September 28, 2022

Prolonged Fasting Benefits

You might have heard of intermittent fasting, or even tried it. Most people start with protocols such as 16:8, 5:2, alternate day fasting, or the one meal a day plan (OMAD). Intermittent fasting has many proven benefits, which include weight loss, improved cellular repair, greater mental clarity, and the upregulation of testosterone and growth

hormone. So, do these health benefits increase if you fast for longer? We take a closer look at the benefits of prolonged fasting to see what really happens when you go for 36 hours or more without food.

Intermittent vs Prolonged Fasting

Intermittent vs Prolonged Fasting

To fast is to abstain from food. Many are introduced to the concept of fasting for either religious or health reasons. In either case, intermittent fasting is the most common method. With intermittent fasting, you alternate between periods of fasting and periods of eating. Typically, fasting periods last no more than 24 hours.

Prolonged fasting, on the other hand, is commonly defined as abstaining from food for 24 hours or more. Popular long-term fasting protocols include the 48-hour or 72-hour fast. Some people choose to fast for up to 21 days. Man studies demonstrate that prolonged fasts are indeed safe.1 But are they more beneficial? We explore.

The Benefits of Long Term Fasting

The Benefits of Long Term Fasting

Studies that directly compare intermittent to prolonged fasting are difficult to come by, but we do have information on the benefits of longer fasts. What’s more, we know that most people won’t experience any benefit from fasting until they’ve abstained from food for 18 hours or more. We take a look at the details below.

Ketosis for Fat Loss

Perhaps the number one reason most people turn to fasting is to burn fat and lose weight. When the body is consistently being fed by sugars, it uses this sugar for energy. Deprive the body of carbs, and it will have to look somewhere else for fuel.

When the body switches from sugar to fat burning, this is called ketosis. Burning fat for fuel stabilizes blood sugar and reduces insulin resistance2 3 and can even improve exercise performance.4

Ketosis is fasting’s most sought-after benefit. But for most people, it won’t occur until at least 22 hours into your fast. So, break your fast at 24 hours and you’ve only spent a short time in ketosis. To maximize this benefit and continue to burn fat, you’ll want to fast for longer.


Autophagy is the turnover of dysfunctional or redundant cells, which makes space for newer, healthier cells. This process is vital for clearing waste from the body and improving the efficient delivery of nutrients. Autophagy may be a key component of gene stabilization as well as cancer, Parkinson’s and Alzheimer’s prevention.

When you hear stories of how fasting has improved people’s mental clarity, it’s largely due to an increase in autophagy, which reduces oxidative stress and inflammation.5

Autophagy occurs naturally in healthy people, but kicks into high gear after 24 hours of fasting and peaks after 48 hours.6 Periodically fasting for 48 hours or more can maximize the benefits of autophagy.

Human Growth Hormone

Autophagy keeps cells young by promoting cell turnover. Human growth hormone (hGH) is another factor researchers point to as a potential fountain of youth. hGH helps us preserve muscle mass, burn fat and repair soft tissue.

If you’re fasting to lose weight, the upregulation of hGH is just one reason why you’re more likely to preserve muscle, despite caloric restriction.7

When we’re in a fed state, studies indicate that hGH levels are unpredictable and will naturally decline with age.8 But fast for a minimum of 48 hours, and hGH production increases by an astounding 500%.9

Insulin Sensitivity

Insulin resistance not only increases the risk of obesity and type 2 diabetes, but leaves you feeling lethargic, thirsty and hungry. Blood pressure and triglyceride levels increase, as does the risk for major depressive disorder.10

While intermittent fasting can help reduce blood sugar in the bloodstream, prolonged fasts may have a greater impact on improving insulin sensitivity. When researchers compared the effects of a 12 versus 36-hour fast they found that fasting for longer was associated with an improved insulin-response during refeeding. This was true even though less insulin was secreted during the fast itself.11

Improved Immunity

As COVID-19 becomes endemic and novel human viruses continue to evolve, people are understandably interested in improving their natural immunity. In addition, a compromised immune system is at the center of a range of diseases.

Intermittent fasting helps reduce systemic inflammation, which takes pressure off an overworked immune system. But prolonged fasting may offer more specific immunity-boosting benefits.

Research on fasts between 48 and 120 hours have found the metabolic switch to ketone bodies improves resilience to stress and toxins. It also plays a critical role in regulating hematopoietic stem cells. These give rise to all other blood cells, including the white blood cells that protect us against infection.12

Basic Guide to Long-Term Fasting

Basic Guide to Long-Term Fasting

If you’re interested in long-term fasting, it’s recommended you first have at least some experience with intermittent fasting. It can be quite difficult to abstain from food for 48 hours or more if you’ve barely ever skipped a meal.

