🧪 Chemistry & Science

Carbonated Drinks and Gas: The Fizzy Truth About Bloating and Farts

That satisfying fizz in soda, sparkling water and beer is pure carbon dioxide—and once you swallow it, your digestive system has to deal with every last bubble. Here is the science of where it goes.

Where the Fizz Comes From

Carbonated drinks are made by forcing carbon dioxide (CO2) gas into liquid under pressure. Following Henry's law, the amount of gas that dissolves is proportional to the pressure above the liquid, which is why a sealed can holds far more CO2 than an open glass. A small fraction of the dissolved gas reacts with water to form carbonic acid, the mild tang you taste alongside the prickle of bursting bubbles. When you crack the seal, pressure drops and the liquid becomes supersaturated, so CO2 escapes as the familiar stream of bubbles nucleating on the glass. A typical 330-millilitre can contains roughly two to three grams of dissolved CO2—several hundred millilitres of gas at body temperature. All of that gas enters your mouth and stomach, and your body must route it somewhere, whether upward as a burp or downward through the gut.

Swallowed Air Versus Released Gas

Most of the gas from a fizzy drink never reaches your intestines. As the liquid warms in your stomach, dissolved CO2 rapidly comes out of solution and collects as a bubble at the top of the stomach, which the body usually vents as a burp—a process called eructation. This is the same mechanism as aerophagia, the swallowing of air, except the gas arrives pre-dissolved. However, drinking quickly, using a straw, or gulping while talking adds extra swallowed air, and some CO2 stays dissolved long enough to pass into the small intestine. There it can be partly absorbed into the blood and exhaled through the lungs, but a residual portion travels onward to the colon. Combined with gas produced by gut bacteria, this contributes to bloating, abdominal pressure and, eventually, flatulence released from the other end.

Why Some People Get More Bloated

Individuals respond very differently to carbonation. People with a sensitive or hypersensitive gut—such as those with irritable bowel syndrome—often perceive normal volumes of intestinal gas as painful bloating, even when they produce no more than anyone else. The drink's other ingredients matter too. Many sodas are sweetened with high-fructose corn syrup or contain fructose, a sugar that is poorly absorbed in large amounts and feeds gas-producing bacteria. Diet and sugar-free versions frequently use sugar alcohols like sorbitol, which are fermented in the colon and notorious for causing gas and loose stools. Cold temperature slows gastric emptying slightly, and drinking on an empty stomach speeds the gas into the intestine. Carbonated alcoholic drinks add yet another layer, since alcohol relaxes the lower oesophageal sphincter and can disturb normal gut motility.

Managing the Fizz

You do not have to give up sparkling drinks to stay comfortable. Drinking slowly and without a straw reduces the extra air you swallow, and pausing to let a freshly poured glass settle lets some CO2 escape before it reaches your stomach. Letting a drink go partly flat, or stirring it, removes a meaningful share of the gas. Choosing beverages sweetened with ordinary sugar rather than sorbitol or large doses of fructose can spare sensitive guts. If bloating is persistent, switching from soda to still water for part of the day is the simplest fix. Gentle movement after a meal helps gas move through and exit naturally rather than accumulating. For most people, carbonation causes harmless, temporary bloating—but frequent severe discomfort, pain or a change in bowel habits is worth discussing with a doctor.

Did You Know?

Fun Fact

Astronauts cannot easily burp in microgravity, because without gravity the gas does not separate from liquid in the stomach—so carbonated drinks are essentially banned in space to avoid an unpleasant 'wet burp.'

Sources

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