I talk about intermittent fasting a lot, so I get a lot of questions about how to do it “right” to net the most benefits. By far, the most common question I receive is, “Can you drink coffee while fasting?” This is usually followed by some explanation about how the asker is happy to go for 16, 18, even 20 hours without food, but there is no way they can give up their morning cup of joe.  

So let’s talk about it. DOES coffee break a fast? 

To begin with, I’ll make the case that you shouldn’t worry too much about this stuff. That you’re even willing and able to go without a meal or snack every couple of hours places you in rarefied company. That’s 95th-percentile stuff. I wouldn’t want you stressing about the minutiae. Stress will undermine some of what you’re hoping to accomplish with fasting—less inflammation, better health, longer life. 

But I know my readers, and I know you love digging into the specifics and asking the tough questions. In this case, rather than asking whether coffee breaks a fast, I think it makes more sense to ask: Does coffee interfere with the benefits we’re seeking from a fast?

Off the top of my head, I can think of five prominent reasons why someone might practice intermittent fasting:

• To promote autophagy
• To make it easier to maintain a caloric deficit
• To improve glycemic control and insulin sensitivity 
• To “rest” the gut—that is, to give your GI tract breaks from having to digest food, usually with the goal of healing an inflamed or leaky gut
• To achieve, maintain, or get into a deeper state of ketosis

These aren’t the only reasons, and they aren’t mutually exclusive, but I’d say they cover the main ones. We want to know whether coffee affects them. 

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Does Black Coffee Break a Fast?

Let’s start with the easy question first. A large cup of black coffee contains around five calories. I know fasting purists will say that any calories break a fast. Others will tell you that you’re still fasting as long as you don’t consume more than 50 calories. However, that seems to be one of those “truisms” has become widely accepted simply because it is repeated so often, even though there’s no apparent source of validity. 

I can’t get too worked up about five calories. That’s not nearly enough to meaningfully affect insulin, blood sugar, or ketone levels. By that standard, black coffee doesn’t break your fast. Likewise, your gut won’t have to work hard to digest a cup of coffee. (The caffeine can trigger IBS symptoms, though.)

Now the autophagy question is interesting. I did my best to figure out how many calories you have to ingest to disrupt autophagy, but there doesn’t appear to be one. We simply don’t know enough about autophagy in humans, and experts disagree about where the threshold is for turning off, or at least significantly reducing, autophagy. I wouldn’t personally worry about a cup or two of black coffee since we know that factors other than fasting—caloric restriction¹ and exercise,² to name two—also promote autophagy. 

Bottom line: Black coffee doesn’t break a fast.

But most people don’t break their coffee black, so…

Can You Drink Coffee with Creamer or Other Additives While Fasting?

The answer to this one isn’t straightforward. Again, purists will say the answer is obviously no since anything you add will have calories. But you’re asking me, and I’m going to say it depends on what you’re adding to your coffee, how much, and why you’re fasting in the first place. 

If you’re trying to maintain a caloric deficit, adding several hundred extra calories to your coffee is a bad idea, but you might not mind the 50 calories in a tablespoon of heavy cream if it significantly elevates your coffee enjoyment factor. 

If ketosis is your primary objective, and you don’t care about calories, then additives are okay as long as you avoid too many carbs. The same is probably true for glucose tolerance or insulin sensitivity.

If autophagy is very important to you, stick to black coffee. I know I just said that we don’t know exactly what it takes to interfere with autophagy in humans, but we do know that protein will shut it off, so definitely don’t add protein to your coffee. Likewise, if total gut rest is your goal, go for black. 

This is all a little abstract. To put it in more concrete terms, here’s how some popular coffee additives affect fat burning (ketosis, glucose, insulin) or autophagy. 

• Coffee with heavy cream: An ounce of cream has almost a gram each of carbohydrate (lactose) and protein. Some cream in your coffee won’t affect your fat burning very much, but it probably will inhibit some autophagy.
• Coffee with butter, MCT oil, or coconut oil: Pure fat has little to no effect on insulin, blood glucose, or any of the other measurements that indicate a “broken fast.” It also shouldn’t affect autophagy. However, fatty coffees can pack several hundred calories, so it’s hard to call that “fasting.”
• Coffee with almond milk or other nut milks: As long as you’re avoiding the sweetened versions, or the ones that come fortified with extra protein, and you’re not adding a half cup at a time, a little nut milk won’t make a big difference. There is very little of anything in most nut milks.
• Coffee with stevia or monk fruit: When eaten with food, stevia seems to lower glucose and insulin levels.³ Monk fruit extract has a similar effect.⁴ I’m not worried about these zero-calorie sweeteners breaking a fast.
• Coffee with other artificial sweeteners: There’s no good evidence they’ll impair the metabolic response to fasting, but there are other effects you should want to avoid.
  
• Coffee with collagen: As much as I love (and sell) collagen, it is pure protein, and protein tends to activate mTOR and inhibit autophagy. This means that collagen in your coffee during a fast is probably fine for fat burning (and may suppress appetite, helping you fast for longer) but will reduce the benefits of autophagy.
• Coffee with cinnamon: Cinnamon is fine. It tends to reduce insulin resistance, especially the kind you get after a bad night’s sleep.
•  Coffee with cocoa powder: Cocoa powder is okay, but watch the amount. It’s a “whole legume” powder, so it has carbs, protein, and fat. Anything more than a teaspoon will overdo it.

Actually, Coffee Can Enhance the Benefits of Fasting

Rather than worrying about whether coffee breaks a fast, we should really be asking whether coffee helps a fast. Signs point to yes: 

• A recent study found that taking caffeine acutely upregulates ketosis in humans.⁵
• Acutely, coffee reduces insulin sensitivity and glucose tolerance (so don’t eat pastries with your coffee).⁶ But over the long term, it improves insulin sensitivity and glucose tolerance. Many studies find that the more coffee you drink, the lower your risk of type 2 diabetes.⁷
• At least in mice, both caffeinated and decaffeinated coffee induce autophagy in the liver, muscle tissue, and heart.⁸

How to Order Coffee At a Coffee Shop While Fasting

Order black coffee: Drip, pour-overs, espressos, Americanos. That’s the most surefire way to maintain the fast.

Add the cream yourself: That way you can add just a splash. I opt for heavy cream.

Avoid nut milks and oat milk. Coffee places often use sweetened nut milks, and they use entirely too much of it. An almond milk latte will have around 8 ounces of almond milk, more than you want if you’re fasting (even if it’s unsweetened). A cup of oat milk contains around 16 grams of carbs, so it’s a definite no-go. 

That’s about it for coffee and fasting. If you have more questions about what does or does not break a fast, chances are I covered them in my Definitive Guide to What Breaks a Fast or the Supplement Edition. If you have any further questions, don’t hesitate to ask down below. I’ll get to as many as I can in a future post.

Thanks for reading, take care, and enjoy your coffee!

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