If your fast is 72 hours (3 days) or less, it’s safe to repeat the protocol monthly. A 72 hour fast benefits the mind and body considerably. If you’re fasting for 5-21 days, you might consider fasting seasonally or once per year. 13

To get the most out of your prolonged fast, consider the following tips…

Limit Carbs Before Fasting: Whether or not you’re planning a long-term fast, it’s beneficial to limit the carbohydrates in your diet.14 Immediately before fasting, a high carb meal is especially detrimental. So no, don’t load up on cake, potatoes and pasta because you’re about to go without. Not only will this leave you tired and hungry, but it will take you much longer to deplete stored sugars and enter into ketosis.

Hydrate While Fasting: Prolonged fasts are typically referred to as water fasts, because that’s what you’ll be focusing on in terms of consumption. Currently, nearly 40% of your hydration might come from food.15 To replace this when you’re not eating, you’ll have to drink more water than you normally do. If fasting for longer than 36 hours, a small pinch of salt in your water can help maintain electrolytes, especially if the water you drink has been filtered via reverse osmosis.

What About Dry Fasting? With dry fasting, both food and water are restricted. People typically abstain from water for up to 12 hours at a time, following this protocol for up to 6 days. Because dry fasting puts you at risk of dehydration, it’s best to dry fast alongside an intermittent fasting protocol.

Consider Your Workouts: There’s no reason not to exercise while fasting. At first, some minor protein loss will occur, but as ketosis takes over, protein levels will stabilize. Remember, the utilization of fat for energy may even improve your performance. A study of those mildly exercising while on a 10-day fast found that during the fast, non-weight-bearing muscles maintained their strength while weight bearing muscles got stronger.16

Because X3 strength training takes less than 20 minute per day to complete, there’s little reason to put it aside while fasting.

Understand How to Break Your Fast: Few people understand what to eat after a 48 hour fast. This is not the time to indulge in the carbs you’ve been missing. Not only will this cause a crash, but it does little to sustain the benefits you’ve worked so hard to earn.

Those who consume a full meal after an overnight fast continue to process sugars prior to fat. Thus, even if ketosis was reached, the body quickly shifts out of it.17 Consume a full, carb-heavy meal after a prolonged fast, and the body may fail to prioritize sugar processing. This can leave you in a hyperglycemic state, with excess blood sugar circulating in your bloodstream.18

To break 72 hour fast and avoid post-fasting hyperglycemia, refrain from refeeding with carbohydrates. This includes plant-based foods19. Instead, break your fast with a small high-protein snack such as beef jerky, hard boiled eggs, turkey roll-ups, or tuna.

And yes, start with a small snack. Introducing large amounts of food at once can lead to bloating, nausea or diarrhea.

Approximately 1-2 hours later, enjoy a high protein meal with plenty of healthy fats. Think steak topped with grass-fed butter or ground beef with slices of avocado. Eat slowly and continue to limit your per-meal calorie intake for 1-2 days.

Being smart about how you break your fast will help your benefits last longer and prevent you from experiencing any downsides of prolonged fasting.

With X3, you train with greater force to trigger Greater Gains


  1. Safety, health improvement and well-being during a 4 to 21-day fasting period in an observational study including 1422 subjects ↩︎

  2. Therapeutic use of intermittent fasting for people with type 2 diabetes as an alternative to insulin ↩︎

  3. Ketosis and appetite-mediating nutrients and hormones after weight loss ↩︎

  4. Acute nutritional ketosis: implications for exercise performance and metabolism ↩︎

  5. Practicality of intermittent fasting in humans and its effect on oxidative stress and genes related to aging and metabolism ↩︎

  6. Short-term fasting induces profound neuronal autophagy ↩︎

  7. Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss? ↩︎

  8. Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man ↩︎

  9. Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men ↩︎

  10. Incident Major Depressive Disorder Predicted by Three Measures of Insulin Resistance: A Dutch Cohort Study ↩︎

  11. Impact of prolonged fasting on insulin secretion, insulin action, and hepatic versus whole body insulin secretion disposition indices in healthy young males ↩︎

  12. Prolonged Fasting reduces IGF-1/PKA to promote hematopoietic stem cell-based regeneration and reverse immunosuppression ↩︎

  13. Unravelling the health effects of fasting: a long road from obesity treatment to healthy life span increase and improved cognition ↩︎

  14. Low Carbohydrate Diet ↩︎

  15. Contribution of Water from Food and Fluids to Total Water Intake: Analysis of a French and UK Population Surveys ↩︎

  16. Is muscle and protein loss relevant in long-term fasting in healthy men? A prospective trial on physiological adaptations ↩︎

  17. Effects of dietary fat on postprandial substrate oxidation and on carbohydrate and fat balances ↩︎

  18. Mechanisms of Whole-Body Glycogen Deposition after Oral Glucose in Normal Subjects. Influence of the Nutritional Status ↩︎

  19. The Effects of Prolonged Water-Only Fasting and Refeeding on Markers of Cardiometabolic Ris ↩︎

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