Most rapid scale loss over a 5-day near-zero-calorie fast is water and glycogen, not pure fat. As glycogen drops, water is excreted, so the scale can fall by several kilograms—some of which returns upon refeeding. Five-day fasting can increase risks (dizziness, low blood pressure, electrolyte imbalance, headache/reflux flares, gallbladder issues, binge eating). For weight loss, a safer alternative is an overnight 12–14-hour fast plus a moderate daily deficit with protein- and fiber-rich foods. Longer fasts are higher-risk in diabetes, kidney/heart disease, pregnancy/breastfeeding, and eating-disorder history without medical supervision.