Osmotic diarrhea is when undigested material reduces how much water and electrolytes the bowels can absorb. It can occur when a person’s body has difficulty digesting certain foods, such as lactose.

Dietary changes can help ease osmotic diarrhea.

This article examines osmotic diarrhea and compares it with other kinds of diarrhea. It also explains its symptoms, causes, treatment, and outlook.

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Healthcare professionals define diarrhea as more than three bowel movements that are loose or watery within 24 hours. There are several different types of diarrhea.

Osmotic diarrhea is diarrhea that arises from the presence of undigested material in a person’s bowels. This prevents the bowels from absorbing typical amounts of water and electrolytes.

The result is a greater amount of watery stool.

According to a 2022 review, diarrhea can have the following symptoms:

  • large volumes of stool
  • passing stool very frequently
  • mushy or watery stool
  • discolored stool

With osmotic diarrhea, a person may see undigested food in the stool. These are the foods that have caused difficulties absorbing fluids and electrolytes.

There are several possible causes of osmotic diarrhea.

Carbohydrate malabsorption

When the body does not absorb certain carbohydrates efficiently, these foods may draw water into the intestines. This can lead to osmotic diarrhea.

This can happen if a person has an intolerance to carbohydrates such as lactose, maltose, sucrose, or fructose. It can also occur due to digestive disorders such as celiac disease.

Certain medications

Several medications can cause osmotic diarrhea. In the case of laxatives, this is the intended effect. However, some medications may cause osmotic diarrhea as an adverse effect.

According to a 2019 case report, the sweeteners sorbitol and xylitol can cause osmotic diarrhea. Sorbitol and xylitol are common ingredients in chewing gum.

The case report describes how an individual developed osmotic diarrhea after chewing lots of sorbitol-containing gum.

Avoiding triggers of osmotic diarrhea can help with this condition. For instance, people with lactose intolerance should avoid lactose or only consume lactose-containing products with lactase supplements.

Sometimes, the only treatment option is to address the underlying condition, such as celiac disease.

If the cause is related to medication, a doctor will need to assess a person’s medication and decide whether the person should continue taking it. Never change dosage or stop taking a medication without a doctor’s approval.

Diarrhea is not often something to worry about. However, the National Institutes of Health advises seeking immediate medical attention under certain circumstances.

For adults, these are:

In children, the following symptoms require immediate medical attention:

Older adults and people with weakened immune systems or other health conditions who have diarrhea should also contact a doctor immediately.

There is not much research on the outlook for people with osmotic diarrhea.

Unlike secretory diarrhea, osmotic diarrhea does not arise from infections. Osmotic diarrhea can also sometimes occur alongside secretory diarrhea. Secretory diarrhea is a type of diarrhea that occurs when the body secretes fluids and electrolytes into the intestines.

Acute osmotic diarrhea can resolve with fasting. A person may also be able to prevent it by avoiding certain dietary triggers.

Acute osmotic diarrhea is not often serious, but chronic osmotic diarrhea may be serious. A person should contact a doctor if they experience diarrhea that does not resolve over time.

This section answers some frequently asked questions about osmotic diarrhea.

What is the difference between secretory and osmotic diarrhea?

Osmotic diarrhea is when undigested materials make it more difficult for the bowels to absorb fluids and electrolytes.

Secretory diarrhea is when the body, often in response to infection, secretes too many fluids and electrolytes into the bowels.

How does osmotic diarrhea appear?

People with osmotic diarrhea may pass larger volumes of watery or mushy stool. This stool could contain traces of undigested carbohydrates.

Osmotic diarrhea is when the bowels do not absorb enough fluid or electrolytes. This occurs when there are undigested materials in the bowels.

The result is a watery stool, which may contain evidence of undigested materials.

This form of diarrhea can have several causes. For instance, people with celiac disease and lactose intolerance can develop osmotic diarrhea. Certain medications and sweeteners, such as sorbitol, can also have this effect.

Fasting can resolve acute osmotic diarrhea. In the case of chronic osmotic diarrhea, a person should contact a doctor and dietician to obtain a workup for the underlying cause.