Why Does Sugar Trigger Diarrhea? Understanding the Digestive Impact

October 23, 2025 •

4 min read

According to the Cleveland Clinic, some sugars are harder to digest, and consuming too much can directly cause diarrhea. This happens because specific types of sugar, including fructose and sugar alcohols, are poorly absorbed, leading to a cascade of uncomfortable digestive side effects.

Quick Summary

Excess sugar, especially from poorly absorbed fructose and sugar alcohols, causes diarrhea primarily through osmotic effects, which draw water into the intestine, leading to watery stools.

Key Points

Osmotic Diarrhea: The primary mechanism involves unabsorbed sugar drawing water into the intestines, resulting in watery stools.
Fructose Malabsorption: Excess fructose overwhelms the intestine's absorption capacity, leading to fermentation by gut bacteria and symptoms like diarrhea, gas, and bloating.
Sugar Alcohols: These low-calorie sweeteners (polyols) found in 'sugar-free' products are poorly absorbed and have a laxative effect, causing gas and diarrhea.
Lactose Intolerance: A lack of the lactase enzyme prevents proper digestion of milk sugar, causing undigested lactose to ferment in the colon and trigger diarrhea.
IBS and FODMAPs: For people with IBS, fermentable sugars (FODMAPs), including many problematic sugars, can exacerbate symptoms and trigger digestive distress.
Dietary Management: Identifying individual sugar triggers through a food diary and making conscious dietary choices is the best strategy for managing symptoms.

The Primary Cause: Osmotic Diarrhea

The fundamental reason why sugar can trigger diarrhea is a process known as osmotic diarrhea. This occurs when an excess of poorly absorbed substances, such as certain sugars, remains in the intestinal lumen. These unabsorbed molecules create a higher concentration of solutes, which naturally draws water from the body into the bowel to dilute it. The result is an increased volume of fluid that overwhelms the colon's ability to absorb water, leading to loose, watery stools. This mechanism is a key contributor to digestive distress caused by a variety of sugars and sweeteners.

Fructose Malabsorption: When Fruit Isn't Sweet to Your Gut

Fructose, a simple sugar found in fruits, honey, and high-fructose corn syrup, is a common culprit. For many people, particularly those with Irritable Bowel Syndrome (IBS), the intestinal transport proteins responsible for absorbing fructose can become overwhelmed when intake is too high. This leads to unabsorbed fructose traveling to the large intestine, where it is fermented by gut bacteria. The fermentation process produces gases and short-chain fatty acids, resulting in symptoms like bloating, gas, abdominal pain, and diarrhea. The absorption of fructose is also less efficient when consumed in isolation compared to when it's accompanied by glucose.

Common Fructose Sources to Watch For:

High-fructose corn syrup (found in sodas, candies, and processed foods)
Honey and agave syrup
Certain fruits like apples, pears, and mangoes
Dried fruits and fruit juices

The Laxative Effect of Sugar Alcohols

Sugar alcohols, or polyols, are low-calorie sweeteners frequently used in sugar-free products like chewing gum, candies, and diet foods. They include sorbitol, xylitol, mannitol, and maltitol. Like fructose, these compounds are not completely absorbed by the small intestine and instead make their way to the large intestine where they are fermented by bacteria. This causes gas, bloating, and an osmotic effect that pulls water into the colon, causing diarrhea. The severity of the laxative effect depends on the specific sugar alcohol and the quantity consumed.

Foods High in Sugar Alcohols:

Sugar-free gum and candies
Diet sodas and some processed foods
Certain baked goods and ice cream
Cough drops and syrups

Lactose Intolerance: The Dairy Sugar Dilemma

Lactose is a disaccharide sugar found in milk and other dairy products. For digestion, it requires the enzyme lactase, which is produced in the small intestine. A lack of sufficient lactase, a condition known as lactose intolerance, means the body cannot break down and absorb lactose properly. The undigested lactose then proceeds to the colon, where it is fermented by bacteria, causing gas, bloating, cramps, and osmotic diarrhea. Lactose intolerance is particularly common among people of Asian, African, and Native American descent.

Sugar and Irritable Bowel Syndrome (IBS)

For individuals with sensitive digestive systems or IBS, sugar can be a major trigger. Many problematic sugars, including fructose, lactose, and sugar alcohols, fall under a category known as FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). These poorly digested carbohydrates ferment in the gut, exacerbating typical IBS symptoms like abdominal pain, bloating, and diarrhea. A low-FODMAP diet, which involves reducing the intake of these fermentable sugars, has been shown to be an effective strategy for managing symptoms in many IBS patients.

