Dr. Jason Fung Changed His Mind About Fasting - Here’s Why

Summary

Dr. Jason Fung says his views on fasting have evolved as more research has emerged. He discusses evidence on longer and modified fasts, and argues that fasting can be made more practical through approaches that are easier to sustain. The health benefits described in the interview—especially for inflammation, cancer, and dementia—are presented as emerging or preliminary, not settled medical guidance.

Strategies and techniques discussed

• Consider modified fasting rather than water-only fasting. Examples discussed include:
  • The 5:2 approach: five days of usual eating and two days at about 500 calories.
  • A fasting-mimicking diet: several days of roughly 800–1,000 calories, designed to keep insulin and protein intake relatively low.

Fung says these approaches may be easier to tolerate while retaining some benefits of fasting. This is his interpretation of the research, not a guarantee of equivalent results.

• Make fasting manageable. Fung describes tea, bone broth, and small amounts of foods such as olives, avocado, or some nuts as “fasting aids” or “training wheels.” He argues that making a fast less difficult may help people continue it, though these foods mean it is not a strict water-only fast.

• Be mindful of what you consume during a modified fast. Fung emphasizes limiting carbohydrates and protein to avoid raising insulin and activating nutrient-sensing pathways such as mTOR. He mentions avocado, olives, some nuts, and bone broth as examples. He also notes that bone broth provides fluid and sodium, along with some protein and minerals.

• Choose a duration that matches the approach and your capacity. The speakers discuss studies of a seven-day water fast and changes that reportedly became more evident after about the third day. Fung suggests that modified fasting may require a longer period than water-only fasting to produce similar effects. These are interview claims, not individualized recommendations. Extended fasting can carry risks and should not be undertaken without appropriate medical advice.

• Focus on sustainable habits, not endurance. Fung’s practical point is that a fasting routine should not feel so punishing that it becomes impossible to repeat. He describes fasting aids as a way to reduce hardship and make the process more sustainable.

• Prioritize real food when ending a fast. The speakers recommend minimally processed foods and discuss meals containing fiber, protein, and healthy fats. They suggest avoiding ultra-processed foods and not letting high-carbohydrate foods crowd out essential nutrients.

• Pair nutrition with muscle use. Fung argues that exercise and muscle use—not simply eating protein—are central to building muscle. He says fasting does not usually cause muscle loss in people with adequate reserves, while acknowledging that fasting could be inappropriate for someone with extremely low body fat. These claims should not replace personalized medical or training advice.

• Visceral fat and metabolic health: Fung distinguishes visceral fat around organs from fat under the skin. He argues that fasting and low-carbohydrate diets can reduce liver fat and visceral fat by lowering glucose and insulin. The conversation presents this as an explanation of metabolic effects rather than a personalized treatment plan.

• Fasting and cancer: Fung discusses fasting as a possible adjunct to cancer treatment, based on theories about insulin and cancer-cell metabolism. He explicitly says fasting should not replace chemotherapy or other prescribed treatment. Anyone with cancer should discuss dietary changes or fasting with their oncology team.

Presenters and sources mentioned

• Presenters: Dr. Jason Fung and Dr. Mindy Pelz.
• Books: The Complete Guide to Fasting and The Obesity Code by Fung; The Hunger Code is referenced in the video context.
• People and organizations: Michael Mosley (5:2 diet); Dr. Walter Longo (fasting-mimicking diet); the American Heart Association (a fasting-related claim attributed to it is criticized by Fung).
• Research discussed: A seven-day water-fasting study described as published in Nature or Nature Medicine, along with studies on modified fasting and “hunger snacking.” The subtitles do not provide full citations.
• Product discussed: A bone-broth powder from AEIRA, promoted during the conversation.