How My Opinion of Fasting Changed After Talking to Dr. Jason Fung

Key Takeaways

Dr. Jason Fung describes how his views on fasting have evolved and argues that appetite, hormones, food environments, and habits matter more than calorie counting alone. The points below reflect the speakers’ interpretations of research. Some claims—especially those concerning prolonged fasting, cancer, and dementia—are preliminary and should not be treated as established treatment advice.

• Modified fasting may be easier to sustain than water-only fasting. Fung discusses approaches such as a five-day fasting-mimicking diet of roughly 800–1,000 calories per day and “fasting aids” such as tea, coffee, broth, olives, or avocado. He suggests these may make fasting more manageable while retaining some benefits, but they are not water-only fasts.
• Make fasting sustainable, not a test of endurance. Fung says a modest aid may help someone continue longer, and that a repeatable routine is more useful than one they dread. He discusses approaches ranging from daily eating windows to 36-hour fasts and longer modified or water-only fasts.
• Understand different kinds of hunger. Fung distinguishes:
  • Homeostatic hunger: Physical hunger related to the body’s energy needs.
  • Hedonic hunger: Eating for pleasure, comfort, or reward.
  • Conditioned or social hunger: Cravings prompted by routines, cues, or other people’s eating habits.

He suggests identifying what is driving the urge to eat before deciding how to respond.

• Reduce ultra-processed foods. Fung’s main recommendations are to limit ultra-processed foods, establish times when you do not eat, and build a supportive social environment. He argues that highly processed foods can encourage reward-driven eating.
• Use routines and social support. Setting a clear eating window—for example, not eating after dinner—may help interrupt habitual or cue-driven eating. Supportive friends, family, or groups can make changes easier to maintain. Social plans such as walks can offer alternatives to food-centered gatherings.
• Choose minimally processed foods when eating. The speakers discuss prioritizing real foods and making the first meal after a fast nourishing, with protein, fiber, and healthy fats. Fung also mentions food order, meal timing, walking after meals, and cooled-and-reheated rice as additional, smaller considerations.
• Consider hormones and life stage. Fung argues that insulin and sex hormones can affect hunger and how the body stores fat. The speakers discuss changes in appetite and fat distribution during the menstrual cycle and perimenopause, and caution against treating weight changes as simply a matter of willpower.
• Treat fasting research cautiously. Fung points to research on longer fasts and modified fasting, including possible effects on inflammation and other health markers. He also discusses fasting as a possible adjunct to cancer care—not a replacement for chemotherapy or other prescribed treatment—and acknowledges that some potential benefits remain preliminary.
• On muscle, emphasize use as well as nutrition. Fung argues that exercise and muscle use are central to building or preserving muscle, and recommends real food rather than relying on protein products. The conversation also emphasizes eating adequately when refeeding.
• Weigh the trade-offs of weight-loss medication. Fung says GLP-1 medications can reduce hunger and may have a role, but discusses side effects, reduced enjoyment of eating, discontinuation, and weight regain. He argues that addressing eating habits and social or emotional triggers matters too.
• Visceral fat and fasting. Fung distinguishes visceral fat around organs from fat beneath the skin and argues that fasting and low-carbohydrate eating can reduce liver and visceral fat. These are his explanations of the evidence, not individualized medical guidance.

Caution: The conversation discusses multi-day fasting but does not provide individualized screening or safety advice. Anyone considering prolonged fasting—particularly people with medical conditions or those taking medication—should consult a qualified healthcare professional.

Presenters and Sources Mentioned

• Presenters: Dr. Mindy Pelz and Dr. Jason Fung
• Books by Jason Fung discussed: The Obesity Code, The Complete Guide to Fasting, and The Hunger Code
• Other people or programs mentioned: Megan Ramos and The Fasting Method; Dr. Valter Longo and the fasting-mimicking diet; Michael Mosley and the 5:2 diet; Terry, a psychologist and coach with The Fasting Method
• Research bodies, publications, and studies cited: Women’s Health Initiative; National Institutes of Health trials; American Heart Association; a seven-day water-fasting study the speakers associate with Nature or Nature Medicine; and Kaiser Permanente real-world data on GLP-1 medication use.