Does Sparkling Water Break a Fast?
Quick Answer: No — plain sparkling water does not break a fast. It's water and carbon dioxide. Zero calories, zero insulin response, zero impact on autophagy. Drink it freely during your fasting window.
Why Sparkling Water Doesn't Break a Fast
Sparkling water — whether it's plain seltzer, club soda, or a naturally carbonated mineral water — contains nothing but water and dissolved CO2 gas. The carbonation is produced by dissolving carbon dioxide under pressure. When you drink it, the CO2 is released as bubbles and you burp it out.
A standard 12 oz can or bottle of plain sparkling water contains:
- 0 calories
- 0g carbohydrates
- 0g protein
- 0g fat
- 0 insulin response
This makes it one of the easiest fasting questions to answer. Sparkling water is as fasting-safe as still water.
The CO2 Question
Some people wonder whether the carbonic acid formed when CO2 dissolves in water (H2O + CO2 = H2CO3) has any metabolic effect. It doesn't. Carbonic acid is extremely weak and is fully processed by your lungs and kidneys as part of normal acid-base regulation. It has no caloric value and no insulin-signaling properties.
What About Flavored Sparkling Waters?
This is where you need to pay attention:
Plain carbonated mineral water (Perrier, S.Pellegrino, etc.): Zero calories, fasting-safe. The minerals (calcium, magnesium, bicarbonate) are present in trace amounts and have no caloric or insulin impact.
Naturally flavored sparkling water (LaCroix, Bubly, Waterloo): These use "natural flavors" — typically fruit-derived aromatic compounds with no sugar or calories. They are fasting-safe. A 2020 analysis confirmed LaCroix and similar products contain no fermentable sugars.
Sparkling water with added fruit juice: Some products (certain Spindrift varieties, sparkling lemonades) contain actual fruit juice and list calories. These break your fast. Check the nutrition label.
Tonic water: Not fasting-safe. Standard tonic water contains ~32 calories and 8g of sugar per 8 oz. It's a sweetened mixer, not a water.
Club soda: Just carbonated water with trace sodium bicarbonate and potassium — zero calories and fasting-safe.
Does Carbonation Affect Hunger or Digestion?
There's mild evidence that carbonated water can increase feelings of fullness by stretching the stomach. For fasting, this is a feature, not a bug — sparkling water can be a useful tool for managing hunger during a fasting window without breaking the fast.
One small concern: high carbonation intake can cause gas, bloating, or acid reflux in sensitive individuals, especially on an empty stomach. This is a comfort issue, not a fasting issue.
Sparkling Water vs. Diet Soda
Both are zero-calorie, but they're not equivalent for fasting purposes. Diet soda contains artificial sweeteners that may trigger a cephalic phase insulin response in some people. Sparkling water has no sweeteners at all.
If you're choosing between the two, plain sparkling water is the cleaner choice. See does diet soda break a fast for the full comparison.
Bottom Line
Plain sparkling water is completely fasting-safe. So is club soda. So is naturally flavored sparkling water (LaCroix, Bubly, etc.). The only sparkling waters to avoid are those with added juice, sugar, or calories — and tonic water.
For the full guide on what drinks are and aren't safe during a fast, see what drinks break a fast. And for the master framework, see what breaks a fast.
FAQ
Does LaCroix break a fast? No. LaCroix contains zero calories and no sweeteners. It's fasting-safe.
Does Perrier break a fast? No. Plain carbonated mineral water has zero calories and no metabolic impact on fasting.
Does tonic water break a fast? Yes. Tonic water contains sugar and roughly 32 calories per 8 oz.
Can sparkling water help with fasting hunger? Yes — the carbonation creates a feeling of fullness that can help manage hunger during a fasting window.
Is club soda the same as sparkling water for fasting? Yes. Club soda is just carbonated water with added minerals (sodium bicarbonate, potassium sulfate). Zero calories, fasting-safe.
References: Anton SD, et al. "Flipping the Metabolic Switch." Obesity. 2018. Cuomo R, et al. "Effects of carbonated water on functional dyspepsia and constipation." Eur J Gastroenterol Hepatol. 2002.