Does Bubbly or LaCroix Count as Breaking a Fast?

Fourteen hours into a fast, hunger is manageable, and energy feels steady. Then comes the instinct to crack open a cold can of LaCroix or Bubbly. One second later, the doubt kicks in: did that just wreck everything?

It’s a common intermittent fasting question: Sparkling water has zero calories, but its bubbles, flavors, and carbonation still prompt real questions for anyone committed to protecting their fasting window. Here’s what the science says, brand by brand.

What “Breaks” a Fast?

The core rule: a fast is broken when calories trigger an insulin response. When there are no calories, there is no insulin spike; the fasted state continues.

Johns Hopkins neuroscientist Dr. Mark Mattson explains that after several hours without caloric intake, the body burns through stored glucose and switches to burning fat for fuel, a process called metabolic switching. That’s the engine behind most of intermittent fasting’s health benefits, and it runs on calorie restriction, not on avoiding fizzy water.

The research shows that time-restricted feeding, limiting eating to fewer than 8 hours daily, improves insulin resistance and lowers cardiovascular risk. These outcomes depend on keeping calories out during fasting. Carbonation doesn’t factor in.

Medical institutions are consistent on this. Cleveland Clinic’s registered dietitian, Julia Zumpano, RD, LD, specifically lists water, carbonated water, black coffee, and unsweetened tea as acceptable during a fasting window. Mayo Clinic dietitian Mikel Bryant defines intermittent fasting as voluntary abstinence from food and caloric beverages; plain sparkling water doesn’t qualify as either.

One important distinction: the type of fast matters. Religious fasts prohibit all intake, including water. Therapeutic dry fasts follow similar rules. But for standard 16:8 or 18:6 protocols focused on weight management and metabolic health, the rule is simply no calories. Plain carbonated water easily clears that bar.

Verdict: CO₂ gas contains no calories. Plain sparkling water does not break a fast.

Keep your fasting window on track. Use our Fasting Tracker to log every hour and stay consistent.

What’s Inside LaCroix and Bubbly?

Before overthinking the bubbles, look at the actual ingredient list.

LaCroix Sparkling Water contains only carbonated water and natural flavor extracts. Its nutrition panel lists 0 calories, 0 sugar, 0 artificial sweeteners, and 0 sodium. The natural flavors, derived from fruit essences such as citrus oils and berry compounds, have no caloric value or insulin response. LaCroix also contains no carbohydrates, fats, or proteins, making it nutritionally inert for fasting.

Bubbly, PepsiCo’s sparkling water line, follows the same formula in its core lineup: carbonated water plus natural flavor, with nothing added that shifts the body out of a fasted state.

One nuance that surfaces in fasting communities: certain LaCroix flavors contain trace citric acid, and an ingredient called limonene, a citrus-derived aromatic compound, has been classified as synthetic by the FDA despite LaCroix’s “all natural” labeling. That distinction matters for marketing lawsuits, not for fasting. Limonene and trace amounts of citric acid have no caloric value and do not elicit a measurable metabolic response.

LaCroix is also confirmed keto-compatible: no carbohydrates, no glucose spike, no disruption to ketosis. The conditions for ketosis and intermittent fasting are essentially the same: no caloric intake, no insulin trigger. Quick label check: If the ingredients are carbonated water and natural flavor, and the nutrition panel says 0 calories and 0g sugar, the water is fasting-safe.

Read Does Bone Broth Break a Fast? A Comprehensive Guide

Does Carbonation Have Any Effect on Your Fast? 

CO₂ itself has no caloric value. The Amos Institute’s breakdown of fasting-safe beverages confirms that carbon dioxide dissolved in water produces no metabolic response; the fast stays biochemically intact. 

Carbonation interacts with the body in two ways worth understanding. 

The hunger hormone effect: Carbonation can stimulate ghrelin, the hunger hormone, in some people, making hunger more acute. This isn’t universal, but it’s documented. If LaCroix consistently makes a fast harder, still water is the fix. 

The satiety effect: For many, the opposite is true: carbonation physically distends the stomach, triggering short-term satiety signals to the brain. Many experienced fasters use a can of sparkling water during hours 12 to 15 of a 16:8 window, when hunger peaks, to push through without breaking early.

