Does flavored sparkling water break a fast?

Zero-calorie naturally flavored brands are fast-safe. Anything with sugar or juice breaks a fast.

Does tonic water break a fast?

Yes. Tonic water contains added sugar and calories.

Does carbonation affect ketosis?

No, plain carbonated water does not affect ketosis.

Can sparkling water cause bloating while fasting?

It can cause mild gas or bloating in some people, but it does not break the fast.

Does Sparkling Water Break a Fast?

Reviewed by the FastTrack team · Updated June 2026

Short answer: No

Plain sparkling water does not break a fast. With zero calories and no sugar, carbonated water has no effect on insulin and can help curb hunger during a fast.

Calories	0 kcal
Breaks a weight-loss fast?	No
Breaks ketosis?	No
Breaks autophagy?	No
Insulin impact	None

Why sparkling water is fast-safe

Unflavored carbonated water is just water and carbon dioxide. It contains no calories, sugar, or sweeteners, so it cannot raise insulin or end a fast. The carbonation can even take the edge off hunger, which helps during longer windows.

Watch flavored and tonic versions

Plain and naturally flavored zero-calorie sparkling waters are fine. Tonic water, by contrast, contains sugar and breaks a fast, and some flavored brands add sweeteners or juice. Check the label for any calories or sugar.

How much is safe

There is no real limit on plain sparkling water during a fast. If carbonation gives you gas or bloating, simply switch to still water.

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Frequently asked questions

Does flavored sparkling water break a fast?: Zero-calorie naturally flavored brands are fast-safe. Anything with sugar or juice breaks a fast.
Does tonic water break a fast?: Yes. Tonic water contains added sugar and calories.
Does carbonation affect ketosis?: No, plain carbonated water does not affect ketosis.
Can sparkling water cause bloating while fasting?: It can cause mild gas or bloating in some people, but it does not break the fast.