Does sparkling water break a fast? Plain sparkling water does not break a calorie-based fast such as 16:8 intermittent fasting, because it is just water and carbon dioxide with zero calories and zero sugar. Two cases change the answer. Flavored sparkling waters made with juice or sweeteners can add calories or sweeteners you may want to avoid, and before a fasting blood test the National Library of Medicine says to drink plain water only, not flavored carbonated water.
Below we sort common sparkling drinks into fine and not fine for fasting, using label figures, and look at the two questions people ask most: sweeteners and hunger.
Does sparkling water break a fast if it is plain?
No, in our view, for any fast that is defined by calories. Time-restricted eating plans such as 16:8 define the fasting window as no calories. In the TREAT trial published in JAMA Internal Medicine, for example, the 16:8 group was told to eat from noon to 8 p.m. and to “completely abstain from caloric intake” from 8 p.m. until noon the next day.
Plain sparkling water, seltzer and unflavored mineral water have no calories to abstain from. Carbonation is carbon dioxide dissolved in water; it adds fizz and a little acidity, not energy. Plain sparkling water also hydrates you like still water, which our guide to whether sparkling water hydrates you covers.
The exception is a fast that rules out all drinks, such as a dry fast. Then sparkling water breaks it like any other drink.
Which sparkling waters are fine while fasting?
Read the nutrition panel. Anything with calories or sugar is outside a strict fasting window. Here is how common types compare:
| Drink | Calories | Sugar or sweetener | Fine for a calorie fast? |
|---|---|---|---|
| Plain seltzer or sparkling water | 0 | None | Yes |
| LaCroix (natural essence flavors) | 0 | None | Yes |
| Spindrift Grapefruit, 12 oz can | 17 | 3 g sugar from real juice | No, strictly |
| Sparkling Ice, 17 oz bottle | 5 | Sucralose | Gray area |
| Tonic water, 12 oz can | About 120 | About 31 g sugar | No |
Spindrift figures are from the can’s nutrition panel as listed by retailers; Sparkling Ice is from our Sparkling Ice review; tonic water is from USDA data in our guide to sparkling water vs tonic water. Tonic surprises people: it is a soft drink, not a water.
Spindrift is a good drink, as our Spindrift review explains, but its flavor comes from real juice, so it belongs in your eating window.
Can I drink La Croix while fasting?
Yes. National Beverage, the company that makes LaCroix, describes it as having “zero calories, zero sweeteners and zero sodium,” with flavor from natural essence rather than juice. That puts it in the same group as plain sparkling water. Our LaCroix review covers the ingredients in detail. Check the can if you buy a newer or limited line, since labels can change.
Do sweeteners in flavored sparkling water break a fast?
By calories, no: sucralose and similar sweeteners add almost none. The open question is whether the sweet taste triggers an insulin response. The evidence we found does not show that for sucralose on its own. In a small crossover study of 8 healthy adults who had fasted, drinking sucralose did not raise insulin, GLP-1 or appetite compared with water (Ford and colleagues, European Journal of Clinical Nutrition, 2011).
Eight people is a small study, and it tested one sweetener at one dose. Our view: if your fast is for weight control, a sucralose-sweetened sparkling water is unlikely to undo it. If you fast for a medical reason or follow a strict protocol, stick to unsweetened sparkling water so there is nothing to argue about.
What we would buy for this job
- SodaStream Terra sparkling water maker, starter kit with one 60 L CO2 cylinder: turns tap water into plain sparkling water, so there is nothing in the glass but water and carbon dioxide. Skip the flavor drop during your fasting window.
As an Amazon Associate, Complete Water Guide earns from qualifying purchases. Prices change, so check the listing.
Can sparkling water make you hungrier while fasting?
Possibly, though the evidence is thin. A 2017 study in Obesity Research & Clinical Practice found that carbon dioxide in drinks raised the hunger hormone ghrelin in male rats, and that ghrelin also rose in 20 healthy young men after carbonated drinks compared with controls. The rat part ran for about a year; the human part was a single small test.
We would not avoid sparkling water because of one study. Many people find the fizz fills them up and makes a fasting window easier. Watch how you feel: if bubbles leave you hungrier by mid-morning, switch to still water until you eat.
Can you drink sparkling water before a fasting blood test?
Ask your doctor or lab, but the default answer is no. MedlinePlus, from the National Library of Medicine, says fasting for a blood test means you “should not eat or drink anything, except plain water” for several hours, and specifically says to “avoid lemon-flavored or flavored carbonated water, which may contain sugars or artificial sweeteners.”
Plain unflavored seltzer has no sugar, but lab instructions say plain water, so we would drink still water before the draw and save the bubbles for after. Our guide to drinking water before a fasting blood test covers how much to drink and why it helps.
What drinks will not break a fast?
For a calorie-based intermittent fast, these have zero or almost zero calories when you drink them plain:
- Still water
- Plain sparkling water, seltzer and unflavored mineral water
- Unsweetened essence-flavored sparkling water, such as LaCroix
- Black coffee and plain tea, with no milk, cream or sugar
Anything with juice, milk, sugar or alcohol has calories and belongs in your eating window. Sweetened zero-calorie drinks fall in the gray area above. For a broader look at fizzy drinks and health, see our guide on whether sparkling water is good for you.
Frequently asked questions
Does sparkling water break a fast?
Plain sparkling water does not break a calorie-based fast such as 16:8 intermittent fasting, because it has zero calories and zero sugar. Flavored versions with juice or sugar do add calories, and fasting blood tests call for plain water only.
Can I drink sparkling water when fasting?
Yes, if it is plain or flavored only with natural essence and has zero calories on the label. If the fizz makes you hungrier, switch to still water during the fasting window.
Can I drink La Croix while fasting?
Yes. Its maker describes LaCroix as having zero calories, zero sweeteners and zero sodium, so it fits a calorie-based fast. Check the label on any new or limited flavor.
Does Sparkling Ice break a fast?
It is a gray area. A 17 ounce bottle has 5 calories and is sweetened with sucralose. One small study found sucralose did not raise insulin in fasted adults, but strict fasters should choose unsweetened sparkling water.
Can I drink sparkling water before a fasting blood test?
Not unless your doctor says so. MedlinePlus says to drink nothing except plain water and to avoid flavored carbonated water before a fasting blood test.
What drinks will not break a fast?
Still water, plain sparkling water and unsweetened essence-flavored sparkling water have zero calories, and black coffee and plain tea have almost none. Juice, milk, sugar and alcohol all break a calorie-based fast.
Sources
- Lowe DA and colleagues, Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters, JAMA Internal Medicine, 2020 (TREAT trial): fasting window defined as no caloric intake.
- Ford HE and colleagues, Effects of oral ingestion of sucralose on gut hormone response and appetite in healthy normal-weight subjects, European Journal of Clinical Nutrition, 2011.
- Eweis DS, Abed F, Stiban J, Carbon dioxide in carbonated beverages induces ghrelin release and increased food consumption in male rats, Obesity Research & Clinical Practice, 2017.
- MedlinePlus, National Library of Medicine: Fasting for a Blood Test.
- National Beverage Corp. statement on LaCroix (zero calories, zero sweeteners, zero sodium); Spindrift Grapefruit nutrition panel as listed by retailers (17 calories, 3 g sugar per 12 oz can).
