Diarrhea during fasting is uncommon because a person will not consume any food during this time. However, if an individual does experience diarrhea, they may need to stop their fast or speak with a doctor to determine causes and treatments.

Fasting is a process where people restrict eating and sometimes drinking over a period of time.

People may fast for health reasons, such as managing weight, blood sugar, or blood pressure. The time when people choose to fast this may vary. For example, some people may fast for a full day or follow a dietary regime, such as the 16:8 intermittent fasting method.

Also, people of different faiths may practice fasting due to religious reasons, including in Christianity, Islam, Buddhism, Judaism, amongst others.

While a person may experience certain effects from fasting, diarrhea is not a common one. Yet other factors, such as Crohn’s disease, could contribute to diarrhea during fasting.

This article looks at whether fasting causes diarrhea, the effects of diarrhea during fasting, and whether breaking the fast causes diarrhea. It also explores when to consult a doctor and how to treat diarrhea during fasting.

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Medical News Today sought the expertise of Kelsey Costa, a registered dietitian and nutrition consultant for the National Coalition on Healthcare, who explains that fasting may not directly cause diarrhea.

“When the body is in a fasting state, our gut motility — or how food moves through the digestive tract — changes,” Costa said.

“Normally, consuming food stimulates the ‘gastrocolic reflex’ and triggers bowel movements. When we fast, this reflex slows down due to lack of food stimulation,” she added.

Still, changes in gut motility and dietary habits associated with fasting can lead to diarrhea.

Learn more about what causes diarrhea.

Experiencing diarrhea, especially during fasting, may become dangerous if it leads to severe dehydration or malabsorption. These conditions can cause additional symptoms and may require emergency medical attention.

Symptoms of dehydration may include:

Symptoms of malabsorption in adults may include:

Breaking the fast can sometimes lead to diarrhea.

According to Costa, “Once we break the fast and start eating again, the sudden influx of food can overstimulate the gastrocolic reflex, leading to accelerated bowel movements and potentially diarrhea.”

Consuming certain foods to break the fast can worsen this reaction.

“High fat or high sugar foods can cause ‘dumping syndrome,’ where food is pushed into the small intestine before it’s properly broken down, often resulting in diarrhea,” said Costa.

Before starting a fast or if a person has any health conditions that fasting may affect, it is important to discuss their options with a doctor.

If a person has started the fast and is experiencing diarrhea, along with any of the following symptoms, they should consult their doctor immediately:

Certain treatments are available for diarrhea during fasting, including:

Over-the-counter (OTC) medications

In most cases, people may be able to treat diarrhea with OTC medications such as loperamide (Imodium) and bismuth subsalicylate (Pepto-Bismol, Kaopectate).

However, doctors do not recommend OTC treatments for people with additional symptoms, such as bloody stools or fever. If the diarrhea persists, people should consult their doctor for alternative treatments.

Prescription medications

Treatment for persistent and chronic diarrhea depends on the cause. Doctors may prescribe antibiotics to treat certain bacterial or even parasitic infections.

Doctors may also prescribe medications to treat some conditions that cause chronic diarrhea, such as Crohn’s disease, ulcerative colitis, or irritable bowel syndrome (IBS).


Probiotics may be useful in some cases. Researchers are still studying probiotics and their role in treating diarrhea, so a person must speak with a doctor before using them. Generally, though, they are safe to use.

Drinking fluids

Staying well hydrated when experiencing diarrhea, for any reason, is important. If a person’s fast does not include water, they should strongly consider breaking the fast to drink water and replace lost fluid and electrolytes when experiencing diarrhea.

Read more about possible remedies for diarrhea.

Ending fast

Sometimes, a person may want to break their fast due to diarrhea.

In some religions, such as Islam, physical effects of fasting like diarrhea are an acceptable reason to break the fast in order to avoid possible complications.

Diarrhea does not usually occur with fasting since a person consumes no food that the body needs to digest.

People tend to experience diarrhea when breaking a fast, as bowel functions resume when consuming food and drink. A person should speak with a doctor if they have any concerns or severe symptoms before, during, or after a fast.

Various OTC or prescription medications exist for treating diarrhea from fasting. Sometimes, a person may want to end the fast. Emergency care is vital for cases of severe dehydration and malabsorption.