Does Bulletproof Coffee Break a Fast? The Full Story, with Examples

Does Bulletproof Coffee Break a Fast?

Drinking black coffee while you fast is a pretty reasonable thing to do. It has no calories, and in most cases doesn’t “break” a fast.  

But what if you add a bunch of fat to your coffee, and call it “Bulletproof” Coffee…

Does Bulletproof Coffee break a fast?

Here’s the short version:  

In general, coffee with added butter, cream, or MCT oil is one of those “training wheels” that can make fasting easier for beginners. It’s fine to use it when you’re starting out, but it’s not something you need to use forever.

If you want to maximize the health benefits of fasting, you should probably wean off Bulletproof Coffee (and other high calorie drinks) eventually. 

For the whole story, read on. 

What is “Bulletproof” Coffee?

“Bulletproof Coffee” is coffee with butter and/or MCT oil mixed in.

bulletproof coffee has coffee, butter, and MCT oil

Bulletproof is a brand name, but many people make homemade versions as well. Here’s one example

Bulletproof Coffee can also be called “butter coffee”, or “keto coffee” (because it’s high fat and low carb, like a ketogenic diet).

Here’s the basic recipe:

  • One cup of coffee
  • 1-2 tbsp of butter
  • 1-2 tbsp of MCT oil

Why Do People Drink Bulletproof Coffee?

Basically, the idea is to take in energy without consuming significant amounts of protein or carbs (just fat).

That way, your body can use the fat for energy, and also turn some of it into ketones (the alternative energy source your brain uses when you fast), without significantly raising your blood sugar or insulin levels (more about insulin below).

Subjectively, some people say it makes them feel more energetic, improves mental clarity, or controls their hunger.

(Personally, I’ve never tried Bulletproof Coffee. But I’ve noticed some of those same benefits–like increased energy and focus–from consuming a little extra fat while I fast.) 

Does Bulletproof Coffee Break Your fast?

Let’s start by talking about the coffee. Then we’ll talk about the added fats. 

Note: Most of the info below applies to both daily “intermittent” fasting and multi-day “extended” fasting. The only exception would be for something like autophagy that doesn’t start until you’ve been fasting for multiple days.

Does Black Coffee Break a Fast?

Black coffee means there is no sugar or cream added, so it basically has no calories.

In most cases, drinking things that have zero calories is fine when you’re fasting.

(One notable exception would be artificial sweeteners–such as aspartame or sucralose–because even though these have zero calories, they also have several harmful effects.)

You can drink black coffee, and you’ll still get plenty of health benefits from fasting.  

For example, coffee won’t stop you from burning body fat or lowering your blood sugar.

does black coffee break a fast - summary chart

(Side Note: In people with diabetes, high caffeine intake results in higher blood sugar after a carb-rich meal. But the caffeine doesn’t appear to raise fasting blood sugar, which is what we’re talking about here.)

Bottom line?

For most people, it’s reasonable to drink black coffee while fasting. You’ll still get a lot of health benefits, and you can get your caffeine fix as well. 🙂

Does Butter Coffee Break a Fast?

We’ve established that drinking black coffee while fasting is probably okay, at least for most people.

But what if you add butter to the coffee? Does drinking melted butter break your fast?   

Consider for a moment what happens when you eat (or drink) butter.  

Butter consists almost entirely of fat. When you eat fat, it doesn’t really raise your blood sugar, but you do take in a lot of energy (aka calories).

Why does this matter?

If you eat a lot of butter, your body won’t need to tap into its own energy stores as much. That means you won’t burn as much of your own body fat.  

For example, if you put about 4 total tbsp of butter in your coffee each day, for one week, that’s about one more pound of body fat that you could have burned if you didn’t drink the butter. 

Bottom line?

If your goal is to burn body fat, try to limit how much food energy you take in while fasting, including from dietary fats (like butter).   

The more fat you consume while fasting, the less of your own body fat you’ll burn.

Does Butter Coffee Break a Fast - summary chart

Does MCT oil in your coffee break a fast?

The “MCT” in MCT oil stands for “medium chain triglyceride”.

This means it has smaller (“medium”-sized) fat particles that your body can digest more quickly, compared with most other types of fat.  

Why does this matter?

Because of their small size and quick digestion, MCT’s are turned into ketones more easily than other types of fat. This means you’ll likely have higher blood ketone levels if you consume MCT oil.

MCT oil features

Just like butter, MCT oil probably won’t raise your blood sugar while fasting. 

For example, the first time I did an extended fast, I ate a few spoonfuls of coconut oil (which contains MCT’s) each day, and my blood sugar stayed nice and low. 

Also like butter, MCT oil contains a lot of energy, which means you’ll burn less of your own body fat if you drink it when you fast.

Bottom line?

Using some MCT oil while fasting is basically fine, but the more of it you use, the less of your own body fat you’ll burn.

You’ll still get a lot of health benefits from fasting with MCT oil, so go ahead and use it if it makes things easier or more pleasant for you. 

(Note: I also wrote a more comprehensive article about whether MCT oil breaks a fast.)

Does Bulletproof Coffee Spike insulin? 

