Fasting as a Reboot — Confessions of a Supply-Side Liberal

In wartime, during heavy fighting, when replacement parts are hard to come by, soldiers often given up on some of the vehicles, and strip those vehicles for parts to use in repairing other vehicles. This is called “cannibalizing” those vehicles whose parts are stripped.

Similarly, when the body finds nutrients scarcer because you are fasting (for example, not eating anything, but only drinking water), it gives up on certain molecules and even whole cells and cannibalizes them for spare parts. Then when you are eating again and nutrients look more abundant to your body, new molecules and even whole cells are constructed. Because the body is judicious in which molecules and cells it cannibalizes, fasting fosters a type of quality control for the body. The new molecules and cells are generally of higher quality than the ones that have been cannibalized. Thus, fasting, followed by eating again results in a type of renewal, or a “reboot,” to use a computer metaphor.

One of the easiest places to see the reboot in action is by looking at the white blood cells. The blog post “Study Finds Fasting For 72 Hours Can Regenerate The Entire Immune System” by Elizabeth DeVille reports on some research confirming the reboot for white blood cells.

Another, quite distinct way in which fasting is a reboot is that it seems to reset the production of hormones such as insulin and ghrelin. Evolutionarily, it didn’t make sense for your body to distract you with debilitating hunger when no food was available, and our ancestors faced plenty of periods of time with no food available. Our ancestors didn’t face “dieting” in the sense of eating reduced quantities of “modern” foods that have only existed relatively recently. In other words, our bodies are well-designed for periods of no food, but not well-designed for modern foods. Periods of no food that our body is well-designed for can help our body get its bearings.

So-called “paleo” diets focus on what kinds of foods were available long ago. But the temporal pattern of eating long ago—including substantial periods of no food—and the rarity of some foods that were available—for example, honey in only small amounts and that quite seldom—are also very important to pay attention to. Paleo diets have some useful ideas, but they are also missing some other key ideas.

On trying get insulin levels into a good range, see “Obesity Is Always and Everywhere an Insulin Phenomenon.”

On ghrelin, let me quote from the blog post “7 Benefits of Fasting and the Best Types to Try for Better Health” by Kissairis Munoz:

5. Fasting can normalize ghrelin levels.

What is ghrelin? It is actually also known as the hunger hormone, because it is responsible for telling your body that it is hungry. Dieting and really restrictive eating can actually increase ghrelin production, which will leave you feeling hungrier. But when you fast, though you might struggle in the first few days, you’re actually normalizing ghrelin levels.

In other words, fasting won’t be as hard as you think; it can be much easier than dieting in the sense of just trying to eat less of what you usually eat. (Eating low-insulin-index foods is the key to making eating less easier and to making the first day or two of fasting easier. See “Forget Calorie Counting; It's the Insulin Index, Stupid.”)

Before getting serious about fasting, there are important things for you to know. I have links to my diet and health posts organized in “Miles Kimball on Diet and Health: A Reader's Guide.” Within that bibliographic post, I have a section of links to posts particularly on fasting. Here are those links copy-pasted:

II. Fasting