One aspect of eating a very low carb diet  is that it is much easier to skip meals.  The intense hunger that demands to be fed, caused by low blood sugar and a brain that is totally dependent on that sugar, is no longer present.  The brain is just fine, in some sense better off, fueled by ketones, the fuel derived from fat stores and manufactured by the body. For the small amount of glucose that your body needs, it can be manufactured from byproducts of the stored fat that's being burned, as well as from the protein in lean tissue.  When I skip meals, I do still feel "empty" around the time I normally would eat, mostly out of habit more than anything else, but this passes quickly, and is usually replaced by a feeling of increased energy.

Since I've started this approach to eating, I've found myself naturally missing meals or even fasting for up to 20 - 30 hours.  I find these fasts to be quite easy and actually enjoy the feeling of energy and mental focus they provide, likely due to the increased level of ketones in the blood.

Some have extended these fasts much longer.  For example, Jimmy Moore, of "Livin' La Vida Low Carb" fame, has done a couple much longer fasts, and tracked the results with a great amount of detail.  You can read about the 3 day fast he initially did, and the 18 day fast he just recently completed.  (He hasn't blogged about that fast yet so the link takes you to one of the periscope videos that he did about it.)

My October-Fast

Last month I decided to try a more extended fast than I've done previously to see how it would go.  There are a lot of reasons to do a fast.  When people ask "why would you want to fast?" these are the things I think about.

  1. Not consuming any protein or other nutrients used to build and maintain cells, forces the body to use other sources in order to continue the normal process of rebuilding tissue.  One way it does this, is to trigger a process called autophagy.  This is a process that triggers damaged cells to be torn down, releasing the material of the cell to be used to rebuild other parts of the body.
  2. There is strong evidence that periodic extended fasting can help stop cancer cells that may be hiding in the body and could later develop into full-blown tumors.  This is in part based on the theory presented by Dr. Thomas Seyfried, and based on research he and others have done as well as a theory that was first proposed in 1924 by Otto Warburg.  (If you really want to study this theory in significant technical detail you can read Dr. Seyfried's book; Cancer as a Metabolic Disease.  Note that this is a sponsored link.) Put simply, the Warburg Hypothesis says that primarily, cancer starts with the failure of the mitochondria in cells such that they can only inefficiently process glucose for fuel and not fats.  This makes them highly dependent on glucose (as well as being susceptible to rampant mutation since there's not sufficient energy to maintain the cell's nucleus.)  Therefore, a fast is a good way to kill off any latent, damaged, precancerous cells.  
  3. Fasting is believed to increase insulin sensitivity.  This is more or less the opposite of metabolic syndrome which is characterized by insulin resistance.  An advanced outcome of metabolic syndrome is type 2 diabetes.  Dr. Jason Fung is a strong proponent of extended fasting as an effective treatment for type 2 diabetes, going so far as to assert that type 2 diabetes is completely curable through fasting.  I'm beginning to believe that even a good dietary approach like very low carb, consistently practiced over a long period of time, can lead to increased insulin resistance and lower metabolism.  Thus, fasting might be a good way to make a change to the diet to trigger positive results.  (I'm seeing a number of different approaches to changing the diet all claiming to improve insulin sensitivity through changing the diet.  I'm working to understand it better and might have a post in the future about it.)
  4. Growth hormones may be increased by fasting.  This can help reduce some of the effects of aging.
  5. It is good to know that I can do it.  Beyond just the simple challenge to see what happens, its good to know that if I ever needed to, I could easily go without eating for an extended period of time.  I would know what the effects are and what it feels like and I would know what things I would have to try to do to prevent problems (like staying hydrated.)  So if the Zombie Apocalypse happens, I'll be prepared!
  6. I got a device called a "Ketonix" which is basically a breathalyzer that can monitor the presence of ketones in the breath.  This a simpler and ultimately cheaper means to estimate the level of ketones in the blood.  The other way is to use expensive test strips.  In order to use this device though, it really needs to be calibrated and it's likely that calibration is different for everybody.  This fast then was a way to get a wide range of blood ketones in myself, measure them with the ketonix and test strips, and develop my own calibration curve.  (I don't believe that everyone needs to constantly test their ketones to successfully follow these nutritional approaches.  I do this because I have an intellectual curiosity and like to measure and study.)

