The Complete Guide to Fasting (Dr. Jason Fung): Book Overview

The Ultimate Manual for Therapeutic Fasting

While Dr. Jason Fung’s first book, The Obesity Code, focused on the deep endocrinology and theory of why we get fat (insulin resistance), his follow-up book, The Complete Guide to Fasting, co-authored with Jimmy Moore, is all about execution. It is the practical, hands-on manual for anyone looking to use fasting as a therapeutic tool to heal their body.

Whether you want to lose a few stubborn pounds, reverse type 2 diabetes, or explore the longevity benefits of extended water fasts, this book provides exact schedules, troubleshooting tips, and medical protocols to do it safely and effectively.

Expert Take (Aly Owen): “This book is the gold standard reference manual. Whenever a client asks me a specific question—like how to fast if they are on medication, or what to do if they get a headache on day two of a fast—the answers are always found in this guide.”

Fasting as an Ancient Healing Tradition

Dr. Fung begins by removing the modern stigma associated with fasting. He points out that for thousands of years, fasting was considered a natural, healing practice in almost every major religion and culture. It is only in the last 50 years—with the advent of the food industry’s push for 3 meals and 3 snacks a day—that fasting became viewed as “starvation.”.

The book clearly distinguishes between starvation (involuntary, uncontrolled absence of food) and fasting (voluntary, controlled abstinence for spiritual, health, or other reasons). Your body is perfectly designed to survive and thrive during periods without food by seamlessly switching to burning its own fat stores.

Practical Protocols for Every Goal

The Complete Guide to Fasting excels in its detailed breakdown of different fasting protocols. It does not force a one-size-fits-all approach. Instead, it offers options based on your specific health goals:

• 16:8 or 20:4 (Daily Fasting): Ideal for steady, long-term weight loss and general health maintenance.
• 24-Hour and 36-Hour Fasts (Monk Fast): Recommended for breaking through weight loss plateaus and reversing severe insulin resistance.
• Extended Fasts (3 to 7+ Days): Used therapeutically for massive autophagy, immune system resetting, and rapid reversal of type 2 diabetes (must be done under medical supervision if on medication).

Troubleshooting the Side Effects

One of the most valuable sections of the book deals with the common side effects of fasting and how to manage them. Dr. Fung and Jimmy Moore address real-world challenges that cause people to quit prematurely.

For example, if you experience headaches or muscle cramps during a fast, the book explains that this is usually due to sodium and electrolyte depletion (as fasting lowers insulin, which causes the kidneys to excrete water and sodium). The simple fix? Drink some bone broth or add a pinch of sea salt to your water. They also provide practical advice for dealing with hunger waves, dizziness, and constipation.

Key Takeaways from The Complete Guide

• Bone Broth is Your Friend: On longer fasts, homemade bone broth provides essential electrolytes and makes the fast highly sustainable without breaking the benefits.
• Feast Properly: Breaking an extended fast is just as important as the fast itself. Start with a small, easily digestible meal (like a handful of nuts or a small salad) to avoid gastrointestinal distress.
• Don’t Force It: If you feel unwell, dizzy, or nauseous (beyond normal hunger waves), break the fast. Fasting should be therapeutic, not torturous.
• Combine with LCHF: Fasting is most effective when combined with a Low-Carb, High-Fat (LCHF) or Ketogenic diet, as both strategies keep insulin levels low.

Frequently Asked Questions

Is fasting safe for type 2 diabetics?
Yes, Dr. Fung uses fasting extensively in his clinic to reverse type 2 diabetes. However, if you are on medications (especially insulin or blood sugar-lowering drugs), you MUST consult your doctor before fasting, as your medication doses will need to be adjusted to prevent severe hypoglycemia.

Will fasting slow down my metabolism?
No. The book cites numerous studies demonstrating that while daily caloric restriction slows the metabolism, intermittent and extended fasting actually boosts basal metabolic rate due to increased adrenaline and noradrenaline.

What can I consume during a fast according to this guide?
Dr. Fung is slightly more lenient than the strict “clean fast” crowd. He allows water, black coffee, plain tea, and, for those struggling, small amounts of bone broth or a tiny splash of heavy cream in coffee to help compliance.

Aly Owen

Certified Nutritionist & Fasting Expert

Aly Owen is a certified nutritionist and intermittent fasting expert. With over 8 years of clinical experience, she specializes in metabolic health and sustainable weight loss through fasting. Aly breaks down complex science into actionable advice.