Nutrition Diet: What drinks won't break a fast during intermittent fasting?

October 5, 2025 •

5 min read

According to research published in the New England Journal of Medicine, intermittent fasting provides metabolic benefits like improved glucose control and reduced inflammation. A key to unlocking these benefits is understanding what drinks won't break a fast during intermittent fasting, as consuming the wrong beverage can halt the fasted state and diminish potential health improvements.

Quick Summary

This article explores which beverages are safe to consume during intermittent fasting, differentiating between a strict "clean" fast and a modified approach. Key options include plain water, unsweetened coffee and tea, while milk, sugar, and most zero-calorie sweeteners should be avoided to prevent a metabolic response.

Key Points

Core Principle: A fast is broken by consuming anything with calories, especially carbohydrates and protein, which triggers an insulin response and halts the fat-burning state.
Safe Beverages: Plain water, black coffee, and unsweetened tea are the safest bets for all types of intermittent fasting, as they contain negligible calories.
Modified Fasting: Some fasting approaches allow for very low-calorie drinks like diluted apple cider vinegar or bone broth, which can help with cravings and electrolyte balance.
Strictly Avoid: Dairy, sugar, syrups, juices, and most sodas will break a fast and should be avoided during fasting windows.
Clean vs. Dirty: A 'clean' fast means zero calories, while a 'dirty' fast allows up to 50 calories. The best choice depends on individual goals and adherence needs.
Stay Hydrated: Consuming plenty of water is vital to prevent dehydration, which can be mistaken for hunger, and a pinch of salt can help with electrolyte balance.

The Fundamental Rules of Fasting Beverages

Intermittent fasting works by leveraging the body's metabolic switch, moving from burning glucose for energy to burning stored fat (ketosis) after a period without food. The core principle of a successful fast, especially for strict practitioners, is to avoid anything that triggers an insulin response. Insulin is a hormone that regulates blood sugar, and its release is prompted by the consumption of calories, especially from carbohydrates and protein. Therefore, to maintain a fasted state, the primary rule is to stick to calorie-free or very low-calorie beverages.

The 'Clean Fast' vs. 'Dirty Fast' Debate

When it comes to beverages, fasters often fall into one of two camps: 'clean' or 'dirty'. A clean fast is the most traditional and strictest approach, allowing only plain water, black coffee, and unsweetened tea. The goal is to ingest absolutely no calories to maximize metabolic benefits, particularly the cellular repair process known as autophagy.

A dirty fast, on the other hand, is a more flexible approach that permits a small number of calories during the fasting window, often cited as under 50 calories. This may include a splash of cream in coffee or some bone broth. While this breaks a 'clean' fast, some people find it helps with adherence, especially during longer fasting periods, without completely negating the fat-burning state. The right approach depends on your specific goals and what you can sustainably maintain.

The Best Drinks for Intermittent Fasting

For those adhering to a clean or modified fast, several options are available to keep you hydrated and satisfied without compromising your progress.

Plain Water: The cornerstone of hydration. Still or sparkling water is calorie-free and essential for proper bodily functions, electrolyte balance, and managing hunger pangs during a fast.
Black Coffee: For many, this is a non-negotiable part of their morning routine. Black coffee contains a negligible 3-5 calories per cup and can act as an appetite suppressant, making it easier to extend your fasting window. The key is to consume it without any added milk, cream, sugar, or sweeteners.
Plain Tea: A fantastic alternative or complement to coffee. Plain green, black, white, oolong, or herbal teas are generally low in calories and rich in antioxidants. Varieties like peppermint or ginger tea can also aid digestion and provide a calming effect without breaking your fast.
Diluted Apple Cider Vinegar (ACV): Adding 1-2 tablespoons of ACV to a large glass of water can help curb hunger and potentially improve blood sugar regulation. At about 3 calories per tablespoon, it is acceptable for most modified fasts and does not trigger an insulin response. Remember to dilute it to protect tooth enamel.
Bone Broth: This is where the clean vs. dirty fast distinction is most relevant. Bone broth contains calories (approx. 20-60 per cup), so it will break a strict clean fast. However, for those on a modified fast, it can be a valuable source of electrolytes, collagen, and nutrients, aiding satiety and gut health without a significant insulin spike.

