At a glance
A 36-hour fast is a prolonged fasting strategy that shifts the body into ketosis, promoting fat burning, improved insulin sensitivity, and cellular repair through autophagy. These metabolic changes may offer health benefits such as weight loss, enhanced cognitive function, and improved cardiovascular health. Understanding how to properly structure and maintain a 36-hour fast can help maximize results while minimizing potential risks.
Prolonged fasting triggers metabolic and cellular adaptations as the body shifts from glucose dependence to stored fat for energy production and homeostasis.
This extended fasting strategy influences key processes involved in weight regulation, insulin sensitivity, brain function, and cellular repair.
Discover 36-hour fasting benefits, how to get started, and practical tips for success.
What is a 36-hour fast?
A 36-hour fast is a type of prolonged fasting in which you abstain from food and calorie-dense beverages for 36 consecutive hours.
Compared to intermittent fasting schedules, such as the 16:8 pattern, which involves fasting for 16 hours each day followed by an eight-hour eating window, 36-hour fasts are typically practiced once a week, every two weeks, or less often.
Watch the video below to learn about the six stages of fasting.
How a 36-hour fast affects the body
During a 36-hour fast, the body gradually shifts from relying on glucose from food to using stored energy to support survival and essential biological processes.
In the first 8 to 14 hours, blood sugar levels begin to stabilize as the body depletes circulating glucose and glycogen stored in the liver and muscle tissues. As these reserves decline, insulin levels decrease and the body begins preparing to switch to using stored body fat for energy.
Between 14 and 24 hours, glycogen stores are depleted, and the liver begins converting stored fat into ketones, a metabolic state known as ketosis.
“Ketones serve as a highly efficient fuel source when plasma glucose declines,” explains Dr. Berg. “They readily cross the blood-brain barrier to support brain function and help preserve skeletal muscle while supplying energy to the heart.”
At this stage, the body also enters autophagy, a cellular repair process that helps break down and recycle damaged proteins and cellular organelles.
By 36 hours, the body is in a deeper state of ketosis and fat burning. Levels of the hunger-stimulating hormone ghrelin decrease, and feelings of hunger are reduced.
Potential benefits of a 36-hour fast
A 36-hour fast can activate several biological processes linked to metabolic health, neurological function, and cellular resilience.
Here are six potential health benefits of a 36-hour fast.
1. Accelerated weight loss
As the body enters a deeper state of ketosis, it relies on stored fat to fuel essential functions, which can directly support weight loss.
A study published in Cureus found that 36-hour fasting may help promote long-term reductions in body weight without increasing hunger or slowing metabolic rate.
2. Better glycemic control
Extended fasting causes blood glucose to decline due to the absence of food intake, which lowers circulating insulin levels.
This reduction in insulin allows the body to transition toward fat metabolism and may improve insulin sensitivity, enabling cells to use glucose more efficiently when it becomes available.
Over time, this can improve glycemic control and reduce the risk of insulin resistance, a metabolic imbalance associated with conditions such as type 2 diabetes, polycystic ovarian syndrome (PCOS), and non-alcoholic fatty liver disease (NAFLD).
3. Enhanced cognitive function
As the body enters ketosis, the brain uses ketones as an energy supply for neurons, which is often associated with cognitive benefits such as mental clarity and focus.
Fasting-induced autophagy also helps clear damaged proteins that can accumulate in brain tissue, which may help lower the risk of neurodegenerative diseases such as Alzheimer’s and other forms of dementia.
A study published in Inflammation Research found that “autophagy… contributes to a reduction in Aβ-plaque levels, as neurons degrade intracellular Aβ, and glial cells degrade extracellular Aβ through autophagy.”
4. Raised mood
Extended fasting influences key neurotransmitters involved in mood, including serotonin, dopamine, and gamma-aminobutyric acid (GABA), which regulate emotional stability, motivation, and stress response.
Fasting also increases levels of brain-derived neurotrophic factor (BDNF), a protein that supports neuronal health, plasticity, and resilience.
By reducing inflammation, improving metabolic balance, and enhancing stress resistance, fasting may elevate mood and boost the body’s ability to cope with stress.
5. May lower the risk of heart disease
Fasting may support cardiovascular health by improving low-density lipoprotein (LDL) cholesterol levels and reducing inflammation markers linked to atherosclerosis.
These effects help limit plaque buildup within arterial walls and support overall vascular function.
Research published in the European Journal of Nutrition found that fasting improves lipoprotein levels and shifts lipoprotein subclasses toward a less atherogenic profile, reducing the risk of heart disease associated with abnormal cholesterol and triglyceride levels.
6. Helps protect against cancer
Fasting-induced autophagy helps clear damaged cellular components, including dysfunctional mitochondria.
Because mitochondrial gene mutations are linked to abnormal cell growth and tumor development, their removal may help reduce cancer risk.
Additionally, reduced glucose availability during ketosis may create a less favorable environment for cancer cells, which often rely on glucose to support rapid growth and proliferation.
How to do a 36-hour fast
A 36-hour fast is often structured around mealtimes, beginning after your final meal of the day and continuing through the following day without food.
