The 6 Stages of Fasting
Dr. Eric Berg
09/06/2024
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
How Does Intermittent Fasting Work?
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Easy Keto and Intermittent Fasting
Fasting is a powerful practice that triggers profound metabolic and hormonal changes linked to weight loss, steady blood glucose levels, and better cognitive functions.
Different stages of fasting offer unique benefits, ranging from initial depletion of glycogen stores and fat burning to deep ketosis, advanced autophagy, and immune cell rejuvenation.
Understanding the benefits of each fasting stage can help maximize the full potential of fasting to improve your health and longevity.
Fasting basics
Fasting refers to voluntarily abstaining from all foods and calorie-containing beverages for a set period.
Extended caloric restriction triggers various physiological, metabolic, and hormonal changes linked to improved metabolic health, enhanced cognition, and increased longevity.
These changes also support weight management, help reduce inflammation, and promote cellular repair, all of which contribute to better overall health and well-being.
While some individuals practice dry fasting, meaning they abstain from all food and liquids, water fasting is generally recommended as it permits fluid intake, which minimizes the risk of dehydration and associated health issues.
Fasting vs. starving
Fasting and starving are often confused. However, these distinct metabolic states trigger unique physiological processes with significantly different impacts on the body.
Starvation refers to an involuntary and prolonged lack of food, leading to severe energy deficits and malnutrition. This forces the body to break down fat and muscle tissue to release fatty acids and amino acids for energy.
This can cause substantial loss of lean muscle mass, severe body deterioration, and, in extreme cases, may result in organ failure, coma, or even death.
In contrast, fasting is a controlled and deliberate practice that shifts the body from using sugar and carbohydrates as fuel sources to burning fat to generate energy.
Fasting offers significant metabolic benefits, including enhanced insulin sensitivity, while generally preserving muscle mass and avoiding the severe health risks associated with starvation.
Types of fasting
Fasting has been practiced for centuries, and numerous methods and protocols have developed over time, each offering distinct approaches to restricting caloric intake.
Some of the most popular types of fasts include:
Intermittent fasting, also known as time-restricted eating (TRE), involves periods of fasting followed by a time-restricted eating window. The 18:6 method, a popular form of intermittent fasting, focuses on fasting for 18 hours each day and limits eating to six hours.
One meal a day (OMAD) is a fasting approach based on the principle that one large meal is consumed within a 24-hour period, with the remaining 23 hours dedicated to fasting.
Alternate-day fasting (ADF) consists of alternating between days of regular eating and days with a reduced caloric intake, typically between 500 and 600 calories.
Prolonged fasting includes caloric restriction for 1 to 5 days, followed by a return to regular eating patterns. Examples include 24-hour, 48-hour, 60-hour, and 72-hour fasts.
Watch the video below to learn more about the six stages of fasting.
6 Stages of Fasting
The 6 stages of fasting
Caloric restriction offers impressive benefits when practiced correctly, as each fasting stage induces a specific set of physiological changes that can contribute to significant health improvements.
Here are the six distinct stages of fasting.
8–14 hours
During the initial stage of fasting, your body relies on available blood sugar and begins depleting glycogen stores, which are reserves of glucose stored in the liver and muscle cells.
After around 10 hours of fasting, blood sugar and glycogen levels are declining, which inhibits the release of insulin, a critical metabolic hormone involved in blood sugar regulation and fat storage.
“When insulin levels drop, the body starts to initiate fat-burning by releasing fatty acids from fat cells,” explains Dr. Berg. “This shift moves the body from relying on sugars and carbohydrates as fuel to using stored body fat as its primary energy source.”
14–24 hours
As fasting progresses beyond 14 hours, the liver starts converting stored fat into ketone bodies, a group of organic acids that serve as a highly efficient fuel source when glucose is limited.
Research published in Nutrients found that ketones have neuroprotective properties linked to enhanced cognitive function, including mental clarity, memory recall, and problem-solving.
This likely explains why many individuals report heightened focus and concentration, reduced anxiety, and better moods during extended fasting periods.
Due to their appetite-suppressing effects, ketones not only support brain function but also help reduce hunger and cravings, making it easier to continue fasting.
At around 16 to 20 hours of fasting, the body triggers autophagy, a cellular repair process that removes and recycles damaged cellular components. This promotes overall cellular health and contributes to longevity by rejuvenating the body at the molecular level.
24–36 hours
Between 24 and 36 hours of fasting, the liver starts to burn fat more effectively. This leads to a surge in ketone levels in the bloodstream, signaling the onset of ketosis.
During this phase, fat burning intensifies as the body relies primarily on fat stores for energy, which explains why fasting for 24 hours and longer is associated with a significantly increased capacity to lose weight.
In addition, evidence published in Applied Physiology Nutrition and Metabolism found that fasting for 48 hours increased the concentration of brain-derived neurotrophic factor (BDNF) by 250 percent.
BDNF is a critical protein that plays a crucial role in supporting brain health by promoting the growth, maintenance, and survival of neurons.
Furthermore, BDNF helps stimulate the regeneration of brain cells and has been linked to a reduced risk of neurodegenerative disorders such as Alzheimer's and Parkinson’s disease.
36–48 hours
As fasting extends into the 36 to 48-hour range, advanced autophagy takes place. This not only aids in cell regeneration but also provides essential amino acids needed for physiological processes, minimizing the need to break down muscle tissue for protein synthesis.
Research published in the International Journal of Molecular Science summarizes the protein-sparing effects of autophagy as follows, “During nutrient deprivation, autophagy is enhanced to maintain a provision of important proteins and other nutrients to serve as an energy supply, thereby increasing cell survival.”
