What Can I Put in My Coffee While Intermittent Fasting?

January 8, 2026 •

3 min read

According to research, moderate amounts of black coffee are generally accepted during an intermittent fasting window, containing fewer than 5 calories per cup. However, the real question for many enthusiasts is what to put in my coffee while intermittent fasting without sabotaging progress.

Quick Summary

This guide details which additives are safe for intermittent fasting, categorizing options like spices and zero-calorie sweeteners, explaining the impact of fats like MCT oil, and clarifying why sugar and milk should be avoided to maximize fasting benefits.

Key Points

Black Coffee is Safest: Black coffee, containing minimal calories, is the safest and most effective option for a 'clean' intermittent fast without breaking it.
Add Calorie-Free Spices: Use a pinch of cinnamon, nutmeg, or unsweetened cocoa powder to add flavor and depth without adding calories.
Be Wary of Zero-Calorie Sweeteners: While technically calorie-free, sweeteners like stevia and monk fruit are a gray area, as the sweet taste could potentially trigger an insulin response or increase cravings.
Fats Break a Clean Fast: Additions like MCT oil, butter, or coconut oil (Bulletproof coffee) contain calories and will break a clean fast, though some on keto diets use them to prolong satiety.
Avoid Sugars and Dairy: Any form of sugar, milk, cream, or flavored syrup will cause an insulin spike, immediately ending the fasted state.

Understanding the Fasting Rulebook

Intermittent fasting offers potential benefits like weight management and metabolic health. A true fast involves stable insulin levels and avoiding caloric intake that triggers a significant insulin response. This differentiates a “clean” fast (allowing only water, black coffee, or tea) from a “dirty” fast (allowing a small number of calories, typically under 50). The best approach depends on individual fasting goals, with stricter methods favored for benefits like autophagy.

Fasting-Safe Coffee Additions

For those who prefer coffee with flavor but want to maintain a fasted state, several zero-calorie options can enhance taste without breaking the fast.

Spices

A pinch of spices like cinnamon or nutmeg can add warmth and flavor, while a tiny amount of unsweetened cocoa powder offers a chocolatey note. Some research suggests cinnamon may even help regulate blood sugar.

Flavor Extracts

A couple of drops of pure, unsweetened vanilla or peppermint extract can add aroma and flavor without impacting your fast, provided they contain no sugar or alcohol.

Other Additions

A tiny pinch of salt can neutralize bitterness, making black coffee more palatable.

The Gray Area: Zero-Calorie Sweeteners

The impact of zero-calorie sweeteners like stevia, monk fruit, and erythritol during fasting is debated. While calorically safe, some suggest the sweet taste might trigger an insulin response or increase cravings, potentially disrupting the fast. Avoiding all sweeteners may be preferable for those aiming for metabolic processes like autophagy.

The “Dirty Fast” Approach: Fats in Coffee

Bulletproof coffee, containing coffee, butter, and MCT oil, is popular for providing energy and curbing hunger. It provides calories and breaks a clean fast. However, since the calories are from fats, they don't cause a significant insulin spike like carbohydrates. This method suits those prioritizing ketosis and hunger suppression over a strict caloric fast.

Comparison of Coffee Additives

Below is a summary of common coffee additives and their impact on fasting goals.


Additive	Effect on Clean Fast	Best for Keto/Weight Loss?	Calories per serving	Key Consideration
Black Coffee	Safe	Yes	~5	Safest option for maximum benefits.
Spices (Cinnamon, Nutmeg)	Safe	Yes	Negligible	Add flavor without calories.
Zero-Cal Sweeteners (Stevia, Monk Fruit)	Gray Area	Yes (Usually)	0	May trigger insulin in some; risk of cravings.
MCT Oil/Butter	Breaks Fast	Yes (Dirty Fast)	100-200+	Curbs hunger, supports ketosis, but adds calories.
Milk/Cream	Breaks Fast	No	Varies (High)	Contains carbs/lactose that spike insulin.
Sugar/Syrups	Breaks Fast	No	Varies (High)	Direct insulin spike, immediately ends fast.
Collagen/Protein	Breaks Fast	No	Varies (High)	Adds protein and calories that stop fasting state.

Additives That Definitely Break a Fast

To maintain your fast, avoid any additions with significant calories, especially carbohydrates or protein, as they cause an insulin response. This includes sugar and sweetened syrups (like honey and maple syrup), milk and dairy replacements (even a small amount), and collagen or protein powders.

Tips for Transitioning to Black Coffee

Adjusting to black coffee can be easier with a few tips:

Use High-Quality Beans: Better beans offer a more enjoyable flavor.
Try Low-Acid Coffee: This can help if black coffee irritates your stomach.
Go Cold: Cold brew can be smoother and less acidic.
Add a Pinch of Salt: This can counteract bitterness.

Conclusion

What you add to your coffee while intermittent fasting depends on your goals. For a strict "clean fast," black coffee and water are the safest. For weight loss with a less strict approach, spices or zero-calorie sweeteners might be acceptable, although the latter is debated. The "dirty fast" with fats like MCT oil can help suppress hunger during keto fasts but is not suitable for a strict caloric fast. Understanding each additive's impact allows for informed choices that support your fasting journey.

Frequently Asked Questions

Yes, adding any amount of milk, including dairy or plant-based alternatives, adds calories and lactose, which triggers an insulin response and breaks a clean fast.

The consensus is split. While they don't add calories, some studies suggest the sweet taste alone can provoke an insulin response. For a strict 'clean' fast, it's best to avoid them, but for less strict fasts, they are a better option than sugar.

A clean fast permits only water, black coffee, and unflavored tea, while a dirty fast allows a minimal number of calories (usually under 50) during the fasting window.

Yes, because it contains calories from fats like butter and MCT oil, bulletproof coffee technically breaks a clean fast. However, because it doesn't spike insulin significantly, some use it on keto diets to extend their fasting window.

Yes, a pinch of spices like cinnamon or nutmeg is generally considered safe during a fast. They contain negligible calories and can improve the flavor of black coffee.

As long as the flavoring is added during the roasting process and is calorie-free, it's typically fine. Avoid artificially sweetened or high-calorie flavored options.

Try using high-quality beans, brewing cold brew for a smoother taste, or adding a pinch of salt to reduce bitterness. Pure, unsweetened flavor extracts like vanilla are also an option.