Are Liquids Allowed in Intermittent Fasting?

December 31, 2025 •

4 min read

While intermittent fasting is known for its food-restriction windows, the rules around liquid consumption are often misunderstood. It's a common misconception that all liquids are forbidden, but staying hydrated with the right zero-calorie beverages is not only allowed but highly encouraged to maintain your fast effectively.

Quick Summary

Yes, some zero-calorie liquids are allowed and crucial for hydration during intermittent fasting. Water, unsweetened tea, and black coffee are safe, while drinks with calories, sugar, or artificial sweeteners will break your fast.

Key Points

Zero Calories Are Key: During your fasting window, only consume beverages with zero or near-zero calories to maintain a fasted state.
Stay Hydrated with Water: Water is the most important liquid for intermittent fasting, as it helps with hydration and curbing hunger.
Black Coffee is Allowed: Unsweetened, black coffee can be consumed during fasting, potentially helping with appetite suppression and energy.
Avoid Sugary and Milky Drinks: Beverages with added sugar, milk, or cream will break your fast by triggering an insulin response.
Watch for Artificial Sweeteners: Some artificial sweeteners may affect insulin levels or increase cravings, so they are best avoided during a strict fast.
Replenish Electrolytes: For longer fasts, consider adding a pinch of salt or using a zero-calorie electrolyte supplement to prevent mineral imbalance.
Listen to Your Body: Pay attention to how different liquids affect you, as some may cause digestive issues or increase hunger.
Save Caloric Drinks for Eating Window: Reserve all caloric beverages, including juices, alcohol, and smoothies, for your eating window.

What is a True Fast?

Before exploring specific liquids, it's essential to understand the metabolic state of fasting. During this period, your body shifts from using glucose (sugar) as its primary energy source to burning stored fat, a process known as metabolic switching. The primary goal is to keep insulin levels low, as any significant calorie intake—especially from carbohydrates—will trigger an insulin response and pull you out of the fasted state. For this reason, the golden rule is to stick to liquids with zero or near-zero calories during your fasting window.

The Importance of Hydration

Staying hydrated is a cornerstone of a healthy lifestyle, and this is even more critical during intermittent fasting. When you don't consume food, you miss out on the water content found in fruits, vegetables, and other meals. This makes it essential to actively replenish fluids to avoid dehydration, which can lead to headaches, fatigue, and other unwanted side effects. Water also helps curb hunger pangs and supports the body's natural detoxification processes.

Allowed Liquids During Your Fasting Window

To ensure you reap the full benefits of your fast without breaking it, focus on these zero-calorie beverage options:

Plain Water: This is your best friend during a fast. Drink still or sparkling water throughout the day to stay hydrated.
Black Coffee: Unsweetened, black coffee is permissible and can even be beneficial. Caffeine may help suppress appetite and boost your metabolism. However, avoid adding sugar, milk, or cream, which contain calories and will break your fast. If you have a sensitive stomach, be mindful of your intake.
Unsweetened Tea: Herbal, green, and black teas are excellent, calorie-free options. Green tea is particularly rich in antioxidants. Just like with coffee, avoid any additions like sugar or honey.
Herbal Tea: Caffeine-free herbal teas like chamomile or peppermint are a soothing choice and won't interfere with your fast.
Lemon Water (in moderation): A small squeeze of fresh lemon juice in your water adds flavor with a negligible amount of calories. It’s generally considered fast-friendly, though purists might avoid it.
Diluted Apple Cider Vinegar (ACV): Mixing a teaspoon or two of ACV with water can help with cravings and digestion, without breaking your fast.

Liquids to Avoid While Fasting

Consuming these liquids will trigger an insulin response and effectively end your fast:

Sodas and Sugary Drinks: Regular and diet sodas, fruit juices, and sports drinks are loaded with sugar and calories. Even diet versions with artificial sweeteners can sometimes trigger an insulin response in sensitive individuals.
Milk and Creamers: Any form of milk—dairy or plant-based (almond, oat, soy)—contains carbohydrates and protein that will break a fast. This includes adding even a small splash to your coffee or tea.
Bulletproof Coffee: This popular keto-friendly drink, made with butter and MCT oil, contains a significant amount of calories. While it won't spike insulin as much as sugar, it still provides energy that takes you out of a fasted state.
Alcohol: Alcoholic beverages contain calories and interfere with the fat-burning process, so they are off-limits during your fasting window.
Sweetened Broths: While plain bone broth is often debated but allowed in moderation for longer fasts, store-bought broths can contain hidden calories or sugar. For strict fasting, it's best to stick to water or unsweetened alternatives.

