human growth hormone (HGH) and generally results in enhanced bursts of elevated levels of HGH disbursed in the body throughout the day.

Sounds reasonable enough, but what does increased HGH levels mean concerning your well-being? Well, we're so glad you asked because the answer is very hopeful.

Fasting increasing HGH production matters because higher hormone levels contribute to quicker muscle repair and elevated levels of muscle mass—which are particularly essential as we age. Plus, elevated HGH may quicken the healing process for wounds and other injuries.

Plus, adding and maintaining lean mass is vital as we mature to help prevent injuries and fractures while enabling us to live as active a life as we desire.

Fortunately, although it may appear a metabolic paradox, turning away from food for a few days can aid in gaining lean muscle, not contribute to losing it.

The body will assimilate the proteins consumed more efficiently after the reset provided during an extended fast, improving the muscle repair and recovery process—even lessening the intensity and duration of recovery between intense forms of fitness.

Stage 5 Fasting (72+ hours): Stem Cells and Immune Function

The final phase of fasting starts after going three consecutive days without food. However, it's important to note that fasting for this long is a serious undertaking and one to do under medical supervision and with clearance from your doctor, especially if you have type 2 diabetes or other metabolic disorders.

Also, it's important to sip on lots of water and consume significant amounts of electrolytes—like sodium, magnesium, and potassium—to replenish lost fluids, vitamins, and minerals throughout the day.

Most importantly, listen to your body during an extended or any duration fast. Don't dismiss feeling lightheaded or otherwise unwell; stop the fast if you're entirely zapped of energy or feel sick and consult your physician.

Immune System Regeneration

Fasting's link with improved immune function is hopeful. Plus, the benefits of fasting multiply when you abstain from eating for 72 hours—triggering new stem cell production and creating spanking new healthy cells to replace old, dysfunctional, or damaged ones.

Also, a 2014 study that shared results related to the boosted immunity shown during fasting for three days noted an improved immune response of chemotherapy patients when completing treatments in a fasted state!

The cancer patients studied were able to reduce the typical risk of infection and mitigate the development of other comorbidities when fasting during therapy.

A Quick Fasting Primer

Fasting is a simple process, it's more about what you don't do, and by that, we, of course, mean eating. The premise of fasting is eliminating caloric intake via foods or beverages within a decided time window.

While we strongly encourage stocking up on your favorite zero-calorie beverages, like coffee or tea—and, of course, water—to prepare for a fasted period there are additional tips to consider to maintain optimal health while fasting:

  • Select a fasting window that's realistic for your lifestyle and desired outcomes and be consistent. As we noted, fasting for varying durations provides different benefits, and the style you choose may center around your current physical health, lifestyle demands, and end goals.

    Whether you prefer a 16:8 window of fasting and feasting and only consume food within an eight-hour window, or turn your plate down over an entire weekend to maximize autophagy, select an approach and stick to it for a while to develop a rhythm and measure results.

  • Nix the Calories. Unlike creating a caloric deficit to encourage weight loss, a fast requires a virtually zero intake of calories not to impact your insulin or glucose levels or signal a need for the body to execute the energy-intensive digestion process.
  • The desire to eat is mostly a symptom of cravings and the body's expectation of a constant supply of calories. But, as we mentioned, hunger pangs tend to subside in the early stages of fasting, and folks find the process much more painless the longer they journey into their dietary pause.

    An authentic fast (a.k.a., water fast) includes no calories during the period of the process. However, as we noted, zero-calorie beverages like water, coffee, tea, and mineral-rich bone broth are permissible.

    Again, listen to your body and add in some form of calories—even in the form of a serving of energy-rich MCT oil—if you feel faint or otherwise unwell.

    However, if you're feeling great while fasting, omit caloric intake as a standard practice as anything with calories will break your fast.

  • Focus on Hydration. Sip on plenty of water during your fast and make it a point to get your electrolytes by adding ingredients like mineral-rich sea salt to the water, drinking grass-fed bone broth, or taking an electrolyte supplement.