Comparison of Fasting-Friendly Drinks


Drink	Calorie Content	Impact on Insulin	Best For	Considerations
Plain Water	0 kcal	None	All fasting types	Essential for hydration
Black Coffee	3-5 kcal/cup	None	All fasting types	Can suppress appetite; avoid additives
Unsweetened Tea	~2-3 kcal/cup	None	All fasting types	Antioxidants; various flavor options
Diluted ACV	~3 kcal/tbsp	None	Modified fasts	Curbs cravings; dilute to protect teeth
Bone Broth	20-60 kcal/cup	Minimal	Modified fasts	Good for electrolytes, technically breaks clean fast

What to Avoid While Intermittent Fasting

To ensure your fast remains effective, it's equally important to know which drinks will end your fasted state prematurely.

Sugary Drinks: Sodas, fruit juices, and sweetened iced teas are packed with sugar, causing a rapid insulin spike that will immediately break your fast.
Milk and Cream: Even a small splash of dairy or plant-based milk contains calories from fat and carbohydrates. This triggers digestion and a metabolic response, effectively ending your fast.
Added Sugars and Sweeteners: Honey, maple syrup, and any caloric sweeteners should be avoided in all fasting beverages. These will raise blood glucose and insulin levels.
Zero-Calorie Sweeteners: The use of artificial sweeteners like aspartame or sucralose is controversial during a fast. While they don't contain calories, some studies suggest they may still cause an insulin response or affect the gut microbiome. For a strict fast, it's best to avoid them entirely.
Caloric Flavorings: Products like flavored sparkling waters with added sugar or certain pre-packaged tea mixes contain hidden calories that can break a fast. Always check the nutrition label.

Practical Tips for Success

Adhering to your fasting plan is easier with a few simple strategies:

Stay Hydrated: Drink plenty of water throughout the day. Dehydration can be mistaken for hunger, so having a water bottle on hand is crucial.
Brew Your Own: To avoid hidden sugars, brew your own coffee and tea. This gives you complete control over what you're consuming.
Electrolyte Balance: During longer fasts, replenishing electrolytes is vital. A pinch of salt in your water can help maintain mineral balance and prevent fatigue.
Listen to Your Body: If a strict clean fast is causing headaches or intense cravings, a modified fast might be a more sustainable option. What works for one person may not work for another.
Time Your Caffeinated Drinks: If caffeine makes you anxious or disrupts your sleep, time your coffee and tea intake earlier in the day to avoid unwanted side effects.

Conclusion

Ultimately, understanding what drinks won't break a fast during intermittent fasting is key to a successful experience. The safest and most widely accepted beverages are plain water, black coffee, and unsweetened tea. For those who can tolerate it without negative effects, diluted apple cider vinegar offers potential benefits with minimal caloric impact. Bone broth can be a useful tool for modified fasters, but it's important to recognize that it does contain calories. By choosing your drinks wisely, you can stay hydrated and energized while allowing your body to maximize the metabolic benefits of your fasting regimen. For more information on the health benefits of fasting, consider exploring reputable resources like Johns Hopkins Medicine.

Frequently Asked Questions

The use of diet sodas is debated among fasting experts. While they are calorie-free, some experts believe artificial sweeteners can trigger an insulin response or increase cravings for sugar. For a strict 'clean' fast, it is best to avoid them.

Adding a small slice or squeeze of fresh lemon to water is generally considered acceptable and will not break a fast. The caloric content is minimal and unlikely to trigger an insulin response.

Bone broth contains calories (20-60 kcal per cup) and will technically break a clean fast. However, it can be used during a modified fast to provide nutrients and electrolytes, helping with satiety, and is less disruptive than sugary drinks.

Yes, even a small amount of milk or cream, whether dairy or plant-based, contains calories from carbohydrates and fat. This will trigger a metabolic response and break your fast.

Yes, plain herbal teas are generally safe. As long as they are brewed without added sugars or caloric additives, they are typically calorie-free and can provide hydration and flavor.

Yes, diluted apple cider vinegar is often used during fasting. A tablespoon contains only a few calories and is not enough to significantly impact your fasted state. It can also help with managing cravings.

For a strict 'clean' fast, zero calories is the rule. For a modified approach, some individuals aim for a threshold of under 50 calories, but this will break a pure fast and the effects can vary by individual and fasting goals.