What drink does not break intermittent fasting?

December 24, 2025 •

5 min read

According to Johns Hopkins neuroscientist Mark Mattson, our bodies evolved to go for many hours without food, making intermittent fasting a natural process. Choosing the right beverages during your fasting window is crucial for success, and knowing what drink does not break intermittent fasting is key to reaping the full benefits of this metabolic switch.

Quick Summary

Pure, calorie-free liquids are the safest options for maintaining a fasted state. Water, black coffee, and unsweetened teas are the best choices. Caution should be exercised with diet sodas and flavored beverages, as artificial sweeteners can potentially affect metabolic response and hunger. Adding calories, sugar, or milk will break a fast, ending the metabolic benefits.

Key Points

Zero Calories Are Safe: The fundamental rule is to consume zero-calorie beverages like water, black coffee, and unsweetened tea to stay in a fasted state.
Water is Best: Plain, sparkling, or infused water is the most optimal choice for hydration and will not break your fast under any circumstances.
Unsweetened Coffee & Tea are Acceptable: Black coffee and unsweetened green or herbal tea can be consumed during fasting and may even offer enhanced fat-burning and antioxidant benefits.
Avoid Sugars and Dairy: Drinks containing sugar, milk, or cream will break a fast by triggering an insulin response and should be avoided.
Use Caution with Artificial Sweeteners: The effect of artificial sweeteners on fasting is debated; some may trigger a metabolic response. For stricter fasts, avoiding them is recommended.
Bone Broth is a Modified Fast: While nutrient-dense, bone broth contains calories and is only suitable for modified fasts, not a true zero-calorie fast.

The Core Principle: Zero Calories

At its heart, intermittent fasting is about giving your body a break from processing and digesting food, allowing it to tap into stored fat for energy in a process called ketosis. For this reason, the fundamental rule for what to drink is simple: choose zero-calorie beverages. Any drink with significant caloric content, especially carbohydrates or protein, will trigger an insulin response, effectively breaking your fast. This isn't just about weight loss; for those seeking benefits like improved insulin sensitivity or autophagy (cellular cleanup), maintaining a true fasted state is paramount. The good news is that this doesn't mean you're limited to only plain water. There are several flavorful and hydrating options available.

Fast-Friendly Beverages

The Gold Standard: Water

Water in all its forms—plain, sparkling, or mineral—is the best and safest drink for any intermittent fast. It is calorie-free and essential for hydration, curbing hunger pangs, and helping the body eliminate waste. For those who find plain water boring, adding natural flavorings is a great option. A few drops of lemon or lime juice are generally acceptable, as the caloric impact is negligible and won't significantly affect your fasted state. Infusing water with cucumber or mint is another delicious, zero-calorie way to add flavor. Stay hydrated, especially when your food intake is limited, to prevent fatigue and headaches.

Your Morning Ritual: Black Coffee and Tea

For many, coffee is an indispensable part of the day, and it's perfectly safe during a fast, as long as it's black and unsweetened. The caffeine can provide an energy boost and help suppress appetite, making fasting easier. Similarly, most teas are fast-friendly, provided they are unsweetened. Green tea is a popular choice for its antioxidants, while herbal teas like chamomile or peppermint are excellent caffeine-free options. Just remember, no milk, cream, or sugar should be added, as these will break your fast.

Advanced Fasting Drinks

For those on longer fasts, certain beverages can help with electrolyte balance and gut health without completely disrupting the fast. A small amount of diluted apple cider vinegar (ACV) or bone broth can be incorporated. ACV (1-2 tablespoons diluted in water) is very low in calories and may aid blood sugar control. A small cup of high-quality bone broth contains electrolytes and nutrients that can help with longer fasts, though it does contain a small amount of calories, making it suitable for a less-strict or "dirty" fast. It's crucial to check labels for additives in store-bought versions.

