March 2, 2024

Introductory Disclaimer: What follows are my personal experiences and observations.  This information is for educational purposes only.  Although I am a physician, I am not your physician.  I am not providing you medical advice.  I am not a dietitian or nutritionist.  Before you consider taking any course of action similar to mine, consult with your physician.

Recently I completed a fast lasting 11 days, during which time I consumed zero calories.  I drank water and black coffee but took in no nourishment.  Notably, I never experienced hunger or a significant decline in function.  I lost approximately 25 pounds during the fast, but continued to work and do some wood splitting and manual labor during the period.  In truth, it was easy and I could have certainly extended the fast duration had I wished.

Why convey this information?  In a survival situation where food is scarce or absent, it may be helpful to be able to have the capability to function normally during an extended fast.

How is this possible?  How does a predator go for extended periods between successful hunts?  I would suggest the term “Metabolic Conditioning”.  Would you consider running a marathon if you never went for a run?  Of course not.  Similarly, you can prepare your body to adjust to a lack of food for prolonged periods with minimal disruption to your level of function.

Before getting into the specifics, just a little background information on how I arrived at this conclusion.

Approximately eight years ago, as a practicing physician in my mid-40s, I was diagnosed with cancer.  I was moderately overweight but had no other medical problems.  My treatment included high dose steroids, chemotherapy, and subsequent radiation therapy.

The steroid therapy accelerated the development of type 2 diabetes and my blood sugar levels were extremely high.  I began to develop the early stages of diabetic retinopathy with visual loss.

I found myself researching ways to improve my prognosis, reduce the negative effects of chemotherapy, and treat my diabetes.  I came across several websites discussing low-carbohydrate diets and intermittent fasting.  I significantly reduced my carbohydrate intake and then experimented with intermittent fasting, first eating in a six hour window and then also skipping one day a week altogether.  I took easy walks around the neighborhood.

I’m glad to report that intermittent fasting before treatments significantly reduced the negative side effects of chemotherapy.  Incredibly, I learned about that from an online patient forum and not my medical team. (Although I did pass the information along).

I lost nearly fifty pounds with only minimal exercise and my diabetes resolved completely without medication, despite my endocrinologist telling me I would certainly be on insulin.  My retinal changes resolved.  Amazingly, all that I did was reduce my carbohydrate intake and fast occasionally.

My cancer went into remission with treatment and has not since recurred.  My weight has been relatively stable although I did put on some pounds recently due to overindulgence, which led to my recent extended fast.  (Sorry, but I love bread.)

The Physiology of Fasting

A bit of physiology to explain how I did it.  We have two metabolic pathways by which we metabolize energy to function.  The first is our normal glucose metabolism pathway, where we use blood sugar and liver glycogen as energy.  This is the pathway most of us use exclusively, as we are never truly in a fasted state. It is associated with higher insulin levels.

The second pathway is the ketogenic pathway, where we burn body fat for energy.  This path is activated only after your blood sugar and glycogen levels are depleted, and is essentially atrophic in our modern diet in most people.  It is associated with low insulin levels.

The time for an individual to get into active ketogenesis varies, but certainly shortens after having undergone metabolic conditioning, wherein one repeatedly gets into ketosis.  In my case, it initially took a week, but now I fall into ketosis in one day after fasting.

You have certainly heard how runners “hit the wall” after they deplete their blood sugar and liver glycogen.  I read how runners in a ketogenic state generally don’t hit “the wall” because they have a massive caloric storehouse of body fat to use for energy.  They don’t run out of energy.

A physician named Jason Fung, who is a YouTuber and author, does a wonderful job of explaining low carbohydrate diets and intermittent fasting.  He describes how a high carbohydrate diet is like money in your wallet- it’s easy to get but only offers limited reserves.  In contrast, being in ketosis is like money in the bank – it’s hard to get out but there are far more resources available.  As an aside, much credit to Dr. Fung, who I’d encourage you to check out (no relationship to me).

Seeking Ketosis

You can get into ketosis by fasting, or by following a diet that is extremely low in carbohydrates.  This could be a “keto diet”, “Atkins diet”, or something similar.  In all cases, the common denominator for all these diets is that the diet results in very low insulin levels.

When we first try to get into ketosis, many feel horrible.  People describe “keto flu”, which I take to reflect that our blood sugar levels and glycogen stores are depleted but our ketogenic pathway is not fully active yet.  You might feel weak, foggy, or tired. Therein was my revelation.

In my case, I did a gradual progression to ketosis.  I reduced my carbohydrate intake to 10% of my total calories for a week or two.  Then I did a week or two with zero carbohydrates, eating meat, cheese, cream and butter. Occasionally I would take a break and enjoy some “normal food “, but try to keep my carbs modest.  Then I’d go back on a very low carbohydrate diet.

I added in an intermittent fasting component, eating only in a 6-hour window.  Eventually, I would also skip a day each week, often spontaneously.

In retrospect, I was slowly, repeatedly, conditioning myself to get into a ketogenic state easily and quickly.  It wasn’t a painful experience because I did it gradually.  Having done blood tests, I now know I can get into ketosis within a day of fasting.

Fasting Without Hunger

With respect to the extended fast, I was very rapidly in ketosis so I wasn’t energy deprived.  I didn’t experience any hunger because my body was burning fat for energy immediately.  Incidentally, the hunger hormone Ghrelin plummets during the first week of a fast, and your “hunger” markedly diminishes further.  (People who fast for longer periods are typically not hungry).

I did drink large amounts of water, because you lose 3 grams of water for every gram of fat burned.  You also lose electrolytes with your fluids, so a zero-calorie electrolyte supplement is a good idea to avoid cramps and headaches.

Be aware of the risks of re-feeding syndrome (Dr. Fung discusses this), because you may be at significant risk of this potentially fatal condition if you break an extended fast too rapidly (again, get professional advice on this and educate yourself.)  You must break an extended fast gradually and in a specific way to minimize your risk of injury.

What about muscle loss?  I’ve read and been informed that significant muscle loss typically occurs after around 40 days of fasting if the individual remains reasonably active.  In my case, I didn’t notice any negative consequences to my muscle mass.

Fasting Benefits

As an aside, there is significant evidence that the benefits of fasting can include longer lifespan, improved immune response, reduced cancer risk, improvements in type 2 diabetes, reduced dementia risk, and increase in native stem cell population.  An Internet search on the various aspects of fasting and the different fasting regimens may be illuminating.

In my specific circumstance, I have had a number of positive health benefits.  However, I was very surprised at how my metabolic conditioning,  by getting in and out of ketosis repeatedly, made undertaking an extended fast relatively effortless. I can’t imagine myself doing such a fast years ago.  Certainly, it seems like a nice ability to have in a survival situation.

For those who may have an interest in the health benefits of fasting, or if you perhaps value the ability to fast for extended periods without discomfort, my experience may be Food for Thought – pun intended.

JWR Added:  Coincidentally, this news article arrived in my e-mail inbox just as I was editing this article, for poublication:

The Source featured research by Valter Longo of the USC Leonard Davis School on how fasting for three days can improve a person’s health. The six-month study was done on subjects going through chemotherapy. “When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged,” Longo said.

(My thanks to long-time SurvivalBlog reader and frequent content contributor D.S.V. for the link.)