The first article in the series, Ketosis and Fasting Part I: What Is Fasting and Why Do People Do It?, defines fasting and outlines some of the many purported benefits.  This next segment explores different protocols for intermittent (under 24 hours) fasting.

Meal Timing

While prolonged daily fasting (24+ hours) has a host of other hormonal and metabolic benefits, many people incorporate shorter fasts into their daily routine by restricting the frequency of meals.  Eating fewer meals per day can result in body fat loss, a decrease in cortisol levels, along with other interesting changes (Stote et al., 2007).  Reducing meal frequency—intermittent fasting (IF)—allows for the benefits of fasting without requiring the individual to abstain from food for too long.  One can both fast and feed within a 24-hour period, allowing for the best of both worlds.

There are a number of popular protocols for IF.

  1. 16/8 Intermittent Fasting may be the most popular introductory protocol for IF. The “16” and “8” suggest that a person does not eat for 16 hours and then consumes all meals within the remaining 8 hours of the day.  One way to do this easily is to skip breakfast.  If the first meal of the day begins at 12 pm and the last meal is completed by 8 pm, then the fed window is 8 hours and the fasting window extends from 8 pm to 12 pm the following day.  My personal variation is to eat each day between 12-2 pm and to finish my last meal by 6 pm most days (18/6 or 20/4 IF).  The benefit of this approach is that the time spent sleeping counts towards the window during which a person fasts.  Being asleep for 8 hours of a fast makes fasting much easier to do.
  2. The Warrior Diet (Hoffmekler, 2001) suggests that the faster allows 20 hours to pass between meals and then allows for a 4-hour eating window specifically in the evening. This specific protocol, published before other intermittent fasting protocols were popularized, suggests both an eating strategy and a lifestyle strategy.  Food is to be under eaten for 20 hours per day and then overeaten or feasted upon during a 4-hour window in which one primary meal is consumed.  The protocol goes on to explain how important a circadian rhythm is for helping to set the natural feast and famine timings during a 24-hour day.
  3. Alternate day fasting is based on research which shows that individuals who restrict their caloric intake or fast entirely for one day and eat in unrestricted quantities after fasting as long as they continue to alternate fast and fed days. Whether a person fasts for 24 hours on alternate days (Every Other Day Diet by Krista Varady), fasts for 24 hours once or twice per week (Eat, Stop, Eat by Brad Pilon) or completes two 23 hours fasts over the weekend with one meal per day (The Fast Diet by Michael Mosley), the results of mixing fasting days with fed days include loss of bodyfat and not muscle, reduced BMI, decreases in cholesterol, blood pressure heart rate and a stronger heart (Varady, 2009).
  4. Macronutrient restriction is a unique form of fasting. Rather than ceasing to take in any calories, it allows a person to eat one (or two) macronutrients while restricting just one (or two).  Confused?  Let’s look at the forms this may take.
    1. One example is a ketogenic diet. Ketogenic eating is a form of carbohydrate restriction, but it allows a person to still eat protein and fats.  This enables the body to produce ketone bodies and also enables chaperone mediated autophagy (see the previous post titled Ketosis and Fasting Part I for details).
    2. Protein restriction enables macro and microautophagy. Low carb authors and thought leaders such as Dave Asprey and Leanne Vogel advocate what is called “protein fasting” which encourages the body to recycle cellular junk matter and clean up malfunctioning cells in the body.  This can be induced by restricting carbs even if the person eats protein and fat.
    3. Restricting both protein and carbs simultaneously allows all three forms of autophagy to occur at once. Also known as fat fasting, a person can enjoy the benefits of all three forms of autophagy but without going calorie free and potentially hungry.  This is not necessary, however, to benefit from all three forms of autophagy.  The Whiton Protocol, developed by Josh Whiton, is one example of cycling between carbohydrate and protein restriction. He suggests eating a high fat, low-to-moderate protein and carb diet (70% fat, 15% carbs, 15% protein) five days per week to induce ketosis and CMA.  During the remaining two days, protein is limited to under 15 grams per day.  This protocol not only induces all types of autophagy over the course of a week, but it also leads to decreases in IGF and the mTOR pathway, both of which have been determined to be essential for decreasing aging and increasing longevity (see The Whiton Protocol for details).  In other words, there are several ways to do macronutrient restriction which can result in autophagy and other healing benefits.

Whether or not fasting is the right approach for you can only be determined by your personal response to fasting.  If you are eating a ketogenic diet and have experienced the side effect of hunger loss, then fasting may be a natural and easy approach to shedding body fat and improving your health.  Experiment with meal skipping, or with consuming fat only and avoiding carbs and protein for the same autophagic benefits, and see how you feel.  Fasting intermittently is a great way to reap the benefits of fasting while still having a full belly at the end of the day.

I must repeat my final comment from last week’s post because it is the most essential component for allowing a fasting to work effectively without causing harm.  Fasting is not for those who are new to ketosis, pregnant, breastfeeding or struggling with other stressors because it can make those stressors worse.  It is also very important that people eat the appropriate amount of food during the fed window so as to not combine meal timing restriction with calorie restriction.

If you limit when you eat and then eat a very limited number of calories when you finally do it, then your body is hit twice with a sense of restriction and may believe that you are temporarily facing a situation of starvation (because why else would you limit food so dramatically?).

However, for those who eat enough food when they do eat, the benefits of having a fasting window during which no food is eaten can extend beyond fat loss to balancing hormone levels, eliminating toxins and healing the body of diseases.  These benefits go above and beyond what a ketogenic diet can do on its own.


All About Fasting.

Eades, M (1970) Ketosis Cleans Our Cells.

Hofmekler, Ori (2001).  The Warrior Diet.  Dragon Door Publications Inc.  St. Paul, MN.

Stote KS, Baer DJ, Spears K, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. The American journal of clinical nutrition. 2007;85(4):981-988.

Varady, K. A., et al. (2009) “Short-Term Modified Alternate-Day Fasting: A Novel Dietary Strategy for Weight Loss and Cardioprotection in Obese Adults.” American Journal of Clinical Nutrition 90: 1138–43.

Whiton, J. (2012) The Whiton Protocol.