Carbonated drinks affect your body in a cascade of ways that starts the moment you take a sip and extends to your bones, blood vessels, liver, and teeth over the long term. The carbon dioxide gas that gives these beverages their fizz triggers immediate changes in your stomach and esophagus, while the sugar, acids, and additives that ride along in most sodas carry a separate and often more serious set of consequences. The distinction between plain sparkling water and a cola loaded with high-fructose corn syrup matters enormously here, because the carbonation itself is only one piece of the story.
What Happens in Your Stomach and Esophagus
When you drink something carbonated, dissolved carbon dioxide rapidly converts to gas once it hits the warm, acidic environment of your stomach. That burst of gas inflates the upper portion of the stomach, a sensation most people recognize as bloating or the urge to burp. Research using imaging to track how a meal moves through the stomach found that carbonated water didn’t change how fast the stomach emptied overall, but it did significantly alter where food sat inside it. With carbonated water, a much larger share of both solids and liquids stayed pooled in the upper stomach compared to still water, likely because the gas stretched that region and slowed its contractions.1PubMed. Effect of carbonated water on gastric emptying and intragastric meal distribution Magnetic resonance imaging studies have measured gastric gas volumes around 600 milliliters after drinking a carbonated cola, which is enough to cause noticeable stomach discomfort in many people.
Below the stomach, the lower esophageal sphincter, a ring of muscle that keeps stomach contents from washing back up, takes a direct hit from carbonation. One study found that all carbonated beverages tested produced a sustained drop of 30 to 50 percent in the strength of that sphincter over 20 minutes, and in roughly six out of ten cases the weakening was severe enough to reach levels normally considered diagnostic of an incompetent sphincter. Tap water caused no such reduction.2Journal of Gastrointestinal Surgery. Response of the Lower Esophageal Sphincter to Gastric Distention by Carbonated Beverages A separate trial in healthy volunteers confirmed this: after a carbonated drink, the sphincter’s resting pressure dropped by more than half compared to baseline, and the frequency of transient sphincter relaxations spiked dramatically.3PubMed. Ingestion of a carbonated beverage decreases lower esophageal sphincter pressure and increases frequency of transient lower esophageal sphincter relaxation in normal subjects A systematic review of the broader evidence echoed these findings, noting that carbonated beverages may lead to a transient reduction in sphincter pressure.4PubMed. Systematic review: the effects of carbonated beverages on gastro-oesophageal reflux disease
If you already deal with acid reflux or heartburn, this is the mechanism that should concern you most. A weakened esophageal sphincter makes it easier for stomach acid to creep upward, and the gas pressure from carbonation adds a physical push. That doesn’t mean every fizzy drink will give you reflux, but if you’re prone to it, carbonated beverages are working against you on two fronts at once.
Your Teeth and the Acid Question
Every carbonated drink is acidic. The carbonation process itself creates carbonic acid, which gives even plain sparkling water a pH lower than tap water. Most flavored sodas go further, adding citric acid or phosphoric acid that push the pH well below the threshold where tooth enamel begins to dissolve. In vitro research on enamel erosion has shown that low pH and high citrate content cause more surface enamel loss.5Journal of the Formosan Medical Association. Erosive potential of soft drinks on human enamel: An in vitro study
Plain carbonated water is much less damaging than cola or citrus soda, but it’s not completely neutral. A study testing carbonated water on enamel found that microhardness decreased significantly in most experimental groups compared to untreated enamel, and scanning electron microscopy revealed visible surface destruction. One exception was low-level carbonated water that contained added calcium ions, which appeared to buffer the erosive effect.6PubMed Central. Effect of carbonated water manufactured by a soda carbonator on etched or sealed enamel The practical takeaway is that plain sparkling water is a minor concern for healthy enamel, but if you already have enamel erosion or exposed dentin from orthodontic treatment, even unflavored carbonated water can make things slightly worse. The real erosion culprits are flavored sodas, energy drinks, and citrus-based sparkling beverages where the combination of carbonation, citric acid, and sugar creates a triple assault on your teeth.
