What Breaks a Fast? Coffee, Water, Gum, Supplements & More

Last updated: July 6, 2026 · by Clustle Studio

The honest short answer: calories break a fast. Plain water, black coffee and unsweetened tea are fine. Anything with calories — milk, sugar, juice, BCAAs — breaks it. A few things are genuinely "it depends," and the reason is that what counts as breaking a fast depends on your goal: simple weight loss, ketosis, or autophagy.

Quick reference: does it break a fast?

Use this as a fast lookup. Details and the "why" are below the table.

These are general guidelines for healthy adults, not medical rules. Individual responses vary.

The one idea that clears up 90% of the confusion

Most "does X break my fast?" arguments happen because people are chasing different goals without saying so. There are three common ones:

• Weight loss / calorie control — here what matters is total calories. A few calories from a squeeze of lemon or a stick of gum won't undo anything. This is the most forgiving goal.
• Ketosis / fat adaptation — you want to keep insulin low. Anything that spikes insulin (sugar, and for some people sweeteners) matters more than raw calories.
• Autophagy / a "clean" fast — the strictest interpretation. Here people avoid anything that isn't water, sometimes even black coffee, because they want zero metabolic input. Note that autophagy timing in humans is not firmly established (see our fasting stages guide).

So before you ask "does this break my fast?", ask "break it for which goal?" For everyday weight-loss fasting, the bar is simply: keep calories near zero.

Drinks, one by one

Water — never breaks a fast

Still, sparkling and mineral water are all fine, and staying hydrated actually helps with the headaches and fatigue people sometimes feel while fasting. Just don't add anything caloric or sweetened.

Black coffee — fine for almost everyone

Plain black coffee has only a couple of calories per cup and does not meaningfully break a fast for weight-loss or ketosis goals. Some evidence suggests it may even support fat metabolism. The moment you add milk, cream, sugar, or a flavored syrup, though, you're eating — that breaks it. "Bulletproof" coffee with butter or oil definitely breaks a fast.

Tea — fine when unsweetened

Green, black, oolong and herbal teas are all fasting-friendly without sweetener. They're a good way to get variety when you're tired of water.

Diet soda & artificial sweeteners — the honest "it depends"

Zero-calorie sweeteners (sucralose, aspartame, stevia) don't add calories, so on a strict calorie basis they don't break a fast. But two real caveats: some people find sweeteners trigger hunger and cravings, and there's ongoing debate about whether certain sweeteners nudge insulin. For a relaxed weight-loss window, a diet soda is unlikely to hurt. For a strict fast, skip it.

Foods & supplements people ask about

Chewing gum

Sugar-free gum has around 1–5 calories per piece. For weight-loss fasting that's a rounding error and can curb appetite. Strict fasters avoid it on principle.

Apple cider vinegar

A teaspoon to a tablespoon in water has only a few calories and is generally fine — some people use it to blunt hunger. Sweetened "ACV drinks," or large quantities, add enough to matter.

Bone broth

Often recommended for fasting, but be clear: broth has calories and protein, so it does break a clean fast. It can be a gentle way to end a fast or to get through a very long one, but it is food.

BCAAs, protein & collagen

These contain calories and stimulate an insulin response, so they break a fast. If your goal is muscle retention around workouts you may choose to have them anyway — just know you're technically eating.

Vitamins, electrolytes & medication

Plain pills, sugar-free electrolytes and most vitamins don't break a fast. Gummy vitamins and anything with sugar or oil do. Medication is different: always take prescribed medicine exactly as your doctor instructs, including with food if directed — never skip or delay it to protect a fast.

Frequently asked questions