Why Do You Have Diarrhea After Fasting? Causes & Treatment

Key takeaways:

• Fasting causes changes in your gastrointestinal tract related to gut motility and digestion.
• It is normal to experience a few days of mild diarrhea after fasting.
• The food you choose to eat when breaking your fast can impact whether you experience diarrhea.

Experiencing diarrhea after fasting can be confusing, especially when you are coming off of a period of consuming no food. Whether you've completed an intermittent fast or a longer period of no food, your body may react in unexpected ways once food is reintroduced.

This article will explain the common causes of diarrhea after fasting, how to manage it, and when to consult a healthcare professional.

Is it normal to have diarrhea after breaking a fast?

When you alter your diet, whether it is the food you are eating, the timing of your meals, or periods of fasting, you are altering how your digestive tract behaves.

By going from a period of not eating to the reintroduction of food, the bowels have to adapt and adjust. It is normal to experience short-term diarrhea during this adaptive period.

Typical duration of diarrhea after fasting

For most people, diarrhea that occurs after fasting is temporary and resolves within a few days. It is usually associated with the body readjusting to the reintroduction of food.

The duration can vary depending on the individual and the type of fast. Diarrhea after shorter fasts usually resolves more quickly than diarrhea after longer fasts.

Causes of diarrhea after fasting

Fasting has been a popular dietary method in recent years, and it promises to help people lose weight and improve their chronic medical conditions. The side effects one might experience with or after completing a fast aren’t discussed as frequently.

There are a few different reasons why someone may experience a symptom such as diarrhea after fasting, which are outlined below.

Exacerbation of underlying conditions

There are several medical conditions, such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD), that can cause diarrhea.

These conditions are typically managed with a balance of medications and a fine-tuned diet. Studies have found that fasting periods can alter the gut’s state, sometimes leading to exacerbations of these conditions and causing worsening symptoms such as diarrhea.

Refeeding syndrome

Refeeding syndrome refers to medical complications that occur when someone is given nutrition after periods of starvation or fasting. It can occur after as little as 48 hours of fasting.

Refeeding syndrome can lead to metabolic and electrolyte disturbances that impact multiple body systems. Gastrointestinal symptoms associated with refeeding syndrome include diarrhea, nausea, and vomiting. Refeeding syndrome is a medical emergency that requires immediate intervention.

Increased gut motility

Fasting can increase motility or the speed at which food moves through the intestines.

When you break your fast, the increased motility may result in diarrhea, especially if you eat foods that are difficult to digest, such as dairy, spicy foods, or foods high in dietary fiber.

Changes in gut bacteria

Fasting has been linked to changes in the gut microbiota, which are the healthy microorganisms living in the gut.

More specifically, these changes have been linked to inflammation that can trigger inflammatory bowel diseases and may also make the bowel more prone to opportunistic bacterial infections that can cause diarrhea.

How to get relief from or stop diarrhea after fasting

Diarrhea after fasting is usually temporary and will resolve within a few days. However, there are a few things to try to help speed up the resolution of this symptom.

Gradual reintroduction of food

Start with small portions of easily digestible foods rather than immediately eating large meals after a fast.

This approach gives your digestive system a chance to ease back into the process of digesting food, minimizing the risk of overwhelming the gut and triggering diarrhea.

Dietary choices

When eating after fasting, you should focus on eating foods that are easy to digest and avoiding foods that are known triggers of diarrhea. Consuming a bland diet allows the gastrointestinal tract to rest because it consists only of foods that are easy to break down.

Some examples of good food choices include eggs, broth, lean meats like chicken and fish, and low-fