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Short Summary
Main recommendation: Dr. Jason Fung presents intermittent fasting, meaning periods without eating, as a way to drain excess glucose and burn stored body fat, which he says may help reverse type 2 diabetes. He cites a 2023 study in which he says 47.2% of participants achieved remission and came off their diabetes medications.
Key Points
- Dr. Fung frames type 2 diabetes as a glucose overflow problem: excess sugar spills over, and fasting drains it by letting the body burn it for fuel.
- Fasting lowers insulin, increases fat burning, raises growth hormone to help preserve muscle and bone, and raises sympathetic nervous system activity, which reduces hunger and increases metabolic rate.
- Dr. Fung lists advantages of fasting: 1) it is simple, with no complicated food rules; 2) it is free, and saves money; 3) it is flexible around holidays or vacations; 4) it is convenient, saving time on shopping, cooking, eating, and cleanup; 5) it can be combined with any diet.
- Dr. Fung names three fasting mistakes to avoid: 1) overeating after the fast; 2) letting food triggers, such as the sight, smell, or talk of food or cooking for family, derail you; 3) doing it alone instead of with a supportive group or friends.
Details Worth Noting
- Concrete instructions: Choose a period when you don't eat, and eat as normally as possible afterward without overeating. Progress through fasting schedules: a 12 to 14 hour overnight fast (for example, dinner around 7 p.m. and breakfast between 7 and 9 a.m.) is normal and not strong enough for weight loss; extend to 16 hours by eating earlier (for example, 9 a.m. to 3 p.m.) or later (11 a.m. to 7 p.m.); a 24-hour fast is a one-meal-a-day schedule; for longer fasts, skip one meal across two days (for example, dinner Monday, nothing all of Tuesday, breakfast Wednesday) for a 36-hour fast. Dr. Fung says to be careful with extended fasts if you take medications. Modified fasts with about 200 to 500 calories, usually from vegetables, still provide most benefits and are easier. To manage triggers, have someone else cook or cook ahead and freeze meals. Tell friends or family about your fast so they can support you or join you.
- Dr. Fung says fasting does not burn muscle, citing a 10-day fast study in which leg strength rose and stayed up after fasting ended.
- In a study of breakfast versus skipping breakfast, eating breakfast led to about 260 more calories per day.
- In a four-day fasting study, resting energy expenditure rose about 10%, and oxygen use (VO2) also rose about 10%, suggesting metabolism speeds up rather than slows.
- Hunger from fasting peaks and then falls back to baseline within about two hours of the peak, according to a 24-hour ghrelin study.
- Dr. Fung cites a survey in which about 75% of doctors who lost weight said they used intermittent fasting, yet only about 20 to 30% recommend it to patients.
Bottom Line
Fasting is presented as a simple, free, flexible way to use stored sugar and fat for fuel, with the main practical challenge being avoiding overeating after fasting periods and managing food triggers.