As an example, you may have your last meal at 6 p.m. and break your fast at 6 a.m. two days later.
Before beginning, it’s recommended to eat a nutrient-dense meal rich in healthy fats, moderate protein, and low-carbohydrate vegetables.
Keeping carbohydrates low before the fast helps stabilize blood sugar and insulin levels, allowing the body to transition into fat-burning mode more easily.
When fasting, staying hydrated with water and sugar-free electrolytes can help reduce fatigue and side effects such as headaches or dizziness.
Finally, when breaking a 36-hour fast, start slowly with small amounts of low-carbohydrate foods such as bone broth, a small leafy green salad, or a boiled egg, to avoid shocking the digestive system.
Slowly reintroducing food also reduces the risk of refeeding syndrome, a rare but potentially life-threatening condition caused by rapid shifts in fluid and electrolyte balance.
Tips for a successful 36-hour fast
Prolonged fasts are challenging but may be a logical next step for those looking to further improve energy efficiency, support cell repair, and enhance metabolic flexibility.
Here are six tips for fasting success.
1. Consume fasting-friendly drinks
Staying hydrated is essential when fasting for an extended period. Plain water with sugar-free electrolyte powder, lemon juice, or a pinch of sea salt can help support electrolyte balance.
Other fasting-friendly drinks include black coffee and herbal teas, such as green tea, which may enhance autophagy.
Bulletproof coffee prepared with grass-fed butter, whole cream, or medium-chain triglycerides (MCT) oil is another good choice for those who don’t enjoy black coffee.
Pure fats have minimal impact on insulin levels and can promote satiety and curb cravings without breaking your fast.
2. Support nutrition with supplements
Research published in the Current Opinion in Clinical Nutrition and Metabolic Care found that fasting can contribute to deficiencies, particularly in B vitamins, vitamin C, calcium, magnesium, potassium, and folate.
Taking supplements while fasting can reduce the risk of developing or worsening nutrient gaps without significantly impacting blood sugar or insulin levels.
Good options include a B vitamin complex from nutritional yeast, vitamin D from cod liver oil, wheatgrass juice powder, and trace minerals.
However, avoid collagen and protein supplements, including whey protein and branched-chain amino acids (BCAAs), which raise insulin levels and inhibit ketosis and autophagy.
3. Reduce physical activity
Even if your primary goal is weight or fat loss, it’s recommended to avoid intense workouts during a 36-hour fast.
Overexertion may lead to lightheadedness and fainting in some individuals, especially those who are new to fasting.
Instead, light activities such as walking outdoors or gentle stretching can help ease fatigue and redirect your attention away from food.
4. Keep your mind busy
During the initial hours of fasting, hunger often comes in waves, triggering cravings and the urge to eat.
Redirecting your attention to relaxing hobbies, light chores, reading, journaling, or other engaging activities can help distract you from hunger.
5. Prioritize quality sleep
Getting enough quality sleep can also make prolonged fasts easier.
Poor sleep can elevate cortisol—the primary stress hormone—and increase hunger hormones, such as ghrelin, while lowering leptin, the hormone that signals fullness.
This hormonal shift can intensify cravings as the body attempts to compensate for sleep deprivation.
6. Start slowly
If you’re new to fasting, start with shorter fasting periods and slowly increase the duration as you build tolerance. Gradually extending fasting windows toward 36 hours can help your body adapt and become more efficient at using stored body fat.
Safety considerations and who should avoid fasting
While generally safe for healthy adults, 36-hour fasts may not be appropriate for everyone.
Pregnant or breastfeeding women, children and adolescents, and those with a history of eating disorders should avoid extended fasts due to increased nutritional demands and potential health risks.
Prolonged fasting may also be unsuitable for those who are underweight, managing diabetes, taking certain medications, such as blood thinners, that require food for absorption.
It’s recommended to consult a healthcare provider before attempting a 36-hour fast or any fasting regimen, especially if you have an underlying health condition.
If you begin a prolonged fast and experience dizziness, weakness, confusion, heart palpitations, or fainting, break the fast with a small snack, such as a boiled egg or leafy green salad.
Seek medical attention if symptoms persist or worsen.
Key takeaways
- A 36-hour fast involves abstaining from food for 36 consecutive hours, which puts the body in a deep state of ketosis and autophagy.
- 36-hour fasting benefits may include sustained weight loss, improved glycemic control, recycling of damaged cells, enhanced cognitive function, boosted mood, and reduced disease risk.
- To do a 36-hour fast, eat a nutrient-dense meal before fasting, stay hydrated during the fast, and break the fast slowly with a small, low-carbohydrate meal.
- Drinking fasting-friendly beverages, taking supplements, reducing activity, prioritizing sleep, and engaging your mind can help ensure a successful fast by promoting satiety and reducing the risk of side effects.
- Consult your healthcare provider before attempting a prolonged fast, especially if you have underlying health conditions or take medications.
FAQ
- 1. Is a 36-hour fast better than intermittent fasting?
- 2. How often can you do a 36-hour fast?
- 3. What can you drink during a 36-hour fast?
- 4. Will a 36-hour fast slow your metabolism?
- 5. How do you break a 36-hour fast safely?
