Carbonation is simply dissolved carbon dioxide gas, responsible for the characteristic bubbles in beverages like sodas, sparkling water, and seltzers. While plain carbonated water is often viewed differently than high-sugar sodas, the physical presence of the gas introduces unique challenges for an athlete’s body. The central issue is not a specific chemical reaction but rather the mechanical and physiological consequences of introducing gas and certain additives into the digestive system, especially when combined with the physical stress of running. This distinction between the bubbles and the liquid’s contents is the primary consideration for a runner deciding what to drink.
The Primary Concern: Gastrointestinal Discomfort
The most immediate and noticeable effect of drinking carbonated beverages while running is the potential for gastrointestinal (GI) distress. This discomfort stems directly from the dissolved carbon dioxide gas. When a carbonated drink is consumed, the gas is released within the warm environment of the stomach, causing it to physically distend or expand. This rapid expansion creates a sensation of fullness or bloating and triggers the need to belch to release the built-up gas.
When the stomach is distended, especially coupled with the mechanical jostling that occurs with every stride a runner takes, it can lead to cramping, side stitches, and acid reflux. Running requires blood flow to be prioritized for working muscles, pulling it away from the digestive tract and reducing GI efficiency. The combination of a gas-filled stomach and reduced digestive efficiency significantly increases the risk of upper GI symptoms. For this reason, carbonated drinks are often too physically disruptive to consume immediately before or during exercise.
How Carbonation Affects Hydration Absorption
A common belief is that carbonation impedes the body’s ability to absorb water, which is a major concern for hydration. However, carbonation does not significantly alter the rate at which fluid is emptied from the stomach or absorbed in the intestines. Studies show that the gastric emptying rate for carbonated fluids is comparable to that of non-carbonated fluids. The primary way carbonation indirectly affects hydration is through the sensation of satiety it creates, causing the stomach to feel full quickly. This premature feeling of fullness results in a lower overall fluid intake, which is detrimental to proper hydration during long or hot runs.
Beyond the Bubbles: Sugar, Caffeine, and Acidity
The biggest concern for runners often lies not with the carbonation itself, but with the high-sugar, high-caffeine, and acidic nature of many carbonated drinks. Regular sodas and energy drinks contain high osmolarity due to their sugar content. When this concentrated fluid reaches the intestines, it can draw water from the body into the gut to dilute the solution, potentially causing cramping, osmotic diarrhea, and GI distress.
Caffeine, common in many carbonated beverages, functions as a stimulant but is also a known gut irritant. High doses can increase bowel motility and relax the lower esophageal sphincter, increasing the risk of reflux and urgent bathroom stops. Furthermore, nearly all carbonated drinks are acidic due to dissolved carbon dioxide and often phosphoric or citric acid. This high acidity can contribute to dental enamel erosion over time with frequent consumption.
A Runner’s Guide to Consumption Timing
The timing of carbonated beverage consumption is paramount to avoiding performance-limiting side effects. Runners should avoid all carbonated drinks in the one to two hours leading up to a run. This pre-run window ensures the digestive system is clear of anything that could cause bloating or reflux once exercise begins. During a run, carbonated beverages are not advised due to the high risk of GI distress and reduced fluid intake volume.
The jostling motion of running combined with a gas-filled stomach makes ingesting bubbles problematic. After a run, plain sparkling water is acceptable for rehydration, provided the runner is not prone to reflux. Recovery is best served by first replenishing lost fluids and electrolytes with still water or a balanced sports drink. Sugary, caffeinated sodas should be reserved for a time well outside the immediate recovery window, as their high osmolarity and caffeine content can be counterproductive to rehydration.