Can Soda Give You Diarrhea? And Why It Happens

Soda can absolutely give you diarrhea, and it often does so through several mechanisms working at once. The combination of high sugar or artificial sweeteners, caffeine, carbonation, and acidic additives creates a cocktail that your gut may struggle to handle, especially in larger quantities. Which ingredient is the primary culprit depends on the type of soda and your individual digestive system, but the sugar content alone is enough to cause loose stools in many people.

How Sugar Overwhelms Your Gut

The most common reason regular soda triggers diarrhea comes down to sugar, specifically fructose. Most mainstream sodas are sweetened with high-fructose corn syrup, which delivers a large dose of fructose in a single serving. Your small intestine absorbs fructose through a specific transporter protein called GLUT5, which works by passive diffusion rather than active pumping.¹ That transporter has a limited capacity. When you drink a can or two of soda and flood the intestine with more fructose than GLUT5 can handle, the unabsorbed sugar stays in the gut lumen.

Unabsorbed fructose pulls water into the intestine through osmosis. The gut essentially becomes waterlogged, and that excess fluid speeds up transit and produces loose, watery stools. Bacteria in the colon also ferment the leftover sugar, producing gas, bloating, and organic acids that further irritate the bowel. This is a form of osmotic diarrhea, and it doesn’t damage the intestinal lining; it’s a mechanical consequence of too much unabsorbed solute sitting in the wrong place.²

The threshold where this happens varies a lot from person to person. Some people can absorb fructose efficiently; others hit their limit with as little as 25 grams, roughly the amount in a single 12-ounce can of soda. Drinking soda on an empty stomach makes it worse because there’s no food to slow gastric emptying and spread out absorption over time. Two cans in quick succession on a hot afternoon is a classic recipe for a bathroom emergency.

Diet Soda Has Its Own Problems

Switching to diet soda doesn’t necessarily spare your gut. Artificial sweeteners and sugar alcohols interact with the digestive system in ways that can be just as disruptive as sugar, sometimes more so. Sugar alcohols like xylitol, sorbitol, and erythritol are poorly absorbed in the small intestine by design. When they reach the colon, they draw water in and get fermented by bacteria, producing the same osmotic diarrhea and gas that excess fructose causes.³ The severity depends on the specific sweetener, the dose, and whether your body has had time to adjust. People who regularly consume sugar alcohols tend to tolerate them better over time, likely because their gut bacteria adapt.

Non-caloric sweeteners like sucralose, aspartame, acesulfame potassium, and saccharin work through a different pathway. Rather than causing osmotic diarrhea directly, these sweeteners can increase the secretion of gut hormones that regulate intestinal motility, effectively speeding up how fast things move through your digestive tract.⁴ The evidence for this in humans is still limited, and most data comes from animal studies, so it’s fair to say the clinical relevance isn’t fully settled.⁵ But the anecdotal reports are consistent enough that if diet soda reliably gives you loose stools, the sweetener is a strong suspect.

There’s also emerging research on what these sweeteners do to your gut microbiome. Animal studies have found that sucralose can reduce populations of beneficial bacteria that produce butyrate, a short-chain fatty acid important for gut health, and trigger low-grade intestinal inflammation.⁶ Whether this translates directly to diarrhea symptoms in humans is unclear, but it suggests that chronic diet soda consumption could shift the gut environment in ways that make digestive symptoms more likely over time.

Caffeine Speeds Things Up

Caffeinated sodas add another layer. Coffee is well known for its laxative effect, and caffeine is one of the reasons why, though not the only one. In soda, caffeine stimulates the secretion of gastric acid and promotes colonic motility, meaning it makes the muscles of the large intestine contract more frequently and forcefully.⁷ A typical caffeinated cola contains around 30-45 milligrams of caffeine per can, which is modest compared to coffee. But if you’re drinking several over the course of a day, the cumulative caffeine adds up. And because the caffeine arrives alongside sugar, carbonation, and acids, each ingredient amplifies the others’ effects on gut motility.

People who are caffeine-sensitive tend to feel this more acutely. If you’ve noticed that even small amounts of coffee send you to the bathroom, caffeinated soda will do the same thing on a milder scale. The effect is also dose-dependent and varies with tolerance. Someone who drinks caffeine daily may hardly notice, while someone who rarely does might find that a single cola on an empty stomach causes urgency within an hour.

