Prolonged fasting causes the body to undergo time-dependent metabolic changes that can bring both potential effects and serious risks. After around three days, glycogen stores are largely depleted and the body increasingly turns to fat and ketones for energy, often causing headaches, dizziness and poor concentration. By five days, ketosis becomes more pronounced, but water, muscle and electrolyte losses can occur. After seven days, muscle breakdown and reduced endurance may become more significant. Fasting for 10 days or longer increases the risk of dehydration, electrolyte imbalances, heart rhythm problems and dangerous refeeding complications. Experts stress that prolonged fasting should only be undertaken under medical supervision.
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