Is drinking liquids considered breaking a fast? An essential guide to hydration and nutrition

October 19, 2025 •

4 min read

Over half of American adults have tried some form of intermittent fasting, according to Johns Hopkins Medicine. A frequent point of confusion for those new to the practice is knowing what constitutes breaking a fast, specifically is drinking liquids considered breaking a fast or is it permitted to stay hydrated?

Quick Summary

Whether a liquid breaks a fast depends on its caloric content and individual metabolic response. Plain water, black coffee, and unsweetened tea are generally acceptable, while any beverage with calories or artificial sweeteners can potentially disrupt the fasted metabolic state, depending on your goals.

Key Points

The Bottom Line: Plain water, black coffee, and unsweetened tea will not break a fast as they contain zero or negligible calories.
Know Your Goals: The impact of liquids depends on whether you are doing a 'clean' fast (zero calories) or a 'dirty' fast (minimal calories allowed).
Hidden Culprits: Popular drinks like sodas, juices, and coffee with milk or cream contain calories and will halt the metabolic state of fasting.
Artificial Sweeteners: These can cause a debated insulin response or increase cravings, potentially undermining some fasting benefits, and are best avoided during a clean fast.
Don't Forget Electrolytes: During longer fasts, supplementing with sugar-free electrolytes can prevent side effects like fatigue and headaches caused by mineral loss.
Dry Fasting: A specific and strict method of fasting that involves abstaining from all food and liquids, including water.

The Science of Fasting and Metabolic Switching

Fasting is an eating pattern that cycles between periods of eating and abstaining from food, rather than focusing on what to eat. The physiological goal for many who fast is to prompt a 'metabolic switch'. After several hours without food, the body depletes its stored sugar (glucose) and begins to burn fat for energy, a process known as ketosis.

Central to this process is the hormone insulin. When you eat or drink calories, your body releases insulin to manage blood sugar. During a fast, insulin levels drop significantly, allowing your body to access and burn its stored fat for fuel. Therefore, consuming anything that causes a significant insulin spike will effectively 'break' the fast and halt this beneficial metabolic state. This principle is key to understanding the nuanced rules surrounding liquid intake.

The 'Clean' vs. 'Dirty' Fast

Fasting protocols are often categorized as either 'clean' or 'dirty'.

Clean Fasting: A strict approach where only zero-calorie beverages are consumed during the fasting window. The goal is to avoid any substance that might trigger an insulin response and to maximize processes like autophagy (the body's cellular cleaning process).
Dirty Fasting: A modified approach that allows for a minimal number of calories (often cited as less than 50-100 kcal) from certain liquids or foods. While this might make fasting easier for some, it does technically break the metabolic fast and may compromise some of the deeper benefits.

Liquids That Will NOT Break a Fast

For those adhering to a clean fast, these beverages are safe to consume during fasting periods:

Plain Water: The cornerstone of hydration. Water is calorie-free and essential for bodily functions, helping to prevent dehydration and manage hunger pangs. This includes still, mineral, and sparkling water, as long as they contain no added sweeteners.
Black Coffee: With only 3-5 calories per cup, plain black coffee is generally considered safe. Its caffeine content can help suppress appetite and promote alertness. However, any additions like milk, sugar, or cream will break a fast.
Unsweetened Tea: Green, black, and herbal teas are excellent choices, provided they are unsweetened and without milk. They contain negligible calories and provide antioxidants.
Diluted Apple Cider Vinegar: Some protocols permit 1-2 teaspoons mixed with water. It contains very few calories and may help with hydration and appetite control.
Plain Electrolyte Supplements: For longer fasts, replenishing electrolytes is crucial. Pure, unsweetened electrolyte powders or tablets contain no calories and will not break a fast.