GI sensitivity: Carbonation warrants extra caution for people with GERD or IBS. Research cited by PrimeHealth notes carbonation can raise gastric pressure, worsening symptoms in sensitive individuals. About 1 in 7 Americans reports bloating or gas from carbonated drinks. Fasting already stresses the digestive system, and added carbonation-induced bloating isn’t helpful for everyone.

If you are unsure whether your current drink choices are keeping the fast intact, ask our AI Assistant for a clear answer based on your specific protocol.

Flavored Sparkling Waters: Where It Gets Tricky

LaCroix and standard Bubbly are clean. The risk shows up when stepping outside those two core lines into the larger sparkling water market.

Research reviewed by PrimeHealth found that up to 15% of sparkling water brands contain added sugars or artificial sweeteners that could break a fast. Brand familiarity is not a substitute for reading the label. Artificial sweeteners are a major concern: sucralose, aspartame, and acesulfame potassium are found in many flavored sparkling waters. Cleveland Clinic warns these can end a fast. 

The possible reason: the body detects sweetness, expects glucose, and releases a bit of insulin even with zero calories. Disruption depends on the sweetener and the person, but the safest option is to avoid them when fasting.

Healthline’s medically reviewed guide on what breaks a fast, updated in April 2025, clearly states that zero-calorie beverages without sweeteners are generally safe, while anything with artificial sweeteners warrants caution.

Products to watch: Sparkling Ice (contains sucralose), vitamin-infused sparkling waters, energy seltzers, and anything labeled “lightly sweetened.” These are not the same product as plain LaCroix or Bubbly, even when the packaging looks similar.

Label the checklist before drinking during a fast:

• Calories: 0
• Total sugars: 0g
• Ingredients: carbonated water and natural flavor only
• No sucralose, aspartame, stevia, or acesulfame potassium listed

Run through those four points, and the decision is made in under ten seconds.

How to Use Sparkling Water to Fast More Effectively

The better question isn’t just whether LaCroix breaks a fast; it’s whether it makes fasting better sustainable over time.

Keeping hydrated during the fasting window directly reduces false hunger signals. Dehydration mimics hunger, and many people break their fast early, not because they’re genuinely hungry but because hydration has slipped. A sparkling water at the right moment can extend a fast by an hour or more without discomfort.

Research confirms that calorie-free carbonated water produces no metabolic response and can function as an appetite suppressant during fasting. For many people on a 16:8 schedule, a can of LaCroix or Bubbly between hours 12 and 15 replaces what would otherwise be a premature meal.

A few practical guidelines for using it well:

• Limit to two or three cans per day. Excessive intake introduces carbonic acid at levels that can erode dental enamel over time. Sip rather than gulp, and don’t substitute sparkling water for the bulk of daily hydration.
• Alternate with still water. Still water moves through the system more efficiently and avoids the GI side effects that carbonation can occasionally cause on an empty stomach.
• Time to hunger peaks. On a 16:8 protocol, most people hit peak hunger between hours 12 and 15. That’s the window for sparkling water, not the first thing in the morning when hydration requirements are more straightforward.
• Test ghrelin sensitivity. Spend three to five days fasting with sparkling water, then three to five without. Track whether hunger levels differ. The answer becomes clear quickly, and it varies enough between individuals that personal testing beats any general recommendation.

The Bottom Line

Plain LaCroix and Bubbly do not break an intermittent fast. They contain zero calories, zero sugar, and no artificial sweeteners; the three factors that actually disrupt a fasted state. Johns Hopkins, the Cleveland Clinic, and Mayo Clinic all confirm that calorie-free fluids preserve the fasted state.

The real watchpoints are narrow. Carbonation may increase hunger via ghrelin in some people, so test it for yourself. Those with GERD or IBS should limit sparkling water during fasting windows. And 15% of sparkling water brands contain sweeteners or sugars that sincerely disrupt a fast, so reading the label every time is unavoidable.

Stick to plain carbonated water with no sweeteners, and the fizz works in the fast’s favor, not against it.

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