You feel thirsty while fasting primarily because your body's water reserves are being depleted, especially as you move deeper into the fast.
Here's a more detailed explanation:
During a fast, your body undergoes several metabolic changes that can contribute to increased thirst:
- Glycogen Depletion: Early in a fast, your body uses stored glycogen (a form of glucose).
- The reference states that "early in a fast, as you burn through glycogen, you'll actually release water into your bloodstream."
- However, this effect is temporary.
- Water Release Slows/Stops: According to the reference, "after your glycogen stores are depleted, deeper into your fast, your body won't have those stores of carbs and water to fall back on, so extra hydration becomes increasingly important." In other words, once glycogen stores are used, your body won't have its carbohydrate/water reserve to help with hydration.
- Electrolyte Imbalance: Fasting can lead to electrolyte imbalances (such as sodium, potassium, and magnesium). These imbalances can disrupt fluid balance, increasing thirst.
- Kidney Function: Your kidneys work to maintain fluid balance. During fasting, they might excrete more fluids to eliminate waste products, potentially leading to dehydration and thirst.
Therefore, staying well-hydrated is crucial throughout the fasting period to counteract these effects and maintain overall health.
