Does MCT Oil Break a Fast?

Reviewed by the FastTrack team · Updated June 2026
Short answer: Yes

MCT oil breaks a fast. It is pure fat with around 100 calories per tablespoon, so it ends a calorie or autophagy fast, even though it does not raise insulin or break ketosis.

Calories~100-115 kcal per tbsp
Breaks a weight-loss fast?Yes
Breaks ketosis?No
Breaks autophagy?Yes
Insulin impactNone

Why MCT oil breaks a fast

MCT oil is concentrated fat, about 100 to 115 calories per tablespoon. It has no carbohydrate or protein, so it does not raise insulin or break ketosis, which is why it is popular on keto. But those are still calories, so MCT oil breaks a fast defined by calorie restriction and it shuts down autophagy.

Fat fasting is not true fasting

Adding MCT oil or butter to coffee, sometimes called a fat fast, can keep you in ketosis and curb hunger, but it is not a true fast. If your goal is appetite control while staying in ketosis, it works. If your goal is autophagy or calorie restriction, MCT oil breaks the fast.

How much is safe

There is no calorie-free amount of MCT oil; a tablespoon adds about 100 calories, which breaks a calorie or autophagy fast.

Track your fasts with confidence

FastTrack times your fasts, your eating window and your progress, with a plan built around your goals.

Get your free plan

Frequently asked questions

Does MCT oil break ketosis?
No, it is pure fat and supports ketosis.
Does MCT oil break a fast?
Yes, its calories break a calorie or autophagy fast.
Is bulletproof coffee fasting?
No, the added fat makes it a fat fast, not a true fast.
Does MCT oil raise insulin?
No, fat does not meaningfully raise insulin.

Better choices while fasting