Comparison of Fasting-Friendly and Non-Friendly Beverages


Beverage	Fasting-Friendly?	Why?	Best for...
Plain Water	✅ Yes	Zero calories; essential for hydration.	General hydration and overall health
Black Coffee	✅ Yes	Minimal calories; appetite suppressant.	Energy boost and hunger control
Unsweetened Tea	✅ Yes	Zero calories; provides antioxidants.	Antioxidant intake and variety
Lemon Water	✅ Yes (in moderation)	Negligible calories from a small squeeze of lemon.	Flavor enhancement and vitamin C
Bone Broth	⚠️ Depends on Goal	Low calories, but contains protein; may break a strict fast.	Extended fasts to replenish electrolytes
Diet Soda	❌ No	Artificial sweeteners may trigger insulin or cravings.	Reserved for eating windows
Coffee with Cream	❌ No	Adds calories from fat and sugar.	Eating window consumption
Fruit Juice	❌ No	High in sugar and calories, spikes insulin.	Eating window consumption
Alcohol	❌ No	High in calories, disrupts metabolic processes.	Best avoided, especially while fasting

Potential Issues and How to Address Them

While adhering to the liquid rules is relatively straightforward, some common issues can arise. One is an electrolyte imbalance, especially during longer fasts, where the body loses minerals like sodium and potassium. To combat this, you can add a pinch of high-quality salt to your water or use a zero-calorie electrolyte supplement.

Another challenge is the mental hurdle of giving up sweetened drinks. For those who can't stomach black coffee or plain tea, gradual adjustments or a small amount of a zero-calorie sweetener like stevia or monk fruit are options, though some purists avoid them entirely. Listening to your body is key; if a specific liquid seems to trigger cravings or digestive discomfort, it's best to avoid it.

Conclusion

The question of whether liquids are allowed in intermittent fasting has a clear answer: yes, but with strict conditions. To maintain a true fasted state and reap benefits like weight loss and improved metabolic health, your liquids must be calorie-free. Water, black coffee, and unsweetened teas are your best options for staying hydrated and managing hunger during your fasting window. By being mindful of ingredients and avoiding sugary, milky, or artificially sweetened drinks, you can successfully navigate your fasting periods while keeping your body on track for its health goals.

Frequently Asked Questions

No, black coffee typically does not break a fast as it contains a negligible number of calories and does not significantly impact blood sugar or insulin levels. However, adding sugar, milk, or cream will break the fast.

It is generally not recommended to drink diet soda during intermittent fasting. While zero-calorie, the artificial sweeteners can still trigger an insulin response in some individuals or increase cravings, which can negate the benefits of fasting.

Yes, a small squeeze of lemon juice in water is generally acceptable during intermittent fasting as the calorie count is minimal. However, to stay on the safest side for a 'clean fast,' some prefer plain water only.

Zero-calorie electrolyte supplements will not break a fast and can be beneficial during longer fasting periods to prevent mineral imbalance and side effects like dizziness and fatigue. Sugary electrolyte drinks, however, will break the fast.

No, bulletproof coffee breaks a traditional fast because it contains calories from fats like butter and MCT oil. While it won't spike insulin as much as sugar, the calorie intake still ends the fasted state.

The best liquid to drink while fasting is plain water. It is calorie-free, essential for hydration, and helps with appetite control without affecting your fast.

This is a debated topic. Bone broth contains some protein and calories, which technically breaks a fast. However, some who perform longer fasts use it in moderation to replenish electrolytes, as it has a minimal impact on blood sugar. For a strict fast, it should be avoided.

No, sparkling water does not break a fast as long as it is unsweetened and without any added calories. It can be a refreshing alternative to plain water and may help with feelings of fullness.