The Biology of Fasting: Vetted Science Meets Spiritual Discipline

What a 14-hour fast actually does to the liver, the brain, and the mood — and where the clinical data stops and the practice begins.

• The fast is older than the clinic.
• Twelve to sixteen hours without caloric intake depletes hepatic glycogen.
• That last finding matters for anyone who treats a fast as a devotional practice: the body you bring to the discipline is not the body in the study.