Fasting's hidden benefits: cellular cleanup, immunity and aging
September 27, 2026 · 20 min read
Chris Palmer on mitophagy, Roger Seheult on immune renewal, David Sinclair on eating less, and Jason Fung all argue that fasting's value goes beyond weight loss to repair and renewal processes. This reframes fasting as a tool for healthspan even for people who aren't trying to lose weight.
The rules, numbers and steps worth keeping in front of you.
- Core idea: fasting's main value is cellular repair and renewal, not weight loss. Weight loss is a side effect.
- Palmer: fasting, calorie restriction and fasting-mimicking diets strongly stimulate autophagy and mitophagy, targeting old and defective parts first.
- Palmer: the ketogenic diet was designed to mimic fasting long term. Early on, 50% of epilepsy patients became seizure-free and another 35% had at least a 50% reduction in seizures.
- Sinclair: low insulin switches on the sirtuins, seven longevity genes. Constant eating keeps them off.
- Sinclair: skipping a single meal can activate longevity pathways. Fasts of about two to three days may trigger deeper chaperone-mediated autophagy.
- Sinclair: skip one meal a day, attached to overnight sleep. Expect the first two to three weeks to be hard, and ease in.
- Fung: people went from three meals a day in the 1970s to five or six eating events today, which keeps insulin high and the body in growth mode.
- Fung: metabolic rate rises 10% after four days of fasting. Hunger comes in waves and often fades after two to three days.
- Seheult: there is good data, including from USC, that intermittent fasting rebuilds the immune system.
- Warning (Fung, Seheult, Sinclair): megadose vitamins and antioxidants are no substitute for fasting. Beta-carotene raised cancer risk, and high-dose vitamins E and A hastened deaths in lung cancer patients.
- Warning: much of the longevity evidence comes from animals, and lab results often fail in living people (Seheult).
- See a physician before fasting longer than a day if you have diabetes, an eating disorder history, pregnancy, a chronic illness or take medications. Never stop psychiatric medication without your prescriber (Palmer).
This is the short form. The full insight has every expert's reasoning, their own words and the sources.