January 16, 2015 in Exercise, Health, Nutrition

Benefits of Fasting

Healthful, home-cooked food
Good food is the cornerstone of good health

[NOTE: This article has not quite aged gracefully as modern nutritional sciences understand the metabolic pathways far better than they did at the time of writing. For updated information, be sure to read my comment below to get a better understanding of how things work.]

Long-time readers of the Living Intentionally blog know that I am a big fan of fasting. Regular fasting beautifully complements a healthful diet that is rich in healthful fats, adequate in protein and low in non-vegetable carbohydrates and grains.

I think fasting is an essential aspect in realizing and maintaining excellent health. It doesn’t need to be anything difficult, either. Generally speaking, intermittent fasting is enough to gain significant advantages. Whereas traditional fasting will have one forgoing food for 24 hours or more, intermittent fasting typically has one restricting food intake to a particular window of time every day. For me, for example, I typically only eat one or two meals between the hours of noon and 6 p.m. on any given day. The rest of the time, I limit my intake to fluids.

Longer, more traditional fasting has its place, too. Fasting for 48-to-96 hours has a dramatic effect with regard to the recycling of dead and damaged cells. During such prolonged fasting, damaged white blood cells are recycled to provide the body with necessary scavenged proteins. When the fasting has ended, the damaged immune system cells are replaced with healthy cells once again. The result is improved immune health and increased overall well-being.

Fasting is an important element in maintaining a fat-burning metabolism. Most people eat far too much with far too much regularity, which means that we never get our bodies into a state of even temporary starvation. Our biology is based on cycles of feast and famine. When we’re in a constant state of feast, the body’s maintenance schedules are interrupted, causing us to age prematurely.

Otherwise healthy people who experience low blood sugar when they don’t eat are experiencing symptoms of a metabolism that has been trained to derive its energy almost entirely from glucose. In essence, the body might know how to store excess energy as fat, but it has almost forgotten how to use fat as a source of energy. Intermittent fasting is a great way to train the body to derive its energy from fat stores.

During prolonged fasting, the body enters a state known as ketosis. When your body has become well accustomed to dealing with the feast/famine cycle, your brain shifts from primarily using glucose for energy and relying more on ketones. Ketones are an energy source derived from fat-based metabolism.

Your body’s muscles, including your heart, operate extremely well with ketones as a fuel source thanks to having an enzyme that enables them to convert ketones to glycogen. Your brain prefers glucose as a fuel because it is missing the enzyme that your muscles employ, but here your liver helps out. When your blood sugar drops and ketones become elevated, your brain signals to your liver to produce a ketone-like substance called beta-hydroxybutyrate. Your brain is able to use this compound as fuel quite efficiently with practice.

With practice is an important point here. The body absolutely thrives on the feast/famine cycle. Regular fasting promotes a number of processes within the body that stimulates protein reclamation, dead-/damaged cell recycling and helps to reduce inflammation.

Extreme fasting, e.g., longer than 3~4 days, should be avoided at all costs. Extreme fasting stresses the body beyond healthful norms and puts it squarely into the realm of survival mode. Beyond approximately 3 days of fasting, the body loses its ability to produce fuel for the brain. To compensate for the lack of brain food, which is essential for staying alive, the body breaks down its own muscle tissue to provide the necessary proteins for fuel synthesis. This has highly destructive side effects and should be avoided. I recommend, and personally practice, restricting fasting to a maximum of 3 days.

Fasting has numerous health benefits when done with care and not to extremes. The more regularly you limit your intake, the more you’ll find your hunger cravings diminishing. Regular fasters know well that our sense of hunger largely goes away as we have trained our body to derive its energy primarily from fat-based metabolism.

Try it!


  1. March 21, 2018 at 8:23 am



    I would like to see the data on the dangers of fasting beyond 4 days. Based on my research this can be quite healthy and is completely dependent on your health circumstances.

    1. March 21, 2018 at 1:11 pm

      Trane Francks


      Hi, Sara!

      Thanks for dropping by and asking about this. You can do your own research on the subject by looking up the terms ‘fasting’ and ‘catabolism’. The classical view is that protein catabolism upregulation stays in effect even after the liver glycogen reserves are depleted. It is at this time that the classical understanding suggests that catabolism begins to break down muscle tissue to fuel the brain.

      Three years later and we’re beginning to see different views of the metabolic pathways that explain what happens in the body during longer fasts. Dr. Jason Fung, a Canadian nephrologist, has studied the biochemistry and determined that when we’re fasting, protein catabolism is actually downregulated and growth hormones are upregulated.

      With the depletion of liver glycogen, it seems that there are excess amino acids that need to be metabolized, i.e., burned. It is here that the classical view is “you’re burning muscle”, but Fung considers this to just be normal turnover. That turnover goes way down during fasting, however, and fat oxidation increases dramatically. Which now leads me to directly refer to your point:

      If we assume that Fung’s view of the metabolic pathways during fasting are correct, our healthy limit of fasting is more or less only determined by the amount of fat we have. There is a bottom line of healthy percentage of fat for a given weight, so it’s not as though we can fast for an infinite period before the bottom falls out. As well, healthy fasting assumes “within norms” values for all our essential vitamins, minerals and nutrients.

      So, if you’re a completely healthy person who is just looking to detox and gain the benefits of fasting, of which I think there are many, a few days here and there shouldn’t be an issue. I would advise females to not allow their body fat drop below about 12% and males should limit their minimum to ~8%. Few people outside of elite athletes have such low numbers.

      If one is suffering from dietary imbalances that have skewed their nutrient profile, intermittent fasting under the supervision of a qualified medical professional is likely preferred versus long-term fasting, with possibly one notable exception: I have long been looking at the use of fasting as a self-care approach in dealing with cancer. There seems to be a reasonable amount of supporting evidence that suggests that our cellular metabolism can effectively be ‘reset’ with a fast of ~10 days duration.

      Given that cancer is essentially a cellular metabolism disorder, it makes sense that extreme fasting would be effective here. Healthy cells are able to adapt to the environmental stress of fasting and change how they get their energy. Cancer cells lack that adaptability, and so extreme fasting could be an excellent component of one’s recovery strategy.

      I appreciate your point and I am in complete agreement with your research findings. I should probably update this article to reflect modern metabolic understanding.

      Warmest regards,

      1. September 27, 2020 at 4:31 am

        Leela Godavari


        Thank you 😊 so very much for this incredibly informative and helpful article!! I just completed my second “long fast “ (96 hr). I was curious what physical benefits I might be achieving.

        I found your article and am so encouraged by this data!! After eating horribly, and I mean horribly, most of my adult life, (lots of cola drinks, candy bars and chips), I am successfully fixing pre-diabetes and many hormonal issues thru fasting!

        I eat a mostly plant-based diet; but include raw goat-milk kefir, duck eggs and pastured beef (only once a month) from a local farm. I also walk 3 miles a day and rebound. Next goal is to incorporate weightlifting 🏋️‍♀️ !!

        I am so grateful to you and the many informative helpful people who write blogs like yours. I rely on these, and some videos on YouTube, to help me make informed choices.

        Thank you for your time and research. You are helping people like me to transform their bodies, minds, and lives for the better.

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