This has got to be one of the most frequent questions I see:
“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 for 12-24 hours places you in rarefied company. That’s 95th percentile stuff. You’re ahead of the game simply by being open to the idea of not eating every hour. Take heart in that. Some coffee with cream midway through doesn’t take away from what you’re accomplishing.
But I know you guys, and I know you love the minutiae. I know it because I love it, too. It’s fun, even if it gets us into trouble sometimes. So let’s dig right in.
First, does black coffee break a fast?
Put another way.. Does coffee interfere with the benefits we’re seeking from a fast? Depends on the benefits you’re seeking (and what you put in the coffee).
Let’s look at some of the most common benefits first and if/how coffee affects them.
Common Benefits of Fasting: Does Coffee Help/Hinder?
Fasting is a quick and easy (or simple) way to get into ketosis. You have little choice in the matter. Since you’re not eating anything, and your body requires energy, you break down body fat for energy. And because you’ve only got fat “coming in,” you’ll quickly start generating ketone bodies. If coffee stops ketosis, it’s probably breaking the fast.
A recent study  found that taking caffeine acutely upregulates ketosis in humans.
Fat-burning is another important aspect of fasting. Since we’ve already shown that coffee increases ketosis, I think it’s pretty obvious that coffee also increases fat mobilization and burning.
Over the long term, fasting is an effective way to improve insulin sensitivity and glucose tolerance. Most things that make you better at burning fat and expending, rather than storing, energy—like exercise, low-carb diets, weight loss in general—tend to improve insulin sensitivity over time. But the sometimes counterintuitive piece to all this is that in the short term, fasting can reduce insulin sensitivity. This is a physiological measure  the body takes to preserve what little glucose remains for the brain. All the other tissues become insulin resistant so that the parts of the brain that can’t run on ketones and require glucose get enough of the latter to function.
Coffee has a similar effect. Acutely, it reduces insulin sensitivity and glucose tolerance  (so don’t eat pastries with your coffee). 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 .
Cellular cleanup. Pruning. Entropy dictates that all things are constantly speeding toward disorder. Things fall apart, in other words. That applies to our cells and the tissues they comprise, too. But because we are biological beings rather than inert objects, we can respond to and resist the descent into disorder. Autophagy is one of the ways in which we keep our cells healthy and maintained, pruned, and trimmed of damaged bits. Fasting is one of the best ways to induce autophagy. It’s one of fasting’s major selling points. If coffee destroys autophagy, that’d be a big mark against coffee and a sure sign it’s breaking the fast.
Good thing coffee doesn’t appear to hamper autophagy. At least in mice, both caffeinated and decaffeinated coffee induce autophagy in the liver, muscle tissue, and heart .
Adenosine monophosphate-activated protein kinase, or AMPK, is an enzyme that inhibits fat storage and promotes fat burning. It activates antioxidant networks, triggers autophagy, and promotes mitochondrial biogenesis. A major benefit of fasting is that it causes a big uptick in AMPK activation. Other things do, too, like exercise, basic calorie restriction, and any situation where energy is being deprived or expended, but fasting is one of the more reliable paths.
Okay, so black coffee doesn’t seem to break the fast in any meaningful sense. What about all the things people like to add to coffee?
Common Additions to Coffee
Coffee With Butter/MCT Oil/Coconut Oil?
Technically, it breaks the fast. You’re ingesting calories (depending on how much fat you add, it could be a significant number of calories), and calories break the fast. But pure fat has little to no effect on insulin, blood glucose, or any of the other measurements that indicate a “broken fast.”
You won’t burn as much body fat. You’ll still burn plenty of body fat.
It will help you fast longer. Adding a little fat to your coffee can make fasting more tolerable. If you can only manage 12 hours on black coffee but a couple teaspoons of coconut oil help you go 24, the coconut oil might be a good addition.
It shouldn’t affect autophagy. Protein ingestion interrupts autophagy. Butter has a tiny amount of protein that shouldn’t interfere.
Coffee With Heavy Cream?
An ounce of cream has almost a gram each of carbohydrate (lactose) and protein. That. Some cream in your coffee won’t affect your fat burning very much, but it probably will inhibit some autophagy.
That said, remember that ketogenic diets increase autophagy too , and those definitely include food. This is all a matter of degree. It’s not a binary on-off switch. Less autophagy isn’t zero autophagy.
Coffee With Almond/Other Nut Milk?
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 Cinnamon/Cocoa/Nutmeg?
Cinnamon is fine. It tends to reduce insulin resistance , especially the kind you get after a bad night’s sleep.
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. If you add cocoa, use defatted cocoa powder. Adding too much of the cocoa powder with fat included will reduce the effects of fasting.
Nutmeg is fine, too. Just avoid psychotropic doses .
Coffee With Stevia?
When you eat it with a snack containing 290 calories, stevia lowers glucose and insulin levels . I see no mechanism by which stevia could make the situation worse without a meal.
Coffee With Monkfruit Extract?
Monkfruit extract has an effect  similar to stevia. It’s fine.
Coffee With Artificial Sweeteners?
There’s no good evidence they’ll impair the metabolic response to fasting , but there are other unwanted 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.
When You’re At a Coffee Shop
Order black coffee: drip, pour-overs, espressos, Americanos. That’s the most surefire way to maintain the fast.
Ask for heavy cream, don’t use the “cream.” The “cream” coffee shops tend to set out for customer use is actually half-and-half: half milk, half cream. That gives it a significant protein and carb load that will inhibit the effects of the fast. Instead, if you absolutely need something to add to your coffee, ask the staff for heavy cream.
Avoid nut milks. 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, far too much for your fast (even if it’s unsweetened).
That’s about it for coffee and fasting. 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!
To read more about coffee, visit:
- The Definitive Guide to Coffee 
- Do Coffee Brewing Methods Matter for Health? 
- 14 Ways to Make Coffee Healthier 
- 7 Healthy Coffee Ideas for Every Primal Taste 
- Does Coffee Decrease Insulin Sensitivity? 
To read more about fasting, check out:
- Intermittent Fasting for Women 
- More on Women and Fasting 
- Fasting Versus Carb Restriction 
- Long Fasts: Worth the Risk? 
- Does the Fasting Mimicking Diet Live up to the Hype? 
- Does Bone Broth Break a Fast?