How To Intermittent Fast: An Exploration of Fasting Protocols

How To Intermittent Fast: An Exploration of Fasting Protocols

During the season of holiday feasts, the Qualia team and community seem compelled to find balance with fasting. One member is following a fast mimicking diet (FMD), others are doing time-restricted feeding protocols, and two are doing extended multi-day fasting. We found the same pattern in the so we wanted to create a four-part series to share with you some of the science, what you can expect, and how to do fasting.

For those interested in doing a deep dive into different fasting regiments, Science published a first-rate article called “A time to fast” on November 16, 2018. We’d like to distill some of the key concepts in a digestible format, but also provide anecdotes from the Qualia team. These provide context for real-world experiences you may face outside a laboratory. 

In this article, we’ll provide the big picture of fasting and historical background of the early research. In What to Expect While Fasting we cover the different methods of starting and why the Qualia team feels compelled to fast (and what their experiences might mean for you). For more information, check out our videos from our Facebook Q&A events on How to Fast and the Fast-Mimicking Diet. Check out our Facebook event page to join us for future Q&As to ask any question you might have including: How can you start a fast? What is fasting? Is fasting healthy? What are the top fasting benefits?

Some Fasting Basics

Let’s start with some basics. Fasting is as old (if not older1) as the human species, brought on by necessity when food was scarce in a hunter-gatherer environment. Our genes evolved to respond to times of plenty and times when food is less abundant. 

While our physiology evolved alongside periods of feast and famine, modern agriculture and supply chains have made food scarcity, outside of the context of poverty or weight loss diets, rare. This might be causing a mismatch between what our genes evolved to do and what we are actually causing them to do. 

In the traditional use of the word, “fasting” generally applies to complete abstinence (more on that below). When abstaining from all food, the body undergoes specific physiological changes. According to Dr. Jason Fung (author of The Complete Guide to Fasting) a general timeline after starting a fast includes:

  • Eating produces higher levels of insulin, which is a hormone that signals the body to store food energy (either in the liver or in fat cells). When we miss a meal insulin signaling decreases.

  • First 24 hours: Because dietary energy is no longer present, glycogen (a storage form of sugar used for quick energy) stores are broken down and used for energy.

  • 24 - 36 hours: The body breaks down proteins more aggressively to convert them into sugar molecules (a process called gluconeogenesis). The body may also start selectively eliminating damaged or dysfunctional cells and mitochondria at this point (this is called autophagy and we discuss it more in Anti-Aging Benefits of Fasting).

  • 36 hours and after: The body’s mechanisms that convert fat into energy start to take over and we begin to function on stored fat. Most people enter ketosis by about the start of this period or shortly after.

Keep in mind that the physiological processes that occur over the first several days are highly dependent upon the individual. As they say in the biohacking community YMMV (your mileage may vary) the actual physiological response will fall on a spectrum (some people enter ketosis quicker and others more slowly) because of factors including genetic reasons and past experience with fasting.

How to Fast

There is no one-size-fits-all fasting protocol. Many people try different methods before settling on their favorite. As the Science article indicates, fasting-feeding regimens fall into four categories: 

1. calorie restriction
2. time-restricted feeding
3. intermittent (periodic fasting)
4. fasting-mimicking diet

Descriptions of each are summarized below.

Calorie Restriction

As with many novel health interventions, the early variations of calorie restriction (CR) left much to be desired. The classical form of calorie restriction indicates “daily caloric intake is typically decreased by 15 to 40%...”2 

At first glance, a 15 - 40% reduction in calories doesn’t seem so bad. Humans consume an average of 2,000 calories per day. To reduce that number by 15 - 40% would equate to 1200 - 1700 calories. Human experiments suggest this is challenging to sustain long-term, however.

In the 1944 - 1945 Minnesota Starvation Experiment, participants went through 24 weeks of calorie restriction where scientists discovered increased rates of depression, hysteria, and severe emotional distress.3

A pair of modern researchers took the Minnesota Starvation Experiment data and further analyzed the effects on the mind based on their understanding of what occurs when the brain must deal with scarcity. Upon closer inspection, Eldar Shafir and Sendhil Mullaianathan (co-authors of Scarcity: Why Having Too Little Means So Much) found that the semi-starvation diet disrupted cognitive performance. Participants of the study couldn’t stop thinking about food and eating. An April 2018 NPR Episode of Hidden Brain recounts how even when researchers provided films to distract subjects from their hunger, participants desperately sought food-related scenes.4

As the participants of the Minnesota Starvation Experiment found out, it’s one thing to consume 15 - 40% fewer calories for a weekend, but it is something altogether different to do so for months at a time. 

If living an entire life eating 15 - 40% less than your body craves seems unappealing, you’re in luck. It’s possible to restrict meal size or meal frequency without a long-term reduction in caloric intake. In theory, this should provide most (if not all) the benefits of traditional calorie restriction, but without harmful effects.

These interventions are the subject of What to Expect While Fasting where we explore the current, real-world applications of fasting, how to fast, and what to expect.

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For more information on the topic, see our related podcasts:


1 We can safely assume our primate ancestors had periods of food scarcity.
3 Tucker, Todd (2006). The Great Starvation Experiment: Ancel Keys and the Men Who Starved for Science. New York: Free Press.
4 The segment is between ~ 08:30 - 13:50. 

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