Liquids That WILL Break a Fast

Any beverage that contains calories, carbohydrates, or protein will signal the body to exit the fasted state. These should be avoided during the fasting window:

Sugary Drinks: This includes regular sodas, juices (even freshly squeezed), and sweetened iced teas. Their high sugar content causes a rapid insulin spike.
Milk and Cream: Whether dairy or plant-based, milk contains calories and can trigger an insulin response, breaking a fast.
Coffee with Additives: Lattes, cappuccinos, or coffee with any added sugar, syrups, or cream are not acceptable during a clean fast.
Sports and Energy Drinks: These are typically loaded with sugar and electrolytes, making them off-limits.
Alcohol: The body will prioritize metabolizing alcohol, halting fat-burning processes.
Bone Broth: Contains protein and calories. While nutritious, it will break a strict fast. It's best reserved for the eating window or for specific modified fasting protocols.
Bulletproof Coffee: This popular 'dirty fast' beverage, made with butter or MCT oil, contains calories and stops the deeper fasting benefits, though it may help maintain ketosis.

The Debate: Diet Sodas and Artificial Sweeteners

Diet sodas are a source of controversy in the fasting community. While they contain zero calories, some studies suggest that artificial sweeteners like aspartame and sucralose can have a metabolic effect.

Insulin Response: The sweet taste can sometimes trigger a 'cephalic phase' insulin response, where the body prepares for sugar that never arrives. While the impact is often minimal and varies between individuals, purists avoid them entirely to prevent any potential hormonal disruption.
Gut Health: There is some evidence that artificial sweeteners can negatively impact the gut microbiome, which is not ideal for long-term health.
Cravings: Some fasters find that the sweet taste of diet soda increases their cravings for sugary foods, making it harder to stick to their plan.

Comparison of Fasting Liquids


Beverage Category	Effect on Fast	Best For	Considerations	Source
Plain Water	Safe (Zero Calories)	All fasts, essential for hydration and satiety.	The simplest and best choice for hydration.
Black Coffee / Unsweetened Tea	Safe (Negligible Calories)	Appetite suppression, energy boost, and antioxidants.	Avoid all additives like milk, sugar, or cream.
Diet Soda / Artificial Sweeteners	Debated	Calorie restriction goals.	May trigger an insulin response or increase cravings; avoid for strict metabolic benefits.
Milk / Sugary Drinks	Breaks Fast	Not suitable for fasting periods.	Any drink with significant calories will halt the fasted state.
Bone Broth	Breaks Clean Fast (Contains Calories/Protein)	Modified fasting, or for breaking a fast gently.	Avoid for strict fasts focused on autophagy.

Conclusion

Ultimately, whether drinking a liquid is considered breaking a fast depends on the liquid's content and your specific goals. For a true 'clean' fast focused on maximizing metabolic benefits like ketosis and autophagy, only pure, non-caloric liquids are acceptable. This includes plain water, black coffee, and unsweetened tea. While the effects of artificial sweeteners are debated, most experts recommend avoiding them to prevent potential metabolic disruptions or increased cravings. By understanding the science behind fasting and metabolic switching, you can make informed decisions about your liquid intake to best support your health journey.

For more information on the science of intermittent fasting, consult resources from reputable institutions like Johns Hopkins Medicine.

Frequently Asked Questions

Yes, drinking water is not only allowed but highly recommended during fasting to stay hydrated without adding any calories or affecting your insulin levels.

No, plain black coffee contains only 3-5 calories per cup and does not cause a significant insulin spike, making it generally acceptable during a fast.

The answer is debated. While technically calorie-free, the artificial sweeteners can trigger an insulin response or increase cravings in some individuals, potentially interfering with the metabolic benefits of a fast. For a clean fast, it is best to avoid them.

No, adding milk, cream, or any other calorie-containing additive will break a clean fast by triggering a metabolic response.

Bone broth contains protein and calories, which will break a clean fast. Some modified fasts allow it, but for a strict fast, it should be avoided during fasting periods.

Yes, if they are unsweetened and calorie-free. Electrolytes are often necessary during longer fasts to replace lost minerals and prevent side effects like headaches or muscle cramps.

A clean fast is a strict fast where only zero-calorie beverages are consumed. A dirty fast allows a minimal number of calories, often less than 50-100, during the fasting window, which technically breaks the fast.

If you accidentally consume something with calories, your body will temporarily exit the fasted state. The impact depends on the amount and your specific fasting goals, but you can simply resume your fast and continue as planned.