Sugar-Sweetened Sodas and Metabolic Damage
The sugar in regular soda is where the most consequential long-term health effects live. A typical 12-ounce can of soda contains around 39 grams of sugar, most of it from high-fructose corn syrup. Fructose is processed almost exclusively by the liver, and in the quantities delivered by daily soda consumption, it ramps up the liver’s fat-producing machinery. Research has linked regular soft drink consumption to nonalcoholic fatty liver disease through precisely this pathway: fructose increases fat synthesis in the liver, gradually leading to fat accumulation that can progress to inflammation and scarring.7PubMed Central. Soft drinks consumption and nonalcoholic fatty liver disease Beverages sweetened with high-fructose corn syrup have been specifically tied to metabolic abnormalities and fatty liver development in human trials, and ingested carbohydrates in general appear to drive liver fat accumulation more directly than dietary fat does.8PubMed Central. Carbohydrate intake and nonalcoholic fatty liver disease: fructose as a weapon of mass destruction
The metabolic fallout extends beyond the liver. A prospective study following participants over several years found that those who drank the most sugar-sweetened beverages, roughly six or more servings per week, had a 46 percent higher risk of developing prediabetes compared to people who didn’t drink them at all. The association held even after adjusting for body weight, meaning the effect wasn’t simply because soda drinkers weighed more. Insulin resistance, measured directly, also worsened in a dose-dependent fashion with greater soda consumption.9PubMed Central. Sugar-Sweetened Beverage but Not Diet Soda Consumption Is Positively Associated with Progression of Insulin Resistance and Prediabetes A seven-year study of middle-aged men showed a similar trend: those drinking one or more servings of sugar-sweetened beverages per day had higher diabetes incidence rates than rare or never consumers.10PubMed. Sugar-sweetened beverage and diet soda consumption and the 7-year risk for type 2 diabetes mellitus in middle-aged Japanese men
What Soda Does to Your Blood Vessels
Sugar-sweetened beverages also take a measurable toll on blood vessel function within hours of drinking them. In a controlled study comparing sugary drinks to water, soda consumption impaired both the tiny blood vessels in the skin and the larger arteries in the arm. The vascular response to a chemical that normally relaxes blood vessels dropped significantly after a sugary drink, and the arteries’ ability to dilate in response to increased blood flow was also reduced. The researchers attributed this to a surge in oxidative stress that depleted nitric oxide, the molecule your blood vessels depend on to stay flexible and open.11PubMed. Effects of Sugar-Sweetened Beverage Consumption on Microvascular and Macrovascular Function in a Healthy Population
The encouraging news is that this damage appears to be at least partly reversible in real time. A follow-up experiment showed that the dip in microvascular function triggered by a sugary drink was significantly blunted when participants did 30 minutes of aerobic exercise around the same time.12Microvascular Research. Transient endothelial dysfunction induced by sugar-sweetened beverage consumption may be attenuated by a single bout of aerobic exercise That doesn’t make soda harmless, but it does suggest that physical activity provides a partial buffer against the acute vascular insult. The concern is more about what happens when these small insults accumulate day after day in someone who drinks soda regularly and doesn’t exercise enough to compensate.
The Cola and Bone Density Link
One of the more persistent fears about carbonated drinks is that they leach calcium from your bones. The evidence for this is narrower than the headline suggests. Data from the Framingham Osteoporosis Study, which looked at bone mineral density across more than 2,500 people, found that cola intake was associated with significantly lower bone density at the hip in women but not in men. Women who drank cola daily had roughly 3.7 percent lower bone density at the femoral neck and 5.4 percent lower at another hip measurement site compared to women who rarely drank cola. Diet cola and decaffeinated cola showed similar patterns, though the effect was weaker for decaf. Crucially, noncola carbonated beverages showed no significant association with bone density at all.13PubMed. Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study
This is one of the clearest examples of why lumping all fizzy drinks together is misleading. The carbonation itself doesn’t appear to be the problem. The working theory is that cola’s phosphoric acid, which other carbonated beverages don’t contain, may interfere with calcium balance. Another possibility is displacement: people who drink a lot of cola tend to drink less milk, and over years that substitution alone could erode bone density. If you drink sparkling water or non-cola flavored seltzers, this particular concern doesn’t apply to you.
