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Summary
On episode 175 of 40+ Fitness, Coach Allan sits down with Dr. Jason Fung, who has treated thousands of obesity and type 2 diabetes patients and founded the Intensive Dietary Management Program, and Jimmy Moore, author of Cholesterol Clarity, Keto Clarity, and The Ketogenic Cookbook and host of several health podcasts, to discuss their book, The Complete Guide to Fasting.
Dr. Fung’s central argument is that fasting is simply the normal flip side of eating, not a punishment or an eating disorder, and that the “starvation mode” people fear actually comes from chronic calorie restriction, not from fasting itself.
Jimmy adds the practical, lived side of it, walking through his own extended fast (day 11 of 21 at the time of recording), the mistakes he made early on, and how becoming fat-adapted made fasting far easier over time.
Links
- https://www.intensivedietarymanagement.com
- https://www.dietdoctor.com
- https://periscope.tv/liveinlowcarbman
- Episode 77 – Jason Fung – The Obesity Code
- Episode 460 – Dr. Jason Fung on the mystery behind cancer
Key Takeaways
- Fasting is the normal flip side of eating, not a disorder. Dr. Fung says the word “breakfast” itself proves fasting is built into daily life; you can’t break a fast if you were never fasting to begin with.
- “Starvation mode” comes from calorie restriction, not fasting. Dr. Fung cites Biggest Loser research showing restricted-calorie dieters’ metabolisms dropped by roughly 700 to 800 calories a day and stayed suppressed for years, while a 4-day fast actually raised basal metabolism by about 10 to 12 percent.
- Fasting lowers hunger over time; calorie restriction raises it. Ghrelin, the hunger hormone, goes up under portion control but declines the longer a fast continues, peaking around day two and dropping after that, which is why fasting is more sustainable long term.
- Extended fasts get easier after the first couple of days. Jimmy describes hunger as brief “waves” rather than constant pain once the body fully shifts to burning its own stored fat.
- Being fat-adapted or low-carb makes fasting far easier. Dr. Fung says people coming from a high-carb diet struggle with fasting, while those already low-carb or ketogenic transition into it with little difficulty because their bodies already run efficiently on fat.
- Anorexia is a psychiatric body-image disorder, not something caused by choosing to fast. Dr. Fung pushes back on the common criticism, arguing that context (who is fasting, and why) determines whether it’s appropriate, not the act of fasting itself.
- Obesity is a hormonal problem, mainly insulin resistance, not just a calorie math problem. This is why the book frames weight loss around resetting hormones through fasting rather than counting calories.
- Stress and travel can sabotage a fast by spiking blood sugar. Jimmy says he once gained three pounds in the final two days of a 17.5-day fast purely from travel stress, and recommends planning extended fasts around calmer stretches.
- Practical fasting protocols range from intermittent to extended. The book lays out 16 to 24 hour intermittent fasts, roughly 36-hour alternate-day fasts, and multi-day extended fasts, often supported with bone broth and electrolytes rather than diet soda.
“Fasting is merely the flip side of eating.”
Dr. Jason Fung