What it’s for
- Supervised or personal fasting experiments
An extended period without food, usually longer than a day.
Purpose, evidence and practical considerations.
Human studies report short-term weight and metabolic changes. Evidence for durable clinical benefit or longer life is limited, and supervised results cannot establish safety for unsupervised fasting.
Confidence: weak
Risks include dehydration, electrolyte disturbances, loss of lean tissue, hypoglycaemia and problems when refeeding. Pregnancy, eating disorders, frailty and diabetes medicines make unsupervised fasting especially concerning.
Fasting reduces incoming energy and shifts fuel use towards stored fat and ketones. These changes do not themselves establish durable health outcomes.
How people use it, with their schedules, context and original sources.
7–10 days quarterly, or 3 days monthly