Comparison of Sugars and Their Digestive Impact


Sugar Type	Primary Mechanism	Symptoms	Common Sources
Fructose	Malabsorption and fermentation by gut bacteria, causing an osmotic effect.	Diarrhea, bloating, gas, abdominal pain.	High-fructose corn syrup, fruits, honey, agave.
Sugar Alcohols	Incomplete absorption and fermentation by gut bacteria, leading to an osmotic effect.	Diarrhea, bloating, gas.	Sugar-free gum, candy, diet foods, cough drops.
Lactose	Insufficient lactase enzyme, preventing proper digestion.	Diarrhea, gas, bloating, abdominal cramps.	Milk, cheese, yogurt, ice cream.
Sucrose	Reduced enzymes in the small intestine (Sucrase-Isomaltase Deficiency) cause malabsorption and fermentation.	Watery diarrhea, gas, bloating, abdominal pain.	Table sugar, many processed sweets.

How to Manage and Identify Sugar-Related Diarrhea

Managing sugar-induced diarrhea involves careful dietary adjustments. The first step is to identify your specific triggers. Keeping a food diary can help you connect your symptoms to certain sugars or sweeteners. For those with diagnosed intolerances, like lactose or fructose malabsorption, following specific dietary guidelines is crucial. For example, individuals with lactose intolerance can choose lactose-free products or take a lactase enzyme supplement. Those sensitive to sugar alcohols should read labels and moderate their intake of sugar-free products. As mentioned by the NIH, the absorption of fructose is improved when it is combined with glucose, which may explain why certain fruits are better tolerated than others.

For those with IBS, a low-FODMAP diet is often recommended to reduce symptoms. It's important to remember that dietary changes should be made gradually, as sudden, restrictive changes can be hard to maintain and may not be necessary for everyone. Consulting a healthcare professional or a registered dietitian is always the best approach to developing a personalized plan for managing sugar-related digestive issues. If symptoms persist or are severe, seeking medical advice is essential to rule out other underlying conditions.

Conclusion

Diarrhea triggered by sugar is not a single issue but rather a symptom with several underlying causes, primarily rooted in the poor absorption of certain carbohydrates. Mechanisms such as osmotic diarrhea, fructose malabsorption, and the laxative effects of sugar alcohols are the main culprits. Conditions like lactose intolerance and Irritable Bowel Syndrome significantly heighten sensitivity to these effects. By understanding the specific types of sugar your body struggles with and making informed dietary adjustments, you can effectively manage symptoms and improve your digestive health. Remember that moderation, careful label reading, and seeking professional guidance are key steps toward finding relief.

Frequently Asked Questions

Osmotic diarrhea occurs when poorly absorbed substances, like certain sugars, stay in the intestine and draw water into the bowel to balance the concentration. This excess fluid leads to watery stools. When the body can't absorb a sugar properly, that sugar creates this osmotic effect.

Fructose is a simple sugar, and some people have a reduced capacity to absorb it, a condition called fructose malabsorption. When unabsorbed, it travels to the large intestine where bacteria ferment it, producing gas and causing an osmotic effect that results in diarrhea.

Yes, many artificial sweeteners are sugar alcohols (polyols), such as sorbitol, xylitol, and mannitol, which are known to have a laxative effect. They are poorly absorbed by the body, leading to fermentation and drawing water into the intestines, causing bloating, gas, and diarrhea.

A sugar intolerance is a digestive issue where the body has difficulty digesting a specific sugar, often due to an enzyme deficiency, like with lactose or sucrose intolerance. A sugar allergy, which is much rarer, involves an immune system response to sugar proteins and can cause more severe, potentially life-threatening reactions like hives or anaphylaxis.

FODMAPs are a group of fermentable carbohydrates that are poorly absorbed and can cause digestive issues. This group includes fermentable sugars like fructose and polyols (sugar alcohols), which can cause diarrhea in sensitive individuals, especially those with IBS.

The first step is to keep a food diary to track your food intake and corresponding symptoms. For specific intolerances like fructose or lactose, doctors can perform hydrogen breath tests to confirm malabsorption. A healthcare provider can then help you with an elimination diet to pinpoint triggers.

Not necessarily. The key is identifying and moderating the specific types of sugar that trigger your symptoms. For many, only certain sugars or quantities cause a problem. Consulting a doctor or dietitian can help create a balanced diet plan that avoids triggers while maintaining good nutrition.