Intermittent Fasting – A Great Way to Right Your Metabolism, Lose Weight, Control Blood Sugar and Increase your Mental Alertness

Joseph E. Scherger, MD MPH

Amazon sells more than 5000 books on fasting, and many were written during this decade!  Fasting has exploded in popularity, and for good reason.  Fasting is a very healthy thing to do.

We can live for weeks, some of us for months, on no food if we have adequate water intake.  Prolonged fasting, more than three days, is not to be advised since that will cause some breakdown of your body other than fat. Intermittent fasting up to three days can be a very healthy thing to do.  When we fast, and drink water, we live off our body fat.  Even thin people with less than 10% body fat have enough fat energy to sustain themselves for days.  When you burn fat for energy, ketone bodies form, the breakdown product of fat.  This is also called nutritional ketosis. This is not to be confused with the state of ketoacidosis that happens in type one diabetics when there is no insulin to metabolize sugar.  The ketone bodies formed from burning fats are healthy and have great anti-oxidant properties.

I wrote about the ketogenic diet in my previous Blog so I will not repeat that here.  The ketogenic diet is regularly eating very low carbohydrates and foods rich in fat and protein.  Fasting is a nice complement to this and can jumpstart blood sugar control and jumpstart the body into burning fats for fuel.

There are several methods of intermittent fasting, and I regularly practice the first method.  I got some of this material from a self-published (on Amazon) short book by Steve Blum, Intermittent Fasting. Remember that ability to fast comfortably is enhanced by eating plenty of fat and protein form natural foods and avoiding the grains and sweets that drive hunger.  Remember to drink water! Coffee or tea without sugar (light cream is OK) may be included.

1.     12 hour intermittent fasting – This is the easiest method of fasting and fits into any lifestyle.  We normally fast while we sleep, but that is typically 6-8 hours.  The 12 hour fast means that you do not snack after dinner and you may delay breakfast some.  For example, finish eating at 7 PM and do not eat again until 7 AM.  If you have a later dinner for social reasons, delay breakfast until 12 hours later.  You may or may not lose weight with this method depending on what you eat during the other 12 hours.  Also, if you consumed a lot of carbs, including alcohol, at dinner, you may not go into a state of ketosis during the 12 hours so be mindful of that and avoid overeating and drinking.


2.     16 hour intermittent fasting – This is more serious fasting and may be done regularly or occasionally as a “cleanse”.  Here you reduce your food intake to two meals a day in one eight hour period.  For example you start eating at 11 AM or Noon and finish eating at 7 or 8 PM.  Blum suggests that women have a tendency to require more frequent eating and should strive for a 14 hour fast.


3.     5:2 Diet or The Fast Diet – This approach to intermittent fasting has you eating whatever you want 5 days a week and only eating about 500 calories 2 days a week.  It became popular in the UK by health journalist Michael Mosley in 2012 after his  documentary on the BBC called Eat, Fast & Live Longer. The diet quickly spread in Europe and the US.  Several books including cookbooks have been written about the 5:2 diet.  There is nothing special about this ratio, only that if you fast two days a week you will definitely get the benefit of intermittent fasting.  To fully benefit you should eat healthy foods all week, rich in fats and moderate protein.  If you eat too many carbs, your hunger will interfere with sticking to this diet and receiving the benefits.


4.     One to three days of intermittent fasting – Fasting for 24 hours or longer can be safely done up to three days, and the benefits are the same as listed for the ketogenic diet.  This length of fasting requires fortitude and limits how much physical activity you can do during this time.  I have not tried this but David Perlmuter MD (Grain Brain and Brain Maker) does this every three months. 

Whatever method of intermittent fasting appeals to you, I highly recommend you build this into your nutrition lifestyle.  It is a great way to rapidly return to a healthy state, especially after a period where you diet may not have been as good due to holidays or travel.