Fasting involves abstaining from food for a set duration. Hydration is the single most important component of any fast. When the body is not receiving fluids and electrolytes from food, the standard rules for water intake change dramatically. Maintaining fluid balance is absolutely necessary for basic bodily functions and to safely continue a fasting period.
Calculating Water Intake During a Fast
The body requires significantly more water during a fast because it loses fluid it would normally conserve. This increased loss is largely due to the initial depletion of glycogen stores (carbohydrates stored in the muscles and liver). Since glycogen holds about three grams of water per gram stored, releasing it causes a rapid flush of water from the system, leading to increased urination early in the fast.
Food consumption typically provides roughly 20 percent of daily fluid intake. When fasting, this source is eliminated, meaning all fluid requirements must be met solely through beverages. A good baseline recommendation for a healthy adult is approximately 30–35 milliliters per kilogram of body weight.
For example, a 70-kilogram person should aim for around 2.1 to 2.45 liters of water daily. This baseline must be adjusted upward based on personal factors and environmental conditions. Individuals who exercise or live in hot, humid climates must increase fluid intake to compensate for greater losses through sweat. Monitoring the color of urine, which should be a pale yellow, serves as a simple indicator of adequate hydration.
Electrolyte Management for Fasting Hydration
While consuming enough water is necessary, water alone is not sufficient to maintain fluid balance, especially during fasts lasting longer than 24 hours. Electrolytes are minerals essential for nerve signaling, muscle function, and maintaining the correct distribution of water inside and outside cells. Fasting inherently leads to a loss of these minerals due to the absence of food-based intake and increased excretion through urine.
Sodium is a primary electrolyte lost because the kidneys excrete more of it during a fast, often accompanied by more water loss. Low sodium levels can result in symptoms like headaches, dizziness, and muscle cramps. Replenishing sodium is simple and can be accomplished by adding a small pinch of salt, such as sea salt or Himalayan salt, to water throughout the day.
Potassium and magnesium are also depleted, and both are needed for proper muscle contraction and heart rhythm. Magnesium is often helpful in preventing muscle cramps that can occur during a fast. Since these minerals are no longer supplied by food, they must be supplemented, either through a calorie-free electrolyte mix or by dissolving mineral salts in water. Using pure, calorie-free electrolyte sources supports the body’s mineral needs without breaking the fast.
Other Fasting-Friendly Beverages
Several other beverages can be consumed during a fast without disrupting the metabolic state. Black coffee is widely accepted and often encouraged, as it contains no calories and may help with alertness. Plain, unsweetened tea, including both caffeinated and herbal varieties, is also permissible.
Neither coffee nor tea should contain additions like milk, cream, sugar, or caloric sweeteners. Sparkling water and seltzer are excellent calorie-free alternatives to plain water. Some flexibility exists for minimal additions, such as a slice of lemon or lime, which are generally considered acceptable for most fasters. However, beverages that include high-calorie ingredients, such as bone broth or juice, should be avoided.