Insulin is the hormone that helps your body store energy, especially after you eat carbs.

Basically, if you eat carb-heavy food (like pasta, bread, crackers, french fries, etc), your body pumps out insulin to help push these carbs into your fat cells and muscles. 

When you fast, your insulin level goes down, because no carbs are coming in. 

graph of insulin going down while fasting

Coffee alone won’t raise insulin levels while fasting. But what about the butter or MCT oil in Bulletproof Coffee? 

Here’s what basic physiology tells us:  

Eating carbs raises insulin a lot, eating protein raises insulin a little, but eating fat doesn’t really raise insulin at all. 

So consuming butter or MCT oil with your coffee will have little, if any effect on your insulin levels.

Bottom line? 

It’s highly unlikely that Bulletproof Coffee (or any other dietary fats) will spike your insulin.

Does Bulletproof Coffee Stop Autophagy?

Autophagy is when cells inside your body start recycling old, worn out proteins.

Basically it’s like “spring cleaning” inside your cells, and fasting is one of the most potent stimulators of autophagy.

fasting autophagy timeline graph / chart

Does regular black coffee prevent autophagy while fasting?

In mice, coffee actually seems to increase the rate of autophagy, but I don’t think we have any data about this in humans. Maybe coffee increases the rate of autophagy in humans as well…maybe it doesn’t. Since we aren’t mice, we don’t really know. 🙂

Now, what if you add butter or MCT oil to your coffee, will this slow down autophagy?

As a rule of thumb, remember that low energy intake stimulates autophagy, while high energy intake prevents autophagy.

What does this actually mean?

The more food energy (i.e. calories) you consume, the less autophagy you can expect to happen.

For example, if you consume an extra thousand calories of butter and MCT oil per day while “fasting”, there’s probably not a lot of autophagy happening in your body.

Bottom line?

If your main goal is to stimulate autophagy while you fast, you should reduce your energy intake from food as much as possible. This includes reducing the amount of dietary fats like butter or MCT oil that you consume.

Does Heavy Cream in Coffee Break a Fast?

We’ve talked a lot about drinking coffee with butter or MCT oil, but what about the more traditional coffee with cream? Will drinking coffee with cream break your fast? 

Cream is a slightly different animal compared with butter or MCT oil, because it’s not quite as “pure” of a fat – it contains a little bit more protein and carbohydrate (about 0.8 grams of each, per serving). 

Cream is still mostly fat, so just like butter and MCT oil it won’t significantly raise your blood sugar or insulin levels. But it may have a small effect.

And don’t forget, the more fat you consume while fasting, the less of your own body fat you will burn.

It also makes you less likely to rev up autophagy, as described above.

does heavy cream in coffee break a fast - summary chart

Bottom line?

If you find it helpful, go ahead and use a small amount of cream in your coffee while you fast.  

Over time, try to reduce the amount of cream you’re using, as it may slow down your progress towards some fasting goals (like losing body fat or stimulating autophagy).

What About Coffee and Sleep?

Some people find it harder to sleep when fasting for multiple days. If this is the case for you, then definitely don’t drink any coffee late in the day!  

After you drink a cup of coffee, it takes about 12 hours for your body to remove 75% of the caffeine that you consumed.

For example, if you get 100 mg of caffeine from a cup of coffee at noon, about 25 mg of caffeine are still floating around in your bloodstream at midnight. That’s not a recipe for great sleep.

Ideally, try to avoid any caffeine after noon, whether you’re fasting or not.

(Similarly, I mentioned a couple affects that alcohol has on sleep in my post about whether alcohol breaks a fast.)

Conclusion – Does “Bulletproof Coffee” break a fast?

For most people in most situations, drinking plain black coffee does not “break” a fast.

You’ll still get most of the health benefits of fasting, so it’s probably worth drinking coffee if it makes it easier or more pleasant for you to fast.

The same thing is kind of true about “Bulletproof” Coffee…but the situation changes a little.

If you add butter or MCT oil to your coffee, it probably won’t raise your blood sugar or insulin levels, but it will decrease the amount of your own body fat that you burn.

Adding cream to your coffee is very similar to adding butter or MCT oil, with the exception that cream has slightly more protein and carb content. That means it may raise your blood sugar or insulin levels a tiny bit (probably not enough to matter for most people). 

How can you actually use this?  

Here’s what I’d recommend: 

If you like drinking black coffee while you fast, go ahead.

If you find it helpful to add butter, MCT oil, or cream to your coffee, go ahead and do that as well. But try not to overdo it.

Think of these added fats like “training wheels”: They can make it easier for you to fast, but they’re not something you need to use forever. 

As time goes on, try to use less and less butter, cream, or oil while you fast.

By weaning off of these fats, you’ll probably get even more health benefits from fasting.

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Ben Tanner, PA-C

Ben Tanner, PA-C

Ben has been practicing as a physician assistant (PA, or PA-C, similar to a doctor) in emergency medicine, urgent care, and family practice since 2014. Since 2016, he has developed an avid interest in various forms of fasting, using it to improve his own health while helping friends, family, and patients do the same.

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