Additionally, when the liver isn’t occupied with processing nutrients, it can more efficiently clear and eliminate toxins, environmental pollutants, and metabolic by-products.
This enhanced detoxification capacity is associated with better liver function and helps lower oxidative stress and inflammation, which is linked to a reduced risk of cancer, cardiovascular disease, liver problems, and metabolic disorders.
48–60 hours
Fasting for more than 48 hours often induces a heightened sense of energy and mental sharpness and may be especially beneficial for those seeking to improve and optimize their metabolic health.
As insulin remains low due to a lack of dietary carbohydrate intake during extended fasting, cellular insulin sensitivity improves. This enhances cellular responsiveness to insulin signaling, which supports optimal blood sugar control and may help prevent and reverse insulin resistance.
Poor blood sugar control and insulin resistance are the main drivers of serious health issues, including obesity, metabolic syndrome, diabetes, and heart disease.
Fasting exposes the body to physiological stress, which triggers survival mechanisms such as autophagy and growth hormone release.
Increased growth hormone production helps mobilize fat stores for energy production, maintains muscle mass, and supports the regeneration of cells and tissues.
60–72 hours
Approaching the 72-hour mark of a prolonged fast can trigger a mix of physical and mental fatigue but also a profound sense of accomplishment and rejuvenation.
In addition to accelerated fat burning, the body undergoes remarkable changes in immune system function during the final stages of an extended fast lasting up to 72 hours.
A study published in Cell Stem Cell found that a 72-hour fast can help clear out old, damaged, and dysfunctional immune cells and stimulate the production of new immune stem cells, enhancing the body's ability to fight infections and recover from illness.
The authors propose that prolonged fasts could be particularly beneficial for individuals undergoing chemotherapy, as this may reduce treatment-related cellular damage and enhance recovery by supporting the renewal of critical immune defenses.
The body’s ability to renew immune cells, stimulate cellular repair mechanisms, and promote healing is one of the most profound benefits of extended fasting.
How to start fasting
While longer fasts yield the most health advantages, achieving prolonged periods of fasting can be challenging, especially for beginners.
If you are new to fasting, it’s recommended to begin with an intermittent fasting routine to help your body adapt to abstaining from food for extended periods.
As your body becomes accustomed to fasting, you can progress to longer fasts, such as 24 or 48 hours, to fully experience the benefits of caloric restriction. To enter the fifth and sixth stages of fasting, gradually work up to a 60-hour or 72-hour fast.
However, it’s crucial to prioritize hydration and electrolyte replacement and consider fasting-friendly supplements to support your body's nutritional needs during prolonged fasting routines.
Before starting an extended fast, it's essential to eat nutritious high-fat meals rich in nutrients and healthy fats to stay satiated and energized.
This explains why combining fasting with a nutritious ketogenic diet such as Healthy Keto® is an excellent strategy to achieve longer fasting periods while keeping your body in fat-burning mode during your eating windows.
It’s equally important to carefully plan how to break a fast, especially fasting periods that last longer than 24 hours.
It’s generally best to end a longer fast with small amounts of easy-to-digest foods, such as soups or bone broth, and gradually introduce solid foods over several hours. Eating heavy meals after fasting can overwhelm your digestive system and cause diarrhea, bloating, and abdominal pain.
Who shouldn’t fast?
While extended fasting has impressive health benefits, it isn’t recommended for breastfeeding mothers, pregnant women, or individuals trying to gain weight.
In addition, fasting triggers significant hormonal changes and can lead to electrolyte imbalances if essential minerals aren’t replenished, which can cause various adverse health effects.
Therefore, it’s crucial to discuss prolonged fasting with a healthcare provider if you are taking prescription medication or have underlying health conditions such as low blood pressure, type 1 diabetes, or cardiovascular disease.
Fasting also isn’t suitable for individuals with a history of eating disorders as it can trigger unhealthy behaviors or exacerbate existing patterns of disordered eating.
Key takeaways
Prolonged caloric restriction triggers a series of beneficial physiological changes that occur in sequential order, beginning with glycogen depletion and initiation of fat-burning, followed by deep ketosis and cellular renewal.
Fasting for more than 36 hours progresses into accelerated fat loss, advanced autophagy, restoration of insulin sensitivity, and immune system regeneration.
These stages of fasting collectively enhance fat burning, improve cellular health through autophagy, strengthen immune function by regenerating immune cells, and promote metabolic health by increasing insulin sensitivity and optimizing energy utilization.
FAQ
1. What are the 6 stages of fasting?
Glycogen depletion, initiation of fat burning, and ketosis are the first stages of fasting. As caloric restriction continues past the 36-hour mark, the body enters advanced autophagy, enhances insulin sensitivity, and undergoes significant immune cell renewal at around 60 to 72 hours of fasting.
2. What is the hardest stage of fasting?
The hardest stage of fasting is usually the transition into ketosis, which typically occurs after around 24 hours of caloric restriction. During this period, individuals may experience irritability, cravings, and hunger.
However, once the body fully adapts to fat burning, most people notice improved mood, enhanced mental clarity, and reduced cravings.
3. What stage of fasting burns the most fat?
Once the body enters ketosis at around the 24-hour mark, the body starts to rely on stored body fat to generate energy until the fast is broken.
4. What are the benefits of fasting for 72 hours?
Fasting for 72 hours offers significant health benefits as it stimulates the regeneration of immune stem cells, which can rejuvenate the immune system and improve overall resilience.
In addition, fasting for up to three days promotes advanced autophagy, a crucial cellular repair mechanism that clears damaged and dysfunctional cellular components, linked to enhanced cellular health and longevity.
Sources
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