All About Intermittent Fasting, Chapter 1 | Precision Nutrition
Chapter 01 All about intermittent fasting, in under 10 minutes

Experiments with
Intermittent Fasting

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John Berardi, PhD photo
By John Berardi, PhD


Krista Scott-Dixon, PhD photo
Krista Scott-Dixon, PhD
Nate Green photo
Nate Green

Chapter 1

All about intermittent fasting, in under 10 minutes

Some experts claim short fasts can improve your health and help you lose fat faster. So we spent 6 months testing the most popular Intermittent Fasting (IF) protocols ourselves. Find out what IF is, whether you should do it, and if so — how.

For years, Dr. John Berardi, co-founder of Precision Nutrition, told his coaching clients to eat every 3-4 hours. That strategy — when combined with wise food choices, a smart exercise program, and world-class coaching — helped nearly 100,000 clients drop nearly 2,000,000 pounds of body fat.

Proponents of IF, on the other hand, reject the idea of eating so often.

Many say they’ve gotten healthier and leaner, faster, by deliberately skipping meals and sometimes going entire days without eating.

The IF research is intriguing, but young. Some animal and human studies suggest that IF may have benefits, but we don’t have enough long-term data to know for sure.

With research lagging behind at a snail’s pace, but enough anecdotal evidence to go from, we decided to do what we love at Precision Nutrition: test stuff ourselves.

Here’s what Dr. Berardi found, in his own words.

Why experiment with intermittent fasting?

I’m a professional dieter. In other words, I’ve done nearly every diet or nutritional protocol that’s around to test its efficacy.

Intermittent fasting has a small yet strong following and enough research to pique my curiosity.

I wanted to test it myself to see what kinds of physiological and psychological changes would come from it.

Also, as a competitive, masters-level track athlete and life-long fitness enthusiast, I wanted to test a new way to drop fat and get extremely lean, while staying strong and powerful.

What did you test?

Since there isn’t one definitive intermittent fasting protocol, I decided to test six different methods over the course of six months.

I kept meticulous notes on everything from scale weight, body-fat percentage, and blood/hormonal markers, to lifestyle markers like energy levels, cognitive thought, and pain-in-the-ass factors.

What happened?

Over the course of six months:

  • My weight dropped from 190 pounds to 170 pounds.
  • My body fat dropped from 10% to 4% while maintaining most of my lean muscle mass.
  • I found two intermittent fasting strategies that I could follow indefinitely with no problem.

Simply put, I hit the goals I set for myself in a way that was easier and less time-consuming than “traditional” dieting.

What are the big “takeaways”?

I think there are four main takeaways that readers of this book should come away with.

  1. Trial fasting is a great way to practice managing hunger. This is an essential skill for anyone who wants to get in shape and stay healthy and fit.
  2. More regular fasting isn’t objectively better for losing body fat. While my IF experiments worked quite well, the intermittent fasting approach (bigger meals, less frequently) didn’t help me lose fat any faster or better than a more conventional diet approach (smaller meals, more frequently) might have.
  3. More regular fasting did make it easier to maintain a lower body fat percentage. Intermittent fasting isn’t easy. However, I did find that using this approach made it easier for me to maintain a low body weight and a very low body fat percentage vs. more conventional diets.
  4. Intermittent fasting can work but it’s not for everyone, nor does it need to be. In the end, IF is just one approach, among many effective ones, for improving health, performance, and body composition.

So intermittent fasting is good, but not necessary?


Intermittent fasting can be helpful for in-shape people (who ideally have a healthy and sane relationship with food) who want to really get lean without following conventional bodybuilding diets, or for anyone who needs to learn the difference between body hunger and mental hunger. (And for the latter, I only recommend the Trial Fast.)

It’s a helpful tool and one I’ll continue to use periodically. But it’s not the end-all, be-all of nutrition or fitness.

People have been getting in awesome shape — and staying in awesome shape — for decades without the use of intermittent fasting.

How are IF and “grazing” similar?

Successful nutrition plans, whether they use smaller, more frequent meals (grazing) or larger, less frequent meals (fasting) all share a few features.

These include:

  1. Controlling energy intake. When we consume less energy (i.e. calories) than we burn, we lose weight (and, ideally, most of that is body fat). Whether you take in less energy by eating frequent small meals or infrequent larger meals is up to you.
  2. Focusing on food quality. Fresh, unprocessed, nutrient-dense food is a must, regardless of which eating style you adopt.
  3. Regular exercise. Exercise is a critical part of the equation.

Once those three have been taken care of, it’s a matter of personal preference and lifestyle considerations.

Here’s what the rest of this book will cover.

Chapter 2
Hi, My name is John. And I haven't eaten in 24 hours.
I tried not eating for 24 hours. I learned a lot, and so can you.
Chapter 3
Science or fiction? Exploring the benefits of intermittent fasting
What is IF actually supposed to do, and does it live up to the hype of its enthusiastic advocates?
Chapter 4
Why do intermittent fasting?
There are many reasons to explore IF. Here's what piqued my curiosity.
Chapter 5
Intermittent fasting review: Comparing the popular IF programs
IF means different things to different people. Here, I summarize and compare the most popular IF styles.
Chapter 6
The Weekly Fast: My first intermittent fasting experiment
Here's my starter IF protocol and what happened after the first few weeks.
Chapter 7
The Twice-Weekly Fast: When things go horribly wrong
I tried several different full-day fasting variations. Some worked, some didn't. Here's what I tried... and what went wrong.
Chapter 8
The Daily Fast: Back on track
Shorter, more frequent fasts are often considered more physique-friendly. I test whether that's true for me.
Chapter 9
Wrap-up, results, and lessons on self-experimentation
A summary of my results, with pictures, along with a discussion of why self-experimentation is cool, and how you can try it yourself.
Chapter 10
Appendix A: Cheat sheet with our 3 favorite protocols
Want to try intermittent fasting yourself? Here we summarize the three methods we like best and help you choose which is best for you.
Chapter 11
Appendix B: Intermittent fasting tips & tricks
A summary of the key Intermittent Fasting concepts and strategies, as well as the tips and tricks we cover in this book.
Chapter 12
Additional health, fitness, & nutrition resources
After reading about my experience, you may want to learn more. These additional health, fitness, and nutrition resources can get you started.
Chapter 13
Get to know the authors a little better
Find out who's behind the book... and the crazy experiments.

I’d like to learn more. What’s next?

Have 10 minutes? Read Appendix A. It’s a cheat sheet that shows you exactly how to do intermittent fasting, including specifics on our three favorite protocols.

Have 30 minutes? Read about the individual fasts in Chapters 67 and 8. Then read the cheat sheet in Appendix A. Then check out Appendix B for some tips and tricks we learned along the way.

Have an hour or two? Read the entire Experiments with Intermittent Fasting book. We spent a lot of time researching, conducting the experiments, and writing. We’d love to share it with you and hear your thoughts.


Chapter 2
Hi, My name is John. And I haven't eaten in 24 hours.
I tried not eating for 24 hours. I learned a lot, and so can you.

Love learning about food, health, nutrition, and fitness? Check out this FREE Best Diet report.

In it you’ll learn:

How to choose the best diet, for yourself or others.

The risks & rewards of paleo, keto, low-carb, and high-protein diets.

Our tested 3-step process for fixing any broken diet.

How to deal with common food intolerances/sensitivities.

And more, all taken from our research reports and studies.

With so many conflicting opinions out there, it can be tough to separate fact from fiction. Here’s your fast track to staying current and navigating trends.