How I did the fast

For this fast, it was not quite a "water fast" in which one consumes only water and no food or other nourishment.  Instead, I did continue to drink coffee with a little heavy cream and "Sweet Leaf" brand stevia sweeter.  As much as anything, I did that simply because I like coffee, and it added negligible nutrients to my fast.  Heavy cream is almost all fat and very little protein so it should not negate any of the beneficial aspects of the fast.

The last substantial food I consumed, the morning I started the fast, was a cup of coffee with 2 T each of MCT oil and grass feb butter dissolved in it, typically called "bulletproof coffee."  This drink triggers the production of ketones, which is one of the key intents of the fast, so I wanted to jump-start the process.

One of the side effects of fasting is dehydration, so I made sure I drank plenty of water, in addition to the coffee, and supplemented with potassium, magnesium, and consuming several pinches of sea salt while drinking water a couple times a day.

How I Felt

Overall, I felt fine throughout the fast.  I felt like I was keeping hydrated enough because I didn't experience any of the downsides of that (headache, fatigue, etc.)  I will note that the night after the fast I did experience a leg cramp.  Leg cramps can typically be caused by loss of electrolytes or dehydration so I may have gotten a little depleted in that regard.

I periodically felt hungry, but this passed quickly, and I never felt as if I was weak or shaky as from low blood sugar even though it dropped to a low if 59 mg/dL during the fast.  While I always felt like I had enough energy, and that I could do anything I needed to do, I didn't feel like I had any great surge of energy like I do with a 20 hour fast.

In the last 1/2 day or so I really felt like I wanted to eat.  I seemed to crave food.  In all this I didn't feel like I had to eat though, I just thought like I wanted to.  In my mind I had planned to go for 3 days.  I think this craving was driven mostly by the knowledge that I did plan to eat soon and I was therefor looking forward to it.  The only way to really know, would be to extend the fast farther and see how I feel.

Ending the fast, I knew that I wanted to take it easy and not eat a large meal.  In shorter fasts I've done, I learned that my system doesn't like to eat a large meal right away.  I ended this fast with some macademia nuts, a small piece of aged gouda cheese, a scrambled egg cooked in a little butter, and glass of kombucha, waiting a little while between each to make sure my system was handling them well.  An interesting observation is that the nuts and cheese tasted good, but when I tasted the scrambled egg it somehow tasted like the best thing I had ever eaten.  It was an interesting and unexpected experience.  It seemed as if my body was definitely missing the formidable nutrients that are in eggs and very much appreciated them.

Tracking (Warning - This is the "sciencey" section)

To track this fast, I regularly measured blood glucose, blood ketones, and breath ketones using the ketonix.  I've inserted graphs of each of these variables below, showing the effect the fast had.

This graph shows my blood glucose measurements over the three days of the fast.  The first reading was around noon of the first day, after the fast had begun.  The last reading was one hour after having a small meal to end the fast.  My blood glucose dropped to a low of 59 mg/dL before ending the fast.

This graphs shows the blood ketone measurements I made throughout the 3 day fast and then for  a couple days after the fast.  There is a steady rise in ketones from my typical level on my low carb diet of around .5 mmol/L.  My ketones got as high as 3.7 mmol/L before ending the fast.

I was able to calculate a fairly good correlation between the Ketonix breath ketone readings and blood ketones over the course of the fast.  I only used readings during the fast (as ketones were increasing) rather than after the fast (as ketones were decreasing) because of what I observed below.

By using the correlation I developed from the data during the fast, I was able to make the graph above that shows an equivalent blood ketone level as predicted by the Ketonix.  This graph can be compared to the graph of measured blood ketones.  After the end of the fast, the blood ketones drop quickly, returning to normal within 2 days.  The breath ketones took a full day longer to drop to normal.

This can be understood by knowing what the blood ketone strips measure (beta-hydroxybutyrate) and what the Ketonix measures (acetone.)  From this fast it became clear that acetone stays present longer, after the beta-hydroxybutyrate is depleted.

Summing it up

Overall this was a good experiment.  I was able to calibrate my breath ketone measurements, completed a 3 day fast with no ill effects and feeling fairly good, and I got some interesting data.  I expect that I'll do this again, probably once or twice a year, and may try a longer one to see what happens.  Before that though, I plan to do a different experiment.  This is with a diet approach called "The Carb Nite Solution."  This is an approach I've known about for a couple years and have been very interested in, but have yet to try.  A number of things I've been curious about have led me back to thinking about that approach and I plan on testing it myself to see what happens.