Welcome to Keto Sister.  If you have not read my intro series titled Keto Basics, then please click here to review the benefits of a ketogenic (keto) diet, steps for how to get into ketosis and what eating keto looks like day to day.  Eating a keto diet, one that is high in dietary fats (65% of calories or greater) with moderate protein intake (15-25% calories) and minimal carbohydrates (5-10%), has many benefits that make fat loss relatively easy.  Among the benefits is how easy it is to fast.

Nutritional ketosis (defined as having 0.5-3.0 mmol/L of ketone bodies in the blood [Volek & Phinney, 2012]) often creates a feeling of satisfaction with eating less food.  The first sign that I was in ketosis was that my usually insatiable hunger went away.  I learned from a trainer years ago to keep my metabolism activated by eating three meals with three snacks in between, and it stuck because I was hungry if I did not eat every few hours.  But suddenly, after following a keto protocol for a couple weeks, I found myself skipping lunch by accident.

I am not the type of girl who skips a meal without having a very good reason not to eat (reasons like strep throat or child birth!).  With a keto diet, however, skipping a meal is easy to do.  Meal skipping is also called fasting.

Fasting or starving?

People often confuse fasting with starvation, but there is a metabolic difference.  Starvation is a state of metabolic shut down that occurs when a person who does not have any body fat does not eat food, usually because food is not available.  Also called starvation mode, a person can induce the symptoms of starvation by undereating by too many calories and/or overtraining despite having plenty of body fat (see Deficit to learn more).  Starvation results in the body breaking down essential components (like muscle) for energy in the absence of body fat or food.  In addition to breaking down essential components, starvation can result in the down-regulation of a number of bodily functions including amenorrhea, hypothyroidism, hair loss, muscle fatigue, and many other very scary conditions (McCue 2012).

Fasting, on the other hand, is when a person with some amount of body fat could eat food but chooses to abstain between meals.  When a person does not eat for up to 24 hours, the window during which they do not eat is called an intermittent fast (more details in the section below).  Not eating for 24 hours or longer is a prolonged fast.  However, essential functions continue effortlessly during a fast because the body has an energy source in the form of body fat to meet the body’s needs.  Also, when the fast ends, the person resumes eating a healthy amount of food.  This is a critical difference between starvation and fasting because if a person fasts and then undereats, he or she may soon develop the symptoms of starvation listed above.  This occurs commonly among low carb dieters who eat at too large of a deficit, but I explained how to avoid this in last week’s post.

But why, you may be wondering, would a person who can eat ever choose not to?

Benefits of Fasting

Reduce hunger levels.  You read that right.  Fasting helps to reduce hunger levels.  How can eating less often make you feel less hungry?  Klock and colleagues (2007) found that ghrelin levels, which is the hunger signal in the body, are highest in obese individuals.  Fasting has an almost magical effect on ghrelin, causing it to decrease and help individuals feel less hungry.

When fasting is combined with keto eating, which by itself helps to stabilize glucose levels and is a very satiating eating strategy (Dashti et al., 2004), then hunger levels are easily reduced to the point that even people who are normally very hungry will find themselves skipping meals.

Drop excess body fat.  When a person who fasts has access to food and chooses not to eat, the person’s body supplements the body’s nutritional needs.  Many people who fast do so because fasting decreases body fat.  Klock and colleagues (2007) also found that leptin levels, which signal the body to release body fat stores, are lowest in obese individuals.  Fasting increases leptin levels and induces the body to release its fat stores.  Dr. Jason Fung, whose practice has used fasting as a methodology for treating insulin resistance and obesity in 800 patients, cites two studies which found that daily fasting—eating fewer meals per day—resulted in minimal muscle loss (Bhutani et al., 2010; Stote et al., 2007).  His clinic prescribes fasting to type 2 diabetics, obese patients, and those with insulin resistance because of how effectively fasting can bring a body into balance (see Intensive Dietary Management for details).

Fasting in ketosis spares muscle loss.  When a person who is in ketosis fasts, because the body is already adapted to burning both dietary and body fat, almost no muscle mass is lost.  Very low carb diets are muscle sparing (Manninen, 2006), and the body has an incredible adaptation mechanism that allows glucose, protein and fuel needs to be converted from the body during a prolonged fast.

The table below (Hall, 2016) demonstrates what happens when a person fasts and the amount of each macronutrient that can be produced by the body during a state of fasting.  This, of course, only applies to the body of a person with sufficient physical mass and some body fat.