Drinks to Avoid During Fasting

To maintain the benefits of a fasted state, steer clear of these common beverages:

Sugary drinks and juices: This includes regular soda, fruit juice, and sports drinks. They are packed with sugar and calories that will immediately spike your insulin.
Milk and cream: Any dairy product, including milk and cream, contains calories and lactose (a natural sugar), which will trigger an insulin response and break your fast.
Diet sodas and artificial sweeteners: This is a controversial area. While diet sodas contain zero calories, some artificial sweeteners may trigger a cephalic phase insulin response in some individuals, potentially disrupting fasting benefits like autophagy. For those pursuing a strict fast, it's best to avoid them.
Alcohol: All forms of alcohol contain calories and are dehydrating. Drinking on an empty stomach during a fast is especially risky and will break your fast.
Bulletproof Coffee: While popular in keto circles, this coffee with added butter and MCT oil is not a zero-calorie drink and will break a strict fast. It's a method of "dirty fasting" that provides energy from fat but stops deeper fasting processes.

Comparison of Fasting-Friendly and Non-Friendly Drinks


Beverage	Fasting-Friendly?	Calories	Notes
Plain Water	✅	0	The ultimate option for hydration and curbing hunger.
Sparkling Water	✅	0	A good alternative to plain water, with added fizz.
Black Coffee	✅	≈3-5	Provides a caffeine boost and helps suppress appetite. Must be unsweetened.
Unsweetened Tea	✅	≈0-2	Green, black, or herbal teas are excellent choices for hydration and antioxidants.
Apple Cider Vinegar (diluted)	✅	≈3-6	Very low calorie, may help with blood sugar and cravings.
Bone Broth	(Modified Fast)	≈20-60	High in nutrients, but has calories. Best for modified or longer fasts.
Diet Soda	(Controversial)	0	May trigger an insulin response due to artificial sweeteners, potentially affecting deeper fast benefits.
Milk / Cream	❌	Varies	Contains calories and sugar (lactose), triggering an insulin spike.
Fruit Juice	❌	High	High in sugar and calories, will break your fast.
Regular Soda	❌	High	Contains significant calories and sugar, must be avoided.

The "Dirty Fasting" Approach

For some intermittent fasters, especially those primarily focused on weight management, a "dirty fast" allows for a minimal calorie intake during the fasting window, often cited as under 50 or 100 calories. This might mean a splash of milk in coffee or a cup of bone broth. The theory is that it provides a psychological and physiological buffer that helps maintain the fasting routine, without a major metabolic disruption. However, it's important to recognize that this is a modified approach and will technically break a true, calorie-free fast, potentially limiting benefits like autophagy. For purists or those seeking maximum cellular benefits, a clean fast is the only way to be certain.

Conclusion

For most people practicing intermittent fasting, plain water, black coffee, and unsweetened teas are the safest and most reliable beverage choices. They provide hydration and other benefits without risking a break in the fast. More advanced options like diluted apple cider vinegar and bone broth offer additional benefits for those who tolerate them and are following a more modified approach. The key is to be mindful of your goals. If your focus is weight loss, a few calories might not matter, but for maximum metabolic benefits and cellular repair, keeping your liquid intake as calorie-free as possible is the best path forward. Always consult with a healthcare professional before starting any new diet regimen.

For more information on the science of intermittent fasting, consult the research available from institutions like the New England Journal of Medicine, which has published studies on its health benefits.

Frequently Asked Questions

No, adding milk, cream, or any other form of dairy to your coffee adds calories and sugar (lactose), which will break your fast and negate its metabolic benefits.

The answer is debated. While diet sodas are zero-calorie, their artificial sweeteners may trigger an insulin response in some individuals, potentially disrupting certain fasting benefits. For strict fasting, it is best to avoid them.

Yes, a small amount of lemon juice squeezed into your water is generally acceptable. It contains minimal calories and shouldn't significantly impact your fast, while providing a refreshing flavor.

Sugar-free electrolyte supplements will not break a fast and can be very beneficial during longer fasts to maintain proper hydration and mineral balance. Avoid products with added sugars or calories.

Bone broth contains calories and technically breaks a true fast. However, it is often included in modified or "dirty" fasting protocols, especially for longer fasts, due to its nutritional benefits and ability to curb hunger.

"Dirty fasting" is a term used for consuming a small amount of calories, typically under 50-100, during the fasting window. This is a more lenient approach than a traditional zero-calorie fast and may not provide the same cellular-level benefits like autophagy.

No, unsweetened herbal tea is a safe and calorie-free beverage option during a fast. Examples include chamomile, peppermint, and ginger tea, and they can provide variety and additional health benefits.