Carbonated drinks affect nearly every part of your digestive tract, starting the moment they hit your tongue. Whether you’re sipping plain sparkling water or a sugary cola, the carbon dioxide gas dissolved in the liquid triggers a chain of reactions in your mouth, stomach, esophagus, and beyond. The specific effects depend heavily on what else is in the drink: sugar, phosphoric acid, and artificial sweeteners each bring their own set of consequences.
What Happens in Your Stomach
When you drink a carbonated beverage on an empty stomach, the liquid passes quickly into the upper small intestine, where dissolved carbon dioxide converts to bicarbonate or escapes as gas. This creates a buildup of pressure in the gut. At volumes above about 300 milliliters (roughly 10 ounces), that pressure alone can produce a feeling of fullness, which is why sparkling water sometimes feels more filling than still water.
The carbonation also activates nerve pathways that change how your upper digestive tract moves. Specifically, the fizz stimulates nerves on your tongue that signal to your brainstem, which in turn adjusts the muscular contractions of your stomach and esophagus. For some people, this means carbonated water can actually help relieve indigestion or constipation. For others, it means bloating, gas, and discomfort.
Carbonation and Acid Reflux
If you deal with heartburn or gastroesophageal reflux, carbonated drinks are worth watching. The muscle at the bottom of your esophagus acts like a one-way valve, keeping stomach acid from traveling upward. Carbonation weakens that valve. In a study of reflux patients, drinking just 200 milliliters of a carbonated beverage dropped the resting pressure of that valve from about 24 mmHg to around 14 mmHg, a significant decrease compared to drinking the same volume of plain water.
On top of that, carbonation increased the number of times the valve temporarily relaxed on its own, and those relaxations lasted longer. Each one is an opportunity for acid to splash into the esophagus. Nine out of eleven patients in the study experienced these spontaneous relaxations after a carbonated drink, compared to six after water. If reflux is already a problem for you, this is one of the clearest ways carbonation can make things worse.
Effects on Your Teeth
Any carbonated drink is more acidic than plain water. The carbon dioxide reacts with water to form carbonic acid, which lowers the pH and can soften tooth enamel over time. Plain sparkling water is mildly acidic and poses minimal risk for most people, but citrus-flavored sparkling waters are a different story. The added citric acid pushes the acidity higher, increasing the potential for enamel erosion with regular exposure.
Sugary sodas compound the problem. Bacteria in your mouth feed on sugar and produce their own acid as a byproduct, so you get a double hit. Sipping a soda slowly over an extended period keeps your teeth bathed in acid for longer, which is more damaging than finishing the same drink quickly.
Sugar-Sweetened Sodas and Metabolic Health
The most significant health effects of carbonated drinks come not from the bubbles but from what’s dissolved alongside them. A regular sugar-sweetened soda causes a rapid spike in both blood sugar and insulin within 30 minutes of drinking it. Over time, this repeated cycle contributes to insulin resistance, weight gain, and type 2 diabetes risk.
There’s also an interesting effect on hunger. A study at Birzeit University found that carbon dioxide itself may stimulate the release of ghrelin, the hormone that signals hunger. In both rats and a parallel group of 20 healthy human males, drinking carbonated beverages raised ghrelin levels compared to flat alternatives. This could mean that carbonated drinks, even without sugar, nudge you toward eating more.
Diet sodas sweetened with sucralose or aspartame, on the other hand, don’t appear to trigger the same blood sugar or insulin response. In a study of healthy men who drank 20 ounces of artificially sweetened soda, blood glucose and insulin levels stayed flat over a two-hour window, essentially identical to baseline. Whatever long-term concerns exist around artificial sweeteners, an acute metabolic spike isn’t one of them.
Bone Density and Cola Specifically
You may have heard that carbonated drinks weaken your bones. The evidence here points specifically at cola, not carbonation in general. Cola contains phosphoric acid, which may interfere with calcium absorption and contribute to hormonal shifts that pull calcium out of bones. At least two studies have found a negative association between cola consumption and bone mineral density in women and adolescent girls. Animal studies have confirmed that high dietary phosphorus can cause bone loss.
That said, the picture isn’t entirely clear. Some researchers argue that the real issue is displacement: people who drink a lot of soda tend to drink less milk, so they simply get less calcium in their diet. Whether the phosphoric acid itself is the problem or the missing calcium is the problem remains debated. Either way, non-cola sparkling waters don’t contain phosphoric acid and haven’t been linked to bone loss.
Kidney Health Over Time
Heavy consumption of sugar-sweetened carbonated drinks is associated with chronic kidney disease. A large study published in Frontiers in Nutrition found that people drinking more than one serving per day of sugary beverages had a 45% higher risk of developing chronic kidney disease compared to non-drinkers. The connection appears to run partly through metabolic syndrome, the cluster of conditions including high blood pressure, high blood sugar, and excess abdominal fat that damages kidney function over years.
Hydration: Sparkling vs. Still Water
One common worry you can set aside: plain sparkling water hydrates you just as well as still water. A study that ranked 13 beverages by their hydration index, which measures how much urine your body produces after drinking them, found no meaningful difference between carbonated and flat water. The bubbles don’t pull water out of your system or act as a diuretic. If you prefer the fizz, it counts fully toward your daily fluid intake.
Who Should Be Cautious
The carbonation itself is relatively harmless for most people. Plain sparkling water is a reasonable substitute for still water, with the caveats that it can worsen reflux symptoms and cause bloating if you drink large amounts. The real concerns stack up around what comes with the carbonation. Sugar-sweetened sodas carry well-documented risks for metabolic health, kidney function, and dental erosion. Cola’s phosphoric acid adds a bone density concern on top of that. If you’re choosing between a plain seltzer and a sugary soda, your body will handle them very differently, even though both start with the same bubbles.