The 36-hour fast, sometimes called the “Monk Fast,” is an advanced form of intermittent fasting involving abstaining from all caloric intake for a continuous day and a half. This practice typically means finishing dinner one evening, skipping all meals the following day, and not eating again until breakfast the day after. The 36-hour duration is long enough to prompt significant physiological shifts in the body. This extended fast forces a deeper metabolic transition, requiring an understanding of the changes that occur inside the body over this period.
Metabolic State During a 36-Hour Fast
The body initially relies on glucose from the last meal, but this supply is consumed rapidly. The body then mobilizes stored carbohydrates known as glycogen, primarily located in the liver. This glycogen reserve is depleted between 12 and 24 hours of fasting, signaling the end of the fed-state metabolism.
After glycogen stores are exhausted, the body switches its fuel source to stored fat, initiating lipolysis. Fat molecules are broken down into fatty acids, which the liver converts into ketone bodies. Ketone production increases toward the 36-hour mark, leading to nutritional ketosis. Ketones become the main energy source for the brain and muscles.
The 36-hour duration significantly ramps up cellular autophagy, a process of cellular clean-up and repair. Autophagy intensity increases notably once the body is fully committed to the fasted state. Damaged components and dysfunctional proteins are recycled, contributing to cellular renewal. This extended period also corresponds with a surge in human growth hormone (HGH), which helps preserve lean muscle mass while promoting fat metabolism.
Documented Effects on Health Markers
The metabolic changes induced by the 36-hour fast translate into measurable effects on various health markers. A primary outcome is the improvement in insulin sensitivity and glucose regulation. Prolonged fasting lowers both fasting plasma glucose and insulin levels, benefiting metabolic health. Although some studies show a temporary decrease in insulin sensitivity during the fast, the long-term effect of regular fasting protocols is a reduction in insulin resistance.
The shift to fat oxidation also benefits cardiovascular health. Intermittent fasting protocols, including the 36-hour fast, help lower blood pressure, total cholesterol, and triglyceride levels. These changes indicate a reduced risk profile for chronic diseases associated with metabolic dysfunction.
When utilized regularly, the 36-hour fast contributes to weight management through a significant caloric deficit. While initial weight loss includes water weight from glycogen depletion, the sustained fat-burning state aids in reducing body fat and waist circumference. Furthermore, activated autophagy and reduced systemic inflammation are linked to improved cellular resilience and may protect against age-related decline.
Safety Considerations and Exclusion Criteria
Although the 36-hour fast offers benefits, it is not suitable for everyone and requires careful consideration. Individuals with Type 1 or Type 2 diabetes, especially those taking insulin, face an elevated risk of hypoglycemia or other metabolic complications and should only attempt this under medical supervision. Pregnant or breastfeeding women must also avoid prolonged fasts due to increased nutritional demands.
People who are underweight, have a low body mass index (BMI), or have a history of eating disorders should not engage in this type of fasting. Temporary side effects are common and may include headaches, dizziness, fatigue, and irritability. If these symptoms become severe or persistent, the fast should be discontinued immediately.
Proper hydration is necessary during the entire 36-hour period, as the body can lose water and electrolytes. Consuming non-caloric fluids, such as water, black coffee, or herbal tea, prevents dehydration. Supplementing with electrolyte-rich water helps maintain the balance of essential minerals like sodium and potassium, minimizing the risk of weakness or imbalance.
Ending the Fast Properly
The re-feeding phase immediately following the 36-hour fast is a sensitive time for the digestive system. The digestive tract has been resting, and a sudden influx of a large, heavy meal can cause discomfort, including bloating and nausea. The goal is to gently reintroduce food to avoid overwhelming the gut and prevent a rapid spike in blood sugar and insulin levels.
The initial meal should be small, easily digestible, and nutrient-dense. Recommended first foods include bone broth, which aids hydration and provides minerals, or small amounts of fermented foods like sauerkraut to support gut health. Soft-cooked vegetables and easily digestible protein sources, such as eggs or fish, are also good starting choices.
Foods to avoid immediately include:
- Large portions of any kind.
- High-carbohydrate or sugary items.
- Processed foods, as these can negate the metabolic benefits.
- High-fat or very dense protein meals, such as red meat, which are difficult to process due to reduced enzyme production.
Gradual reintroduction over several hours ensures a smooth transition back to a normal eating pattern.