What Carbonation and Phosphate Additives Do

Carbonation itself is often blamed for soda-related digestive trouble, but its role is more nuanced than people assume. A study comparing carbonated and still water with a meal found that carbonation did not change the overall speed of gastric emptying. What it did do was shift where the food sat within the stomach, pushing a larger proportion into the upper portion.⁸ That redistribution can increase feelings of bloating and fullness, but it isn’t by itself a direct cause of diarrhea. The carbon dioxide gas that produces the bubbles is mostly released as belching; relatively little makes it far enough down the tract to cause lower intestinal distress.

The phosphate additives in cola-type drinks are a different story. Phosphoric acid gives cola its tangy bite, and phosphate-based additives are used in many processed foods and beverages. In a study of healthy adults, introducing foods with phosphate additives caused intestinal distress, soft stools, and mild diarrhea. Most subjects adapted within the experimental period, but some experienced intermittent symptoms throughout.⁹ Cola drinkers who notice their symptoms are worse with Coke or Pepsi than with clear lemon-lime sodas might be reacting to these phosphate compounds on top of the sugar.

Why Kids Are Especially Vulnerable

Children, particularly toddlers, are much more susceptible to soda-related diarrhea than adults. A condition called “toddler’s diarrhea” or chronic nonspecific diarrhea of childhood has been directly linked to sugary beverage consumption. The evidence is strong: systematic reviews have found that beverages with a high fructose-to-glucose ratio, like apple and pear juice, are the worst offenders, but any sugar-sweetened drink can contribute. In one trial, infants consuming apple juice had roughly 80 percent higher fecal output and nearly double the duration of diarrhea compared to those given water.¹⁰

The mechanism is the same fructose malabsorption that affects adults, but children have less absorptive capacity in their smaller intestines. Breath hydrogen testing has confirmed carbohydrate malabsorption as the underlying issue, and the practical finding is straightforward: restricting or eliminating sugary drinks resolves the diarrhea in most cases without any other intervention.¹¹ While these studies focused primarily on juice, soda delivers the same or higher sugar loads, often with the additional burden of caffeine and acids. A toddler with persistent loose stools whose diet includes any significant amount of soda, juice, or sweetened drinks should have those drinks cut first before any other workup is considered.

If You Already Have a Sensitive Gut

People with irritable bowel syndrome, functional dyspepsia, or gastroesophageal reflux disease are playing with a shorter fuse. A narrative review of fluid intake and functional gastrointestinal disorders found that higher intakes of soft drinks, carbonated beverages, caffeinated drinks, and fruit juice are all associated with worsened symptoms in these conditions.¹² For someone with IBS-D (the diarrhea-predominant type), a single can of regular soda can be enough to trigger a flare, because the underlying gut is already hypersensitive to distension, osmotic changes, and motility shifts.

The low-FODMAP diet, commonly recommended for IBS management, specifically restricts excess fructose for this reason. High-fructose corn syrup is a high-FODMAP ingredient, which means that regular soda lands squarely on the “avoid” list for anyone following that approach. Diet soda may or may not be tolerated depending on the specific sweetener used. Sugar alcohols like sorbitol and mannitol are classified as polyols, another FODMAP category, which makes certain diet drinks problematic as well.

Soda Is a Terrible Rehydration Drink

One of the most persistent and harmful myths about soda is that flat ginger ale or cola can help when you have a stomach bug. In reality, soda makes dehydration worse, not better. Animal research has shown that rehydrating with a soft-drink-like sugar solution after dehydration resulted in greater dehydration and worse kidney injury compared to water or a stevia-sweetened alternative, despite the soda group drinking more total fluid.¹³ The high sugar concentration in soda creates an osmotic gradient in the gut that pulls water out of the body rather than helping absorb it.

Proper oral rehydration solutions work on the principle that sodium and glucose together activate a cotransporter in the intestinal lining that pulls water along with them.¹⁴ Soda has far too much sugar and almost no sodium, so it doesn’t activate this mechanism effectively. If you’re already dealing with diarrhea from any cause, drinking soda to rehydrate is likely to make the diarrhea worse while also worsening the dehydration. Water, diluted broth, or a commercial oral rehydration solution are far better choices.

Does Drinking It Cold Make Things Worse?

