What Won't Break My Fast? A Comprehensive Guide

According to a study published in the New England Journal of Medicine, intermittent fasting can lead to a longer lifespan, a leaner body, and a sharper mind. For those exploring this popular health trend, knowing what won't break my fast is crucial to reaping its full benefits. This guide provides a clear overview of the beverages and low-calorie items you can safely consume during your fasting window.

Quick Summary

This guide details the liquids and low-calorie consumables that are safe to have during a fast, distinguishing between strict and modified protocols. It explains why items like black coffee, plain tea, and water are acceptable while outlining additives to avoid for maintaining a fasted state.

Key Points

• Zero-Calorie Liquids: Water, black coffee, and unsweetened tea are generally safe and won't break your fast, as they don't significantly affect insulin levels.

• Mind the Additives: Avoid adding milk, sugar, creamer, or high-calorie sweeteners to your drinks, as these will trigger an insulin response and break your fast.

• Modified Fasting Options: For less strict protocols, small amounts of healthy fats like MCT oil or bone broth can curb hunger without a major insulin spike, though they technically add calories.

• Stay Hydrated: Drinking plenty of water is crucial during fasting to prevent dehydration, which can cause headaches and fatigue.

• Listen to Your Body: Pay attention to how different items affect you. What works for some may not work for others, so adjust your approach based on your own experience.

• Artificial Sweeteners: While zero-calorie, their effect on gut health and appetite is debated, so some fasters choose to avoid them to maintain a strict fast.

The Fundamental Rule of Fasting: The Insulin Response

The core principle behind most intermittent fasting protocols is managing insulin levels. When you eat or drink calories, especially carbohydrates and protein, your body releases insulin to shuttle the glucose into your cells for energy. This process shifts your body out of its fat-burning, fasted state. Therefore, the key to a successful fast is to consume items that have a minimal to zero impact on your insulin levels.

Fasting-Friendly Beverages

Staying hydrated is vital during any fast. Fortunately, many zero-calorie beverages are perfectly acceptable and can help curb hunger pangs.

• Water: Plain water, sparkling water, and mineral water are all excellent choices. They contain zero calories and are essential for hydration, which can help stave off hunger and prevent dehydration symptoms like headaches and fatigue.
• Black Coffee: Unsweetened, plain black coffee is generally considered safe for fasting. A standard cup contains fewer than five calories, which is typically not enough to trigger a significant metabolic response. The caffeine can also help suppress appetite and boost metabolism. However, any added milk, sugar, or high-calorie creamers will break your fast.
• Plain Tea: Similar to black coffee, plain black, green, or herbal teas without any added sugar, honey, or milk are acceptable. Green tea is particularly noted for containing catechins and polyphenols, which some studies suggest can further enhance fasting benefits. Chamomile and peppermint teas are great caffeine-free options.
• Diluted Apple Cider Vinegar (ACV): Some people mix 1–2 teaspoons of ACV with water to aid with hydration and control cravings. The acidity is also known to have a positive impact on blood sugar levels.
• Zero-Calorie Flavorings: A small squeeze of lemon juice in water is permissible, as its calorie count is negligible. Similarly, zero-calorie sweeteners like stevia and monk fruit are generally accepted by most fasting communities, though some purists avoid them as the taste of sweetness can potentially trigger a hormonal response.

The 'Dirty Fast': Navigating Low-Calorie Consumables

Some individuals practice a more lenient form of fasting, sometimes called a "dirty fast," which permits a small number of calories from specific sources. The goal here is to consume a small amount of non-insulinogenic calories (primarily fats) to help extend the fasting window without causing a significant insulin spike.

• Bulletproof Coffee: This involves adding a small amount of healthy fat, such as MCT oil, butter, or coconut oil, to black coffee. While this technically adds calories and breaks a "true" fast, it doesn't significantly spike insulin, keeping the body in a state of ketosis. It's a popular strategy for curbing hunger during a longer fasting period.
• Bone Broth: Bone broth provides electrolytes and nutrients for longer fasts without introducing a large number of calories. A cup or two is acceptable for many fasters and can help alleviate symptoms of electrolyte deficiencies.

The Golden Rule: Listen to Your Body

While guidelines exist, fasting is a personal journey. Pay close attention to how your body responds to what you consume. If a certain item, even a zero-calorie one, makes you feel hungry or unwell, it may be best to avoid it during your fasting window. The long-term health benefits of consistent fasting are more important than rigid adherence to a strict set of rules. Always prioritize safety and consult with a healthcare professional before starting any new dietary regimen, especially if you have underlying health conditions.

