Seltzer water, made by infusing still water with carbon dioxide gas, has become a popular substitute for sugary sodas and juices. This carbonated water, often flavored and zero-calorie, is generally regarded as a healthy hydration option. For some individuals, however, seltzer can trigger digestive upset, including loose stools or diarrhea. While plain seltzer is typically benign, the addition of carbonation and certain sweeteners found in many flavored varieties can lead to gastrointestinal distress.
How Carbonation Affects Digestion
The signature fizz of seltzer water comes from dissolved carbon dioxide (\(\text{CO}_2\)) gas. When this gas enters the digestive system, it introduces gas directly into the stomach, causing the stomach wall to distend.
This gastric distension is often perceived as fullness, bloating, or discomfort, frequently resulting in belching. For sensitive people, especially those with Irritable Bowel Syndrome (IBS), this gas accumulation can irritate the intestinal tract. The resulting abdominal distension stimulates increased gastrointestinal motility, the muscular movement that propels contents through the digestive tract.
Increased motility means waste moves more quickly through the intestines, leaving less time for water to be absorbed. This faster transit time can result in stools that are softer or looser than normal. These physical effects are a direct mechanical factor contributing to digestive discomfort.
The Impact of Artificial Sweeteners
The most significant factor linking seltzer water to diarrhea lies in the non-caloric additives used to flavor many commercial brands. While plain seltzer is generally safe, flavored products often contain sugar alcohols or high-intensity artificial sweeteners known to have a laxative effect. These ingredients are poorly absorbed by the small intestine and are the primary chemical cause of seltzer-induced loose stools.
Sugar alcohols, also known as polyols, include compounds like sorbitol, xylitol, erythritol, and maltitol. Because these molecules are not fully taken up into the bloodstream, they remain in the intestinal lumen, creating an osmotic effect. This mechanism involves the unabsorbed polyols drawing excess water from the body’s tissues into the large intestine.
The resulting increase in water volume within the colon leads directly to osmotic diarrhea. Consuming a sufficient quantity of these sweeteners can result in watery stools. Sucralose, a common high-intensity sweetener, can also cause digestive distress in sensitive individuals by being poorly absorbed.
When to Stop Drinking Seltzer Water
While temporary bloating or mild loose stools are generally harmless, persistent or severe symptoms warrant a change in consumption habits. Stop drinking seltzer immediately if you experience signs of dehydration, such as excessive thirst, fatigue, dizziness, or reduced urination. Any instance of blood in the stool or severe, unrelenting abdominal cramping should prompt an immediate consultation with a healthcare professional.
A practical step for identifying the source of discomfort is to switch from flavored seltzer to plain, unflavored carbonated water, or still water. If symptoms subside when drinking the unflavored version, the problem is likely tied to the artificial sweeteners or flavor additives. If symptoms continue even with plain seltzer, the carbonation itself may be aggravating a pre-existing condition, such as IBS or chronic acid reflux, and it may be best to stick to still water entirely.