Reduce serum glucose and insulin levels.  Of particular interest are the effects of fasting on blood glucose and insulin levels.  Eating a ketogenic diet mimics the effects of fasting and is an alternative way to meet many of the same goals.  However, fasting is a fast way to improve these markers and does not require eating a ketogenic diet (though the combined effects can be even more profound).  The table below shows improvements in fasting blood glucose levels, insulin levels, and the body’s ability to respond (insulin sensitivity) or ignore insulin (insulin resistance) when it is released to reduce glucose levels.  Diabetics have high glucose levels which reflects insulin resistance, a problem that fasting easily reverses.

Autophagy.  Another benefit of fasting is protein recycling and cellular clean up.  Fasting allows the body to induce a state of autophagy, during which the body recycles old protein matter (“junk”) within the cells and uses this to meet protein needs.  Autophagy is a process that is believed to increase longevity and prevent conditions such as cancer due to the elimination of the excess junk matter (see Rob Mignery, Protein Cycling Diet for details).  One form, chaperone mediated autophagy (CMA), is activated simply by generating and using ketone bodies (see Eades, Ketosis Cleans Our Cells).  Everyone eating a ketogenic diet induces this form of autophagy on a constant basis, simply by keeping carbohydrate consumption very low and generating ketone bodies.

Two other forms are microautophagy and macroautophagy.  These forms of autophagy are triggered by restricting dietary protein.  One way to restrict protein is to minimize protein intake in addition to carbs, as suggested by Josh Whiton (see The Whiton Protocol), while still consuming large amounts of fat.  Another is to do a complete caloric fast, such as a water fast or calorie free liquids only.

Other benefits of fasting, according to the website “All About Fasting,” can include:

  • Healing health disorders.
  • Cleansing the body of metabolic wastes and toxins.
  • Improving skin tone and health.
  • Stimulating new cell growth.
  • Strengthening the immune system and natural defenses.
  • Improving glandular health and hormonal balance.
  • Increasing mental clarity.
  • Enhancing moods and providing a natural boost.
  • Increased energy and vitality.

Learning about the possible benefits of fasting motivated me to learn more about it and to experiment.  But the reason I began fasting in the first place was because I kept forgetting to eat lunch.  I had ketosis to thank for this and began to see it as an opportunity.  Meal skipping while not being hungry is not a bad problem to have, as long as the person eats a good amount of food during meal times (see Deficit for details on how much to eat for fat loss without overdieting).

One final important note is that fasting is not for those who are new to ketosis, pregnant, breastfeeding or struggling with other stressors because it can make those stressors worse.  However, for those who are healthy, it is a wonder way to reduce insulin levels and shed excess body fat.  When your hunger falls away naturally and you find yourself naturally skipping meals, then you are ready to explore the many wonderful possibilities that fasting has to offer.


All About Fasting: Using Fasting for Natural Healing.  http://www.allaboutfasting.com/ 

Bhutani S et al. (2010) Improvements in coronary heart disease risk indicators by alternate-day fasting involve adipose tissue modulations. Obesity. 2010 Nov; 18(11):2152–9.

Dashti, H. M., Mathew, T. C., Hussein, T., Asfar, S. K., Behbahani, A., Khoursheed, M. A., … Al-Zaid, N. S. (2004). Long-term effects of a ketogenic diet in obese patients. Experimental & Clinical Cardiology9(3), 200–205.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2716748/.

Fung, J.  (2016) Intensive Dietary Management.  https://intensivedietarymanagement.com/

Hall, K. D. et al. (2016). Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men. The American Journal of Clinical Nutrition95(4), 989–994. http://doi.org/10.3945/ajcn.112.036350.

Klok, M. D., Jakobsdottir, S. and Drent, M. L. (2007), The role of leptin and ghrelin in the regulation of food intake and body weight in humans: a review. Obesity Reviews, 8: 21–34. doi: 10.1111/j.1467-789X.2006.00270.x

Manninen, A. H. (2006). Very-low-carbohydrate diets and preservation of muscle mass. Nutrition & Metabolism3, 9. http://doi.org/10.1186/1743-7075-3-9

McCue, M. D. (2012). Comparative physiology of fasting, starvation, and food limitation (pp. 103-132). New York: Springer.

Mignery, R (2009) Protein Cycling Diet.  https://proteincyclingdiet.wordpress.com/

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

Volek, J. and Phinney, S. (2012) The Art and Science of Low Carbohydrate Performance.  Beyond Obesity LLC. 

Whiton, J. (2012) The Whiton Protocol.  http://joshwhiton.com/health/autophagy/