    Fasting is a centuries-old powerful practice used in therapeutic, dietary, religious, and spiritual settings. And the benefits of stepping away from food for set periods can supercharge your body's functioning as well as its ability to recover rapidly or protect the immune system from pesky pathogens.

Plus, you may want to take a more in-depth look at our recent post for more details about different approaches to fasting, the most commonly used feeding schedules, and how to pair fasting with a low-carb, high-fat keto diet to maximize weight loss and improve overall health.

Fasting and the Keto Diet

As we've hinted, combining the potent powers of fasting and the ketogenic diet is undeniable. Either element provides a dynamic effect mirrored by the other and magnified when paired.

However, there are still some items to consider when fasting on a ketogenic diet to avoid common pitfalls and optimize your low-carb experience.

There are particular points to ponder if you are a woman and fasting. Also, food-inclusive varieties of dietary fasts associated with the keto diet, like the Beef and Butter Fast or the equally trendy Egg Fast offer nuance to the fasting paradigm that provides some benefits of fasting with less restriction.

Besides, intermittent fasting is a powerful daily practice for many on a ketogenic diet to encourage the body to rest, repair, and recover more rapidly and efficiently. And the cost of entry in terms of willpower is minimal.

And fasting can help you enter ketosis more quickly or return rapidly after a misstep—a fantastic tool to regain control after a random dietary splurge. Plus, you can further set yourself up for success with fasting by beginning the keto diet first, as entering ketosis or establishing some level of fat-adaptation—where your body recalls how to burn fat for fuel efficiently—aids in executing fasts with greater ease.

Breaking the Fast Consciously

Ending a fast requires some considerations, as does the start of a scheduled feeding protocol. Your body has been resting and repairing, and the meal we choose to reintroduce food to the mix is essential—likely the root of the adage that hails ‘break-fast’ as the most important meal of the day.

It's best to start slowly, maybe even with a soup or smoothie, something gentler for the body to assimilate and digest to replenish the body of needed vitamins and minerals.

Select something on the lighter side that's rich in healthy fat and moderate levels of protein, like the following:

  • Fermented foods and beverages like yogurt or milk kefir are a fantastic choice to consume when easing out of a fasting window. These foods provide nutrients and prebiotics to prime the gut and set the stage to digest food well.
  • Consider eating a simple meal like a scrambled egg with a hefty helping of sliced avocado for a fat-fueled option that's easy for the body to process and use for a boost of premium fuel.
  • A warm and cozy soup you can blitz together in moments is the perfect solution to ease back into eating solid foods following a fast—it’s satisfying yet easy on the body’s digestive system.
  • Add some roasted veggies to a savory and salted bone broth as a phase-in option to solids, providing a dose of needed electrolytes and hydration along with a welcomed reintroduction of texture after a stint of consuming strictly liquids.
  • A savory and slightly sweet soup, including pumpkin, feels like the perfect fast-breaker and a comforting culinary selection for fall.

The Takeaway

Fasting is a great practice to employ for many reasons, especially on a ketogenic diet. With this time-tested approach to controlled feeding, who wouldn't want to give it a try—to further support their weight loss efforts and boost overall vitality by simply eating (or not) more mindfully?

Whether you opt to try a fat fast to jumpstart weight loss or you're interested in water fasting to improve medical challenges or conditions, eating in controlled measures is an excellent way to encourage improved health while helping you lose unwanted weight effortlessly.

Plus, thanks to the natural appetite suppression so often experienced in metabolic ketosis and when fasting, turning down food and certain beverages become easy, especially when compared to the abundance of benefits found with this ancient process that remains as relevant as ever in modern times.


  • Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. (1992). The Journal of Clinical Endocrinology & Metabolism.
  • Gacche, R. N. (2021). Cancer and fasting: Can fasting/calorie restriction (CR) or fasting-mimicking diet (FMD) help fight cancer? Molecular basis of the fasting response. Dietary Research and Cancer, 159–169.
  • Fanti, M., Mishra, A., Longo, V. D., & Brandhorst, S. (2021). Time-restricted eating, intermittent fasting, and fasting-mimicking diets in weight loss. Current Obesity Reports, 10(2), 70–80.

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