Fasting Dos and Don'ts: A Comparison

Item	What is it?	Impact on Fast	Recommendation
Black Coffee	Brewed coffee without milk, sugar, or cream.	Minimal to zero effect on insulin and fat-burning.	Do consume. It can suppress appetite and boost metabolism.
Tea	Plain green, black, or herbal tea.	No significant impact on a fast if unsweetened.	Do consume. Can provide antioxidants and help with hydration.
Water	Plain, sparkling, or mineral water.	Zero effect. Crucial for hydration.	Do consume. Drink ample amounts throughout your fast.
Bulletproof Coffee	Coffee with added MCT oil, butter, or coconut oil.	Technically breaks a strict fast due to calories, but keeps insulin low.	Do consume in moderation for a dirty fast, especially for appetite control.
Diet Soda	Artificially sweetened beverages with zero calories.	Zero calories, but artificial sweeteners may affect some individuals' gut or insulin.	Use with caution, as it's not the healthiest choice.
Regular Soda	Any soda containing sugar.	High in sugar and calories; causes insulin spike.	Do not consume. Will break your fast immediately.
Fruit Juice	Juice from fruit, even if '100% natural'.	High in natural sugars; will break your fast.	Do not consume.
Milk/Creamer	Any form of milk, dairy or non-dairy.	Contains calories, carbs, and sugars (lactose), triggering an insulin response.	Do not consume.
Protein Powders	Supplement mixes containing protein.	High in calories and protein, which activate growth pathways and trigger insulin.	Do not consume.
Chewing Gum	Sugar-free gum or mints.	While low-calorie, the sweet taste and chewing action can trigger a digestive response in some.	Best to avoid if aiming for a strict fast.

Conclusion

Navigating the fasting window is straightforward once you understand the basic principle of avoiding anything that raises your insulin levels. For most, this means sticking to plain water, black coffee, and unsweetened tea. For those on a modified fast aiming for weight loss or metabolic health, small amounts of healthy fats and bone broth may be acceptable. The key to long-term success lies in understanding your own body's response and staying consistent with a protocol that feels sustainable and healthy for you. Always prioritize hydration and listen to your body's signals to ensure a safe and effective fasting experience. Ultimately, the best fasting plan is one that you can maintain over time to achieve your personal health goals. For further guidance on healthy eating, consider visiting a reputable health source like Johns Hopkins Medicine to learn more about nutrition during your eating windows.

Sources

• Johns Hopkins Medicine. (n.d.). Intermittent Fasting: What is it, and how does it work?. Retrieved from https://www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work
• ZOE. (2025, May 7). Intermittent Fasting: What Can You Eat or Drink?. Retrieved from https://zoe.com/learn/what-to-eat-or-drink-while-intermittent-fasting
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Frequently Asked Questions

Can I drink coffee while fasting?

Yes, plain black coffee is acceptable during fasting as it contains very few calories and does not significantly impact insulin levels. Adding sugar, milk, or cream, however, will break your fast.

Does sparkling water break a fast?

No, sparkling water does not break a fast. Like plain water, it contains no calories or macronutrients. However, be cautious of flavored varieties that might contain added sugars.

Are artificial sweeteners okay during fasting?

Zero-calorie sweeteners like stevia and monk fruit are generally accepted by many fasters, as they do not contain calories. Some purists, however, avoid them, as the sweet taste might theoretically trigger a mild hormonal response or cravings.

Does chewing gum break a fast?

Sugar-free gum technically contains minimal calories, but the act of chewing and the artificial sweeteners can trigger a digestive response in some individuals, so it is often best to avoid it for a strict fast.

Can I have bone broth during a fast?

Yes, bone broth is often used in modified or "dirty" fasting protocols. It contains electrolytes and nutrients that can help with longer fasts and curb hunger, without causing a significant insulin spike.

What about lemon juice in water?

Adding a small amount of lemon juice to water is acceptable. The calorie content is negligible and is not enough to break a fast.

Will a protein shake break a fast?

Yes, any protein powder or shake will break a fast. Protein contains calories and amino acids that activate growth pathways and trigger insulin release, shifting your body out of the fasted state.