Can You Drink Water During Intermittent Fasting 16:8?

October 21, 2025 •

3 min read

According to Johns Hopkins Medicine, after hours without food, the body exhausts its sugar stores and begins burning fat, a process known as metabolic switching. Hydration is a critical component of a successful fasting regimen, and many people wonder: can you drink water during intermittent fasting 16:8? The short and simple answer is yes, and it is highly recommended.

Quick Summary

During the 16-hour fasting window of the 16:8 method, consuming water is essential for staying hydrated and supporting the body's metabolic functions. Plain, calorie-free water will not break a fast and can also help manage hunger pangs and reduce the risk of dehydration-related side effects.

Key Points

Yes, water is essential: You can and should drink water during the fasting window of the 16:8 intermittent fasting method.
Water doesn't break a fast: Because water contains no calories, it does not trigger an insulin response or break your fasted state.
Prevent dehydration side effects: Staying hydrated helps prevent common fasting side effects like headaches, dizziness, and fatigue, which are actually symptoms of dehydration.
Manage hunger effectively: Drinking water can help manage hunger pangs by creating a feeling of fullness in your stomach.
Acceptable non-water drinks: Other calorie-free beverages like black coffee and unsweetened tea are also permitted during your fast.
Replenish electrolytes: As the body loses water during a fast, some individuals may benefit from zero-calorie electrolyte supplements to maintain mineral balance.
Maintain metabolic benefits: Proper hydration supports your metabolism and the fat-burning process of metabolic switching.

Why Proper Hydration is Crucial During the Fasting Window

While fasting involves abstaining from calories, drinking water is essential. Fasting causes physiological changes that impact fluid balance. Lower insulin levels lead to increased sodium and water excretion by the kidneys. Glycogen breakdown also releases bound water, further contributing to fluid loss. Therefore, consistent water intake is vital during fasting.

The Science Behind Water and Fasting

Water is calorie-free and does not raise blood sugar or insulin, which is key to maintaining a fasted state in protocols like 16:8. It doesn't interfere with metabolic switching from glucose to fat burning. Proper hydration aids in temperature regulation, joint lubrication, nutrient transport, and waste removal.

The Benefits of Drinking Water During a Fast

Hydration improves the intermittent fasting experience by mitigating common side effects like headaches, dizziness, and fatigue, often caused by dehydration. It can also help manage appetite by creating a feeling of fullness.

What Liquids Can You Have During a 16:8 Fast?

Beyond plain water, several zero-calorie beverages are acceptable during a fast. The rule is to avoid drinks with calories or sugar to prevent an insulin response.

Permitted Calorie-Free Beverages:

Plain Water: Still or sparkling.
Black Coffee: Unsweetened.
Unsweetened Tea: Green, black, or herbal.
Lemon Water: Small amount of fresh lemon.
Electrolyte Water: Zero-calorie versions for mineral replenishment.
Bone Broth: Some use it for nutrients, but it contains calories and is considered a "dirty fast".

Beverages to Strictly Avoid:

Soda and fruit juices
Coffee with added sugar, milk, or cream
Diet sodas and beverages with artificial sweeteners (may affect insulin)
Alcoholic beverages
Flavored water with added sugars or artificial sweeteners

Hydration Guide: Fasting vs. Non-Fasting Periods


Feature	During 16-Hour Fasting Period	During 8-Hour Eating Period
Recommended Intake	Drink plenty of water and other calorie-free liquids, aiming for at least 8-12 cups total.	Continue drinking plenty of water, but a wider range of beverages is permitted.
Key Focus	Staying hydrated and managing hunger with calorie-free liquids to maximize fat-burning benefits.	Replenishing fluids and electrolytes while enjoying a healthy variety of foods and beverages.
Allowed Drinks	Plain water, sparkling water, black coffee, unsweetened tea, lemon water, electrolyte water.	Any drinks, including milk, juice, and smoothies, as long as they fit within your dietary goals.
Benefits	Reduces hunger pangs, supports metabolic switch, prevents dehydration symptoms like headaches.	Optimizes nutrient absorption and energy utilization from food and drinks.

What Happens if You Don't Drink Enough Water?

Insufficient water during fasting can cause headaches, fatigue, dizziness, irritability, and dry mouth—often mistaken for fasting side effects. Severe dehydration can lead to more serious issues. Staying hydrated ensures a more comfortable fast.

Conclusion: Prioritize Water for a Successful Fast

Drinking water during intermittent fasting 16:8 is not only allowed but essential. Proper hydration supports metabolic functions, helps manage hunger, and prevents dehydration-related side effects. Stick to zero-calorie drinks during your fast to maintain metabolic benefits. Always consult a healthcare professional before starting any new dietary plan, especially with existing health conditions. Hydration is key to an effective and comfortable intermittent fasting journey.

For more detailed information on intermittent fasting, explore resources like Johns Hopkins Medicine.

Frequently Asked Questions

Yes, sparkling water is permitted during a 16:8 fast as long as it contains no added sugars, flavors, or calories that could break your fast.

A small amount of fresh lemon squeezed into your water is typically acceptable during a fast. The calories are negligible and won't trigger an insulin response.

There is no one-size-fits-all answer, but many experts recommend aiming for at least 8 to 12 cups throughout the day. It is best to listen to your body and drink whenever you feel thirsty.

During fasting, your body releases stored water as it uses up glycogen reserves and your kidneys excrete more sodium due to lower insulin levels. This increases the risk of dehydration, so more water is needed to compensate.

Signs of dehydration during a fast include headaches, dizziness, dark yellow urine, fatigue, muscle cramps, and a dry mouth.

No, adding milk, cream, or sugar to your coffee will add calories and break your fast. You must stick to black, unsweetened coffee during your fasting period.

Yes, drinking water can help reduce the sensation of hunger by filling your stomach and keeping you feeling fuller for longer. Sometimes what feels like hunger is actually thirst.