Steady
What breaks a fast
Does coffee break a fast? And the rest of the list.
Black coffee does not. The reason the internet cannot agree about anything else is that "breaks a fast" means three different things, and most fasting apps would rather you kept asking.
Why nobody agrees
Ask "does this break my fast" and the answer depends entirely on a question nobody asks back: what are you fasting for? There are three common reasons, they have different thresholds, and arguments online are almost always two people answering different questions at full volume.
| Your actual reason | What breaks it | Working rule |
|---|---|---|
| Eating less across the week, which is most people | Real calories. Nothing else. | Under about 25 calories, ignore it. A latte is a meal. |
| Steadier blood sugar and insulin | Carbohydrate first, protein second, fat least. | Skip sugar and anything with protein in it. Cream is the least disruptive of the add-ins. |
| Autophagy, as seen on the internet | Genuinely nobody can tell you. | It is not measurable at home and the human evidence is thin. Do not build daily rules on it. |
If you are fasting for the first reason — and you almost certainly are — then the whole question collapses into arithmetic, and the arithmetic is not close.
The list, in calories
Roughly what each one costs you
Calories per ordinary serving. The shaded band is the range below which nothing measurable happens.
The ones people argue about
A splash of milk. Nine calories. If nine calories decides whether your fast worked, the fast was not the thing that was going to work. Pour it.
Sweeteners and diet soda. No calories, so no effect on the reason most people fast. The evidence on sweeteners and appetite is genuinely mixed and keeps moving, so here is a better test than any study: drink it for a week and see whether your hard hour gets worse. If it does, skip it. That is your own data, and it beats a headline.
BCAAs and "fasting-friendly" supplements. This one is worth being blunt about. BCAA powder is protein with a marketing budget. It has calories, it is the macronutrient most likely to interrupt whatever metabolic story you were told, and it is sold specifically to people fasting. If you want it during training, fine, but do not pretend it is water.
Bone broth. Around 40 calories and genuinely satisfying, which is why people use it. It is a small snack. If it gets you from hour 13 to hour 16 and you would otherwise have eaten a meal, it is an excellent trade. Just call it what it is.
Gum, lemon, apple cider vinegar. Five calories, one calorie and three calories. None of them matter. Some people find gum makes them hungrier; some find it saves them. You will know within two days.
Electrolytes. Unsweetened ones are near zero calories and are often the actual fix for a first-week headache. Worth trying before you decide fasting does not suit you.
The rule that replaces the list
If it has fewer calories than a stick of gum and no sugar in it, drink it and stop thinking about it.
That rule covers water, coffee, tea, sparkling water, a splash of milk, most sweeteners and unsweetened electrolytes, which is everything you were actually going to drink. It takes ten seconds to learn and it is right nearly every time, which is more than can be said for a forty-item lookup table.
The reason the forty-item table exists anyway is that a question you keep asking is a reason to keep opening an app. Somewhere in this hour, a fasting app is asking someone to log a cup of coffee.
The one that actually matters
None of this is the reason fasts fail. People do not quit because of a tablespoon of milk. They quit at one particular hour, when tired, hungry and low turn up together, and no amount of correctness about coffee helps at that moment. If you have been researching drinks for a week and fasting for two days, the drinks were never the problem.
Questions people ask
Does black coffee break a fast?
No. A cup of black coffee is about two calories, which is less than the rounding error on anything you ate yesterday. It does not meaningfully affect weight loss, blood sugar or anything else you are fasting for. Drink it.
Does milk in coffee break a fast?
A tablespoon of milk is around nine calories and will not change your results. A latte is a different thing: a small oat milk latte is well over a hundred calories, which is a light meal in a cup. The line is not milk versus no milk, it is a splash versus a drink made of milk.
Do artificial sweeteners break a fast?
They carry no calories, so for the purpose most people fast for, no. The honest caveat is that evidence on sweeteners, insulin and appetite is mixed and still moving. If a sweetened drink leaves you hungrier for the next hour, that is a practical reason to skip it, and a better reason than any theory.
Does diet soda break a fast?
Not on calories, since it has none. Some people find it makes them want food, which matters more than the label does. Try it for a week; if your hard hour gets worse, that answers it for you.
What can I drink while fasting?
Water, black coffee, plain tea and sparkling water, freely. A splash of milk if you want it. Unsweetened electrolytes if you get headaches. Skip juice, sugary drinks, anything with protein powder, and anything you would describe as a treat, because those are food.
Less app. Better fasts.
Steady is a simple fasting app for iPhone: a timer for 12 to 20 hour windows, one check-in at the hour that matters, and a record that tells the truth. No account, no streak to lose, nothing leaves your phone.
Free while it is in beta. Tell us what breaks, and we will let you know when Steady reaches the App Store.