Does butter in coffee break a fast?

Yes. A tablespoon of butter has about 100 calories of fat, enough to end a clean fast even though it raises insulin very little.

Does bulletproof coffee break ketosis?

No for most people. It is almost pure fat, and MCT oil is turned into ketones quickly.

Is bulletproof coffee good for weight loss?

Only if it replaces a meal you would otherwise eat. Added on top of your usual food, its 200 or more calories work against a deficit.

What can I add to coffee without breaking my fast?

Cinnamon, a pinch of salt, or a zero-calorie sweetener keep black coffee fast-friendly.

Does Bulletproof Coffee Break a Fast? Yes

Reviewed by the FastTrack team · Updated June 2026

Short answer: Yes

Yes, bulletproof coffee breaks a fast in the strict sense. A typical cup with a tablespoon each of butter and MCT oil carries about 200 to 250 calories of fat. It keeps most people in ketosis and barely raises insulin, which is why some call it a fat fast.

Calories	~200-250 kcal per cup (1 tbsp each)
Breaks a weight-loss fast?	Partial
Breaks ketosis?	No
Breaks autophagy?	Yes
Insulin impact	Minimal

Why it counts as breakfast

Butter has about 100 calories per tablespoon and MCT oil about 115 to 130, so the classic recipe adds a small meal to your coffee. Pure fat triggers little insulin, but the body runs on the energy you just drank instead of on stored fat, and a clean fast for autophagy is over.

Where it can still fit

On a keto diet, a fatty coffee can help some people stretch the morning without hunger, and it will not knock them out of ketosis. If your goal is weight loss, those 200 or more calories count like any others. Some recipes use two tablespoons of each, which pushes a single cup past 400 calories.

How much is safe

There is no amount that keeps a clean fast. If you like it, drink it as your first meal and start the fasting clock after it.

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Frequently asked questions

Does butter in coffee break a fast?: Yes. A tablespoon of butter has about 100 calories of fat, enough to end a clean fast even though it raises insulin very little.
Does bulletproof coffee break ketosis?: No for most people. It is almost pure fat, and MCT oil is turned into ketones quickly.
Is bulletproof coffee good for weight loss?: Only if it replaces a meal you would otherwise eat. Added on top of your usual food, its 200 or more calories work against a deficit.
What can I add to coffee without breaking my fast?: Cinnamon, a pinch of salt, or a zero-calorie sweetener keep black coffee fast-friendly.