Kidneys and Cola
Your kidneys filter everything you drink, and cola appears to be uniquely problematic here as well. An epidemiological study found that people who drank two or more colas per day had an adjusted odds ratio of about 2.3 for chronic kidney disease compared to people who didn’t drink cola. The association held for both regular and artificially sweetened colas. Noncola carbonated beverages, by contrast, showed no increased risk at all, with an odds ratio of 0.94.14PubMed Central. Carbonated Beverages and Chronic Kidney Disease Again, the carbonation itself appears innocent; it’s the specific cocktail of ingredients in cola, likely the phosphoric acid, that seems to drive the association. This is an observational finding, so it can’t prove causation on its own, but the specificity of the cola link and the absence of risk from other carbonated drinks is a pattern worth paying attention to.
Does Carbonation Make You Hungrier?
Here the evidence is genuinely conflicting, which is unusual for a question that seems so straightforward. One study found that carbonated beverages increased levels of ghrelin, the so-called hunger hormone, in both rats and a small group of 20 healthy men, and the rats that drank carbonated beverages ate more food.15PubMed. Carbon dioxide in carbonated beverages induces ghrelin release and increased food consumption in male rats: Implications on the onset of obesity That result got a lot of media attention when it was published, because it implied that even zero-calorie sparkling water could make you gain weight by stoking appetite.
But another study found the opposite. When researchers compared a non-caloric carbonated drink, a non-caloric still drink, and water in terms of their effects on stomach volume and subsequent food intake, the carbonated version actually suppressed ghrelin more effectively during the period after eating. The area under the ghrelin curve was roughly half as large after the carbonated drink compared to the still version or water during a standardized meal.16PubMed Central. The role of a pre-load beverage on gastric volume and food intake: comparison between non-caloric carbonated and non-carbonated beverage The contradiction likely comes down to timing and context: carbonation on an empty stomach may behave differently from carbonation consumed alongside food, and stomach distension from gas can temporarily reduce appetite even if ghrelin rises. In practical terms, the effect is probably small enough that you shouldn’t rely on sparkling water as an appetite suppressant or fear it as an appetite stimulant.
Diet Sodas and Artificial Sweeteners
Switching to diet soda removes the sugar problem but introduces a different set of open questions. A high-profile study in mice and a small group of humans found that commonly used non-nutritive sweeteners altered the composition of gut bacteria and drove glucose intolerance, an effect that could be transferred to germ-free mice through fecal transplant of the microbiota from sweetener-consuming animals.17Nature. Artificial sweeteners induce glucose intolerance by altering the gut microbiota That paper raised alarm, but the broader literature is less decisive. A 2023 review of the field noted that while some human trials observed changes to gut microbiota from non-nutritive sweeteners, many other randomized controlled trials found no significant impact.18PubMed Central. Effect of Non-Nutritive Sweeteners on the Gut Microbiota
There’s also evidence that diet soda changes how your brain processes sweet taste. Neuroimaging studies have found that habitual diet soda drinkers show greater activation in dopamine-related brain regions when tasting any sweet substance, and they lose the ability to distinguish between real sugar and artificial sweeteners in terms of brain response. More striking, heavier diet soda consumption was associated with reduced activity in the caudate head, a reward-processing region, when tasting saccharin, suggesting a kind of blunted reward response that might drive people to seek more sweetness.19Physiology & Behavior. Altered processing of sweet taste in the brain of diet soda drinkers A broader review confirmed that non-nutritive sweeteners elicit different neuronal responses in reward and satiation areas compared to caloric sweeteners, though the downstream effects on actual eating behavior remain unclear.20PubMed. Effects of Non-nutritive Sweeteners on Sweet Taste Processing and Neuroendocrine Regulation of Eating Behavior
On the metabolic side, the prospective study that found a 46 percent increased prediabetes risk from sugar-sweetened beverages found no such association for diet soda. Neither prediabetes incidence nor insulin resistance tracked with diet soda intake.9PubMed Central. Sugar-Sweetened Beverage but Not Diet Soda Consumption Is Positively Associated with Progression of Insulin Resistance and Prediabetes That’s reassuring, but it doesn’t mean diet soda is metabolically inert. The honest summary is that diet soda avoids the clearest harms of sugar-sweetened soda while introducing subtler, less-understood effects on gut bacteria, brain reward circuitry, and possibly appetite regulation. The evidence isn’t strong enough to say diet soda is dangerous, but it’s not clean enough to call it harmless either.
