Not eating for 5 days can reduce scale weight quickly, but much of the loss is water, glycogen, and gut content. The risk of muscle loss and metabolic adaptation is high. Prolonged fasting without medical supervision may cause dizziness, poor concentration, low blood pressure, gallstone risk, and rebound overeating. This is not a safe fat-loss strategy. For healthier, sustainable fat loss, use a controlled calorie deficit, adequate protein, and a repeatable movement plan.