Carbonated water has a mixed effect on digestion. It can help with constipation and swallowing difficulties, but it also relaxes the valve that keeps stomach acid in place, increases belching and fullness, and may boost your hunger hormone levels. Whether it helps or hurts depends on the specific digestive issue you’re dealing with.
How Carbonation Affects Your Stomach
When you drink sparkling water, the dissolved carbon dioxide creates gas in your stomach. That gas has to go somewhere. Most of it leaves through belching, while a smaller portion gets absorbed in the small intestine or passes through the large intestine. This is why the most immediate effect of carbonated water is a feeling of fullness and an urge to burp.
Studies comparing carbonated beverages to still water show significantly higher scores for fullness, heartburn, urge to belch, and actual belch frequency after drinking carbonated drinks. The feeling of fullness peaks right after drinking and persists for several minutes. For people who already struggle with bloating or excess gas, carbonated water can make those symptoms worse. People with irritable bowel syndrome are especially prone to this, since their intestinal muscles may respond abnormally to gas and create a heightened sensation of bloating even from modest amounts of CO2.
One thing carbonation does not appear to do is change how quickly food leaves your stomach. Research measuring stomach emptying rates found that higher carbonation levels temporarily increased the size of the stomach’s lower chamber during the first 20 minutes after drinking, but this didn’t translate into any meaningful change in how fast the stomach emptied or how full people felt over time. So sparkling water won’t speed up or slow down your digestion in any significant way.
Constipation: Where the Evidence Is Strongest
The clearest digestive benefit of carbonated water comes from constipation research. In a double-blind, randomized trial, people with functional constipation drank either mineral water with added carbonation or carbonated tap water daily for six weeks. By the three-week mark, those drinking the mineral water had a statistically significant increase in bowel movements per week (an increase of about 2 extra movements) compared to the tap water group (less than 1 extra movement). Stool consistency also improved, shifting toward a softer, healthier range.
There’s a caveat worth noting. The mineral water in that study contained high levels of sulfate, calcium, and magnesium, all of which have their own effects on bowel function. Sulfate in particular has a mild laxative effect. So it’s difficult to separate how much of the benefit came from the carbonation itself versus the mineral content. Still, the carbonated tap water group also saw some improvement, just less of it. If you’re dealing with occasional constipation, carbonated mineral water is a reasonable thing to try.
Acid Reflux and the Esophageal Valve
If you have acid reflux or GERD, carbonated water is more likely to be a problem than a solution. The lower esophageal sphincter is the ring of muscle between your esophagus and stomach that keeps acid from traveling upward. In a study of healthy volunteers, all carbonated beverages reduced the resting pressure of this sphincter by 20 to 50 percent, and that reduction lasted at least 20 minutes. In 62 percent of cases, the pressure dropped low enough to reach a level that would normally be classified as sphincter incompetence, the condition that allows acid to splash back into the esophagus. Plain tap water caused no reduction at all.
This doesn’t mean a single glass of sparkling water will give you heartburn if you don’t already have reflux issues. But if you’re someone who regularly experiences acid reflux, carbonated water is working against the very mechanism your body uses to keep acid where it belongs.
Swallowing Difficulties
One lesser-known benefit of carbonated water is its effect on swallowing. The fizz in sparkling water activates sensory nerves in the mouth and throat through two different pathways: the bursting bubbles stimulate touch receptors, and the acidity from dissolved CO2 activates pain-sensing nerves that signal to brain regions involved in swallowing. This dual stimulation increases sensory input to the brain’s swallowing centers, which can help trigger and strengthen the swallowing reflex.
For people who have difficulty swallowing (a condition called dysphagia, common after stroke or in older adults), carbonated liquids can be easier to swallow than still water because they give the brain a stronger signal about where the liquid is and when to initiate the swallow.
Carbonation and Appetite
If you’ve heard that sparkling water helps with weight loss by making you feel full, the research tells a more complicated story. A study at Birzeit University found that both rats and humans who drank carbonated water had significantly elevated levels of ghrelin, the hormone that signals hunger. In the human portion of the study, 20 male participants who drank carbonated water (sweetened or unsweetened) had triple the blood levels of ghrelin compared to those who drank still water or degassed sparkling water.
The researchers concluded that carbon dioxide itself drove the increase in ghrelin production. While you might feel temporarily full from the gas expanding in your stomach, the hormonal response could push you to eat more afterward. That said, ghrelin’s role in actual overeating is complex, and a single hormone measurement doesn’t determine how much someone will eat at their next meal.
Hydration Compared to Still Water
One concern people sometimes have is whether the carbonation somehow makes sparkling water less hydrating. It doesn’t. A study that developed a beverage hydration index, measuring how much fluid your body retains two hours after drinking, found no difference in cumulative urine output between sparkling water and still water over four hours. Your body treats them the same way when it comes to hydration. If you prefer the taste of sparkling water and it helps you drink more fluids throughout the day, that’s a net positive for your digestion regardless of any other effects.
Who Benefits and Who Should Be Cautious
Carbonated water isn’t universally good or bad for digestion. It occupies a middle ground that depends on your specific situation:
- Constipation: Carbonated mineral water can increase bowel movement frequency and improve stool consistency, especially water that’s high in sulfate and magnesium.
- Swallowing problems: The sensory stimulation from fizz can help trigger a stronger swallowing reflex.
- Acid reflux: Carbonation significantly weakens the sphincter that prevents acid from entering the esophagus, potentially worsening symptoms.
- Bloating and gas: The CO2 produces real gas in your digestive tract, increasing belching and feelings of fullness.
- Appetite: Carbonation may raise levels of the hunger hormone ghrelin, potentially increasing appetite despite the temporary feeling of fullness.
For someone with no existing digestive complaints, sparkling water is a perfectly fine choice that hydrates just as well as still water. The digestive effects, both positive and negative, become more relevant when you’re already managing a specific condition.