Most people drink soda chilled or over ice, and there’s a common belief that cold drinks are harder on the stomach. There’s a grain of truth here, though the picture is more complicated than “cold equals bad.” Research comparing water at different temperatures found that very cold water (around 2°C, or about 36°F) significantly reduced the frequency of stomach contractions for up to an hour compared to warm water.¹⁵ Slower gastric contractions mean the stomach empties differently, and in some people this altered pattern can contribute to discomfort.

The connection to diarrhea is indirect. Cold soda slowing stomach motility could theoretically cause a larger bolus of sugary liquid to arrive in the small intestine at once when the stomach finally does empty, overwhelming absorption capacity. But the temperature effect alone isn’t a major diarrhea trigger for most people. It’s the contents of the drink that matter far more than the temperature. If anything, sipping a soda slowly at room temperature gives your gut marginally more time to handle the sugar load, but it won’t eliminate the problem if you’re drinking quantities beyond your absorptive threshold.

When Soda-Related Diarrhea Becomes a Pattern

An occasional episode of loose stools after drinking too much soda is unpleasant but not a medical concern. It becomes worth investigating if you notice that even small amounts of soda (or other sugary drinks, fruit juices, or foods sweetened with high-fructose corn syrup) consistently cause diarrhea. That pattern could indicate fructose malabsorption, a condition that exists on a spectrum. Some people are inefficient fructose absorbers at baseline, and any significant fructose load exceeds their capacity.

Hydrogen breath testing is the standard diagnostic tool for this. You drink a measured fructose solution, and a clinician measures the hydrogen gas in your breath over the following hours. Elevated hydrogen levels indicate that fructose is reaching the colon unabsorbed, where bacteria ferment it and release hydrogen.¹⁶ The same test can be done with lactose to check for lactose malabsorption, or with glucose or lactulose to screen for small intestinal bacterial overgrowth, both of which can compound the problem. If you’re reacting to soda but also to bread, beans, onions, and fruit, the issue might be broader than just fructose, and a gastroenterologist can help sort through the possibilities.

Practical Steps to Reduce the Problem

If you enjoy soda but want to minimize the digestive fallout, a few adjustments can help:

• Drink less per sitting: Splitting a can across an hour gives your gut more time to absorb the sugar load than chugging it all at once.
• Pair soda with food: Eating alongside a carbonated drink slows gastric emptying and spreads sugar absorption over a longer window, reducing the osmotic hit to the small intestine.
• Watch for caffeine stacking: If you’re also drinking coffee or tea during the day, a caffeinated soda on top may push your total caffeine intake into the range that triggers colonic motility issues.
• Try different sweeteners: If diet soda is the trigger, the specific artificial sweetener matters. Erythritol tends to be better tolerated than sorbitol or xylitol because more of it gets absorbed in the small intestine before reaching the colon.
• Switch to cane sugar or sucrose-sweetened soda: Sucrose is broken down into equal parts glucose and fructose, and the presence of glucose actually helps fructose absorption. Sodas made with high-fructose corn syrup deliver excess free fructose without the glucose boost, making malabsorption more likely.

None of these steps eliminate the risk entirely if you’re a heavy soda drinker. The blunt reality is that the human gut did not evolve to process the concentration of sugars, sweeteners, acids, and stimulants found in modern soda. The occasional can is unlikely to cause trouble for most adults. Regular consumption of multiple servings a day, particularly on an empty stomach, is a reliable recipe for chronic loose stools and the bloating, cramps, and gas that go with them.

The Gut Microbiome Angle

Beyond the immediate osmotic and motility effects, there’s growing interest in how habitual soda consumption reshapes the gut microbiome in ways that could independently contribute to digestive symptoms. The sucralose study mentioned earlier found reductions in butyrate-producing bacteria and lower levels of butyrate itself in the gut.⁶ Butyrate is the primary energy source for the cells lining the colon, and low butyrate levels are associated with increased intestinal permeability and inflammation. If chronic diet soda consumption gradually depletes these beneficial bacteria, the gut lining could become less resilient, more prone to inflammation, and more reactive to other dietary triggers.

This research is still in its early stages, and almost all the direct evidence comes from animal models. Translating rodent microbiome findings to humans is notoriously tricky because the bacterial populations differ and humans have far more varied diets. Still, the direction of the evidence is consistent enough to be worth noting. If you find that your gut tolerance for various foods seems to be declining over time, and you’re also a daily diet soda drinker, the two things may not be coincidental. Reducing intake for a few weeks and tracking symptoms is a low-risk way to test the connection.