Carbonated Water and Blood Pressure
Some sparkling mineral waters contain quite a bit of sodium, which raises an obvious concern about blood pressure. The evidence here is more reassuring than you might expect. A study of sodium-rich carbonated mineral water found no differences in blood pressure between participants drinking the mineral water and those drinking low-sodium water, and no change from baseline values.21PubMed. Sodium-rich carbonated natural mineral water ingestion and blood pressure A randomized controlled trial specifically testing a high-sodium, bicarbonate-rich sparkling water confirmed that blood pressure changes did not differ between groups, and this held true for both people with normal blood pressure and those with hypertension. Urinary sodium excretion, which went up as expected, showed no association with blood pressure increases.22PubMed. Blood Pressure Stability and Plasma Aldosterone Reduction: The Effects of a Sodium and Bicarbonate-Rich Water – A Randomized Controlled Intervention Study The bicarbonate in mineral water may partly explain this: sodium bicarbonate appears to behave differently in the body than sodium chloride when it comes to blood pressure effects. If you drink sparkling mineral water and worry about the sodium content on the label, these studies suggest the concern is overblown.
Caramel Coloring and 4-MEI
Beyond sugar and acid, some carbonated drinks carry additives with their own health concerns. The caramel coloring used in colas and certain other dark-colored soft drinks can contain 4-methylimidazole, a chemical formed during the manufacturing of certain types of caramel color. A quantitative risk assessment of 12 popular soft drinks found wide variation in 4-MEI levels. The highest concentrations, over 900 micrograms per liter, appeared in one brand, while Coca-Cola had the lowest at under 12 micrograms per liter. At routine consumption levels, some of these beverages pushed daily 4-MEI exposure above 29 micrograms, the threshold at which California’s Proposition 65 requires a warning label.23PubMed Central. Caramel color in soft drinks and exposure to 4-methylimidazole: a quantitative risk assessment The cancer risk from 4-MEI at these levels is small on an individual basis, but across a population of millions of daily soda drinkers, even tiny per-person risks translate to meaningful numbers. Clear or uncolored carbonated drinks sidestep this issue entirely.
Sparkling Water Versus Soda
Running through all of these effects, a consistent theme emerges: the carbonation itself is the least of your worries. Plain sparkling water weakens the esophageal sphincter temporarily, produces bloating, and is mildly more erosive to enamel than still water. Those are real effects, but they’re transient and modest. The serious, accumulating damage comes from the ingredients that hitch a ride on the bubbles. Sugar-sweetened sodas carry well-documented risks to your liver, blood sugar regulation, blood vessels, and probably your kidneys. Cola specifically adds phosphoric acid to the equation, which is linked to lower bone density and higher kidney disease risk in ways that other carbonated beverages are not. Diet sodas remove the sugar but introduce open questions about gut bacteria and brain reward processing that science hasn’t fully resolved.
If you enjoy the fizz but want to minimize risk, plain carbonated water or mineral water is in a fundamentally different category from cola or sweetened soda. The most useful thing you can do with the evidence is stop thinking about “carbonated drinks” as a single category and start thinking about what’s dissolved in the water alongside the carbon dioxide. That’s where the real action is.