Plain carbonated water contains zero calories, and no credible evidence links it to weight gain in humans. The bubbles come from dissolved carbon dioxide, which adds no energy to the drink. A handful of studies have explored whether carbonation might indirectly nudge your body toward gaining weight through hormonal or appetite changes, but when researchers actually measure how much people eat after drinking sparkling water, the calorie counts come out the same as with still water. The story gets more complicated when flavored sparkling waters, sweetened sodas, or artificially sweetened drinks enter the picture, and the distinction matters more than most people realize.
What Happens in Your Stomach After Sparkling Water
When you swallow carbonated water, the dissolved CO2 releases gas inside your stomach, physically expanding it. Imaging studies confirm this: gastric volume after drinking carbonated water is measurably larger than after flat water or a non-carbonated beverage.1PubMed Central. The role of a pre-load beverage on gastric volume and food intake: comparison between non-caloric carbonated and non-carbonated beverage That distension can trigger short-term feelings of fullness, which is why some people drink sparkling water before a meal hoping to eat less.
But the fullness does not translate into eating fewer calories. In the same study, when participants sat down to a meal after drinking carbonated water, flat flavored water, or plain still water, total calorie intake was virtually identical across all three groups, whether the meal was small or large.1PubMed Central. The role of a pre-load beverage on gastric volume and food intake: comparison between non-caloric carbonated and non-carbonated beverage A separate study looking at men and women who drank sparkling water at breakfast found the same thing: lunch intake was no different from conditions where they drank caloric beverages instead.2PubMed Central. Can carbonated water support weight loss? The stomach stretching from gas seems to fade quickly enough that your appetite catches up by the time real food arrives.
The Ghrelin Study That Sparked Concern
The most widely cited piece of evidence suggesting carbonated water could promote weight gain comes from a 2017 study conducted at Birzeit University. Researchers gave rats regular access to carbonated beverages and found that those rats had higher levels of ghrelin, a hormone that stimulates hunger, and ate more food than rats drinking flat versions of the same drinks. In a parallel experiment, 20 healthy young men who drank carbonated beverages also showed elevated ghrelin levels compared to when they drank still versions.3PubMed. Carbon dioxide in carbonated beverages induces ghrelin release and increased food consumption in male rats: Implications on the onset of obesity
This study generated headlines, but it has serious limitations that are worth understanding. The rat portion used sugar-sweetened carbonated drinks, not plain sparkling water, so it is hard to separate the effects of carbonation from the effects of sugar. The human portion measured ghrelin in only 20 people and did not actually track whether those men ate more food afterward. A rise in a hunger hormone is not the same as a rise in body weight, especially when multiple controlled feeding studies, described above, show that calorie intake does not change when carbonation is present. The finding remains interesting but isolated. No large human trial has confirmed that plain sparkling water leads to increased eating or weight gain over time.
Does Carbonation Change How Fast You Digest Food?
Another theory is that carbonated water might alter digestion in a way that promotes weight gain, perhaps by speeding up gastric emptying and making you hungry again sooner. The evidence here is reassuring. A study measuring both solid and liquid emptying from the stomach found that carbonated water did not change overall gastric emptying speed at all. What it did change was the distribution of food within the stomach: more of the meal sat in the upper portion of the stomach compared to flat water, likely because of gas-related distension. But the total time it took for the stomach to empty was the same either way.4PubMed. Effect of carbonated water on gastric emptying and intragastric meal distribution
Research on athletes during exercise tells the same story. When people drank carbonated versus flat water while working out at moderate intensity, gastric emptying rates were identical.5PubMed. Effects of drink carbonation on the gastric emptying characteristics of water and flavored water So carbonation does not appear to speed up or slow down digestion in a way that would meaningfully affect hunger timing or nutrient absorption.
Why the Type of Carbonated Drink Matters Enormously
Most of the confusion around carbonated water and weight gain comes from lumping all fizzy drinks together. A can of regular soda contains around 140 calories of sugar. A bottle of plain sparkling water contains zero. These are fundamentally different products that happen to share bubbles, and treating them as interchangeable is where popular advice goes sideways.
The weight-relevant evidence is strong on one point: replacing sugary drinks with water reduces calorie intake substantially. A study tracking beverage substitution patterns found that swapping all sweetened caloric beverages with plain water predicted a drop of about 200 calories per day over 12 months, and the body did not compensate by eating more food or drinking other caloric drinks to make up the difference.6PubMed. Replacing sweetened caloric beverages with drinking water is associated with lower energy intake That 200-calorie daily deficit is large enough to produce meaningful weight loss over time. Whether the replacement water is flat or carbonated is beside the point; what matters is removing the sugar.
If sparkling water helps you avoid soda or juice because you enjoy the fizz, the trade is overwhelmingly in your favor. The carbonation itself is metabolically inert. It is the calories that were in the old drink, not the bubbles in the new one, that determine the effect on your weight.
Artificially Sweetened Sparkling Drinks and Weight
Flavored sparkling waters and diet sodas occupy a middle ground that generates its own set of questions. Many flavored sparkling waters contain artificial or non-nutritive sweeteners (NNS) and zero calories. Whether those sweeteners affect weight has been debated for years, and the evidence is more favorable than the popular narrative suggests.
A year-long randomized trial assigned people who had already completed a weight-loss program to drink either water or NNS beverages. After 52 weeks, both groups maintained significant weight loss from baseline. The water group kept off about 6.1 kilograms on average, while the NNS beverage group kept off about 7.5 kilograms. The difference was statistically significant in favor of the sweetened drinks, not against them.7PubMed Central. Non-nutritive sweetened beverages versus water after a 52-week weight management programme: a randomised controlled trial One possible explanation is that people assigned to water-only felt more deprived and were less adherent to their overall diet, while those allowed NNS drinks found it easier to avoid caloric beverages.
This does not mean diet drinks are a weight-loss tool on their own. It suggests that for people already working on their diet, having a zero-calorie fizzy option available does not sabotage the effort and may actually make it easier to sustain. The broader point holds: the calories in a drink determine its weight effects. Bubbles alone do not add or subtract anything.
Does Drinking Water Itself Burn Calories?
You may have heard that drinking cold water boosts metabolism because your body has to warm it up. This is technically true in the sense that warming cold water from near-freezing to body temperature requires a small amount of energy. But “small” is the operative word. A study testing whether drinking cold water (cooled to about 3°C) increased energy expenditure found a bump of only about 4.5% over 60 minutes, and room-temperature distilled water produced no detectable increase at all.8The Journal of Clinical Endocrinology & Metabolism. Water-Induced Thermogenesis Reconsidered: The Effects of Osmolality and Water Temperature on Energy Expenditure after Drinking The researchers concluded that the effect was well below the theoretical energy cost of heating the water and that water is not a useful thermogenic agent for managing obesity.
A separate investigation comparing actual water drinking to a sham procedure (participants went through the motions of drinking without swallowing fluid) found that any small uptick in resting energy expenditure after drinking was not significantly different from the sham condition.9Nutrition & Diabetes. Water-induced thermogenesis and fat oxidation: a reassessment In other words, the act of drinking may itself cause tiny metabolic fluctuations unrelated to the water. If you are hoping that sparkling water’s extra coldness or CO2 somehow burns meaningful calories, the numbers do not support it.
Teeth and Bones
Weight aside, people who drink a lot of sparkling water often wonder about dental erosion and bone health. These concerns are worth addressing because they influence whether people stick with sparkling water as a substitute for other drinks.
For teeth, the distinction between plain sparkling water and flavored sparkling water matters quite a bit. Plain sparkling mineral water dissolves tooth enamel at rates roughly a hundred times lower than soft drinks, and de-gassing the water (removing the fizz) only slightly reduced its already-low erosive effect. Researchers concluded that carbonation itself is not an important factor in dental erosion and that mineral waters are a safe alternative to acidic beverages.10PubMed. Investigation of mineral waters and soft drinks in relation to dental erosion Flavored sparkling waters are another story. Testing showed that all flavored sparkling waters examined had low pH values (ranging from about 2.74 to 3.34) and erosive potential comparable to or greater than pure orange juice.11PubMed. The erosive potential of flavoured sparkling water drinks The citric acid and other flavorings, not the carbonation, drive the damage. If you care about enamel, stick to unflavored sparkling water or rinse your mouth after drinking flavored varieties.
For bones, the evidence is similarly reassuring. A study of older women found no association between carbonated beverage consumption and bone mineral density after adjusting for age, calcium intake, exercise, and other relevant factors. Modest intake of carbonated beverages did not appear to have adverse effects on bone density.12PubMed Central. Carbonated beverage consumption and bone mineral density among older women: the Rancho Bernardo Study The old worry about carbonation leaching calcium from bones has not held up to scrutiny. Some earlier observational studies linked cola specifically to lower bone density, but that association likely reflects the displacement of milk and other calcium-containing drinks rather than any direct effect of carbonation or phosphoric acid.
Bloating, Gas, and Comfort
Even if sparkling water does not affect your weight, it can affect how you feel. The gas released in your stomach has to go somewhere, and for many people that means belching, mild bloating, or a feeling of abdominal distension. For most people this is harmless and temporary. For people with irritable bowel syndrome or functional dyspepsia, the additional gas can aggravate symptoms and make carbonated water genuinely uncomfortable to drink in large quantities.
Some people find that the bloating discourages them from drinking enough fluid overall. If sparkling water makes you drink less total water throughout the day because you feel overly full, you are working against yourself. The practical move is to pay attention to how your body responds. If bloating is mild and you enjoy the bubbles, there is no metabolic reason to switch. If it is interfering with hydration or making you uncomfortable enough to avoid drinking, flat water is the better choice for you specifically.
Mineral Water and Blood Sugar
An interesting tangent in the sparkling-water research involves bicarbonate-rich mineral water, which is naturally carbonated from geological sources. A study examining this type of mineral water in the context of blood sugar management found that its consumption was associated with improved glycemic control and favorable shifts in gut bacteria composition, specifically an increase in bacterial populations linked to leanness.13PubMed Central. The Consumption of Bicarbonate-Rich Mineral Water Improves Glycemic Control The mechanism likely involves the dissolved minerals (bicarbonate, magnesium, calcium) rather than the carbonation per se, so this finding does not generalize to all sparkling water.
Still, it is a reminder that not all carbonated waters are chemically identical. Natural mineral waters contain dissolved solids that vary enormously depending on the source. Commercial sparkling water made by injecting CO2 into purified water has a very different mineral profile than water bottled from a volcanic spring. If you are choosing sparkling water partly for its mineral content, reading the label for bicarbonate, calcium, and magnesium levels gives you more useful information than just checking whether it is carbonated.
When Carbonated Water Could Work Against You
There are a few narrow scenarios where sparkling water could theoretically nudge things in the wrong direction, even without containing any calories. If carbonation makes you feel full enough to skip a nutrient-dense meal but hungry again an hour later (when you reach for a snack instead), the net effect on your diet could be negative. This is speculative, and no study has documented this pattern specifically for plain sparkling water, but it aligns with the broader principle that short-lived fullness signals do not reliably reduce total daily intake.
Another scenario involves people who associate fizzy drinks with food. If the sensory experience of bubbles triggers a learned desire for chips, pizza, or other foods you typically eat alongside soda, the switch to sparkling water could carry some of that association along. Behavioral researchers call this a conditioned cue. Whether it matters in practice depends entirely on the individual. For most people, the switch from soda to sparkling water disrupts the calorie intake, not the snacking behavior.
A review article in BMJ Nutrition, Prevention and Health evaluated the overall evidence and concluded that carbonated water is not a standalone solution for weight loss. A balanced diet and regular physical activity remain the fundamental components of sustainable weight management.2PubMed Central. Can carbonated water support weight loss? That is a sensible framing: sparkling water is not a magic bullet in either direction. It does not cause weight gain, and it does not cause weight loss. It is water with bubbles, and the bubbles are metabolically trivial.
What About Kids and Adolescents?
Parents often wonder whether letting children drink sparkling water will set them up for unhealthy habits or weight issues. No research has specifically shown that plain carbonated water causes weight gain in children. The concern pediatricians more often raise is about flavored or sweetened sparkling drinks being marketed as healthier alternatives to soda while still containing added sugars or acids. A child who drinks unflavored sparkling water instead of juice or soda is reducing calorie and sugar intake, full stop. A child who drinks a flavored sparkling water with 20 grams of sugar is drinking liquid candy with better branding.
The dental erosion question is more relevant for kids, whose enamel is still developing. Unflavored sparkling water poses minimal risk, as described earlier, but flavored varieties with citric acid are worth limiting for young teeth. The weight question, though, comes down to the same principle as for adults: check the nutrition label. If the drink has calories, those calories count. If it does not, the carbonation is irrelevant to weight.