Intermittent fasting and time-restricted eating have become quite popular, and now people are taking notice of longer fasts — especially 36 hour ones. While the human body can survive a short period without food, a longer fast causes your body to undergo many metabolic and hormonal changes that can alter your energy level, brain function, and overall health.
First 6-12 hours: Stored Fuel To Start
After the last meal, your body’s initial fuel source will be the glucose from recently consumed food. To help cells absorb sugar into the bloodstream to produce energy, your body has increased levels of insulin. Once food is completely digested, insulin levels decrease and your body will begin using glycogen, the stored glucose (which is primarily stored in the liver), as a source of energy.
During this time, you will not have developed enough of an empty stomach to cause any significant feelings of hunger.
12-24 hour period: Glycogen Stores Are Depleted
At the end of the 12-24 hour period, you have completely used your liver glycogen stores and are no longer consuming calories. As your body has run out of glycogen stores, it is now forced to break down fat for energy.
At this point, your liver begins producing ketones from fat to serve as an alternate source of energy. In addition to creating ketones, your body will release additional hormones that cause increased feelings of hunger. Many people describe this stage as irritability, headaches, fatigue, or trouble concentrating; which has been referred to as the fasting flu.
24–36 Hours: Fat Burning and Ketosis Increase
During the first 24-36 hours of fasting, the body enters a state of deeper ketosis, where it relies more on fat and ketones as its main fuel source for both the brain and the muscles. Insulin levels are also lower than during times of feeding, which may lead to improved insulin sensitivity in some individuals.
In addition to entering a state of deeper ketosis, the body also produces more growth hormone, which helps maintain muscle mass and promote repair of tissues. If there isn’t appropriate hydration and electrolytes, individuals may experience dizziness, weakness, and low blood pressure.
Protein Obsession May Be Linked to Inflammation and Blood Sugar Spikes
Autophagy: Cleaning Up Cell Damage
Autophagy is one of the major topics of discussion when discussing longer-term fasting. During autophagy, cells begin to degrade and recycle damaged components. Studies have shown that autophagy appears to increase with prolonged fasting, possibly helping to support cellular health and longevity.
Most of the studies that are available report autophagy in animals only, and researchers are currently looking for evidence to show how long of a fast humans need to create a significant activation of this process.
Brain Health and Mood
Some individuals report mental clarity and improved focus during a 36-hour fast. This may be due to a steady supply of ketones to the brain during this period. In contrast, some individuals report feeling brain fog, anxious, or having a low mood.
Individual responses to fasting depend on several factors including prior diet, level of stress, amount of sleep, and metabolic fitness.
Waking Up Between 3 AM and 5 AM Could Signal Underlying Health Issues
Risks and Who Should Avoid It?
Some potential dangers of extended fasting (especially if repeated or done incorrectly) include dehydration, imbalances in electrolytes, low blood sugar and loss of muscle mass.
The Truth of the Matter
The 36 hr fast transition your body’s metabolism from burning carbohydrates to fats and may initiate the cellular repair process. While some individuals have a positive response to fasting, others can experience severe adverse effects from fasting for extended periods. Health and wellness professionals agree that when considering longer fasts, you should have appropriate medical supervision and approach fasting very cautiously, and, for most people, the health benefits of fasting can be achieved without fasting for 36 hours or longer.
Remember, any significant dietary modification will vary for each individual and follow the proper medical advice.
What Your Legs and Feet Can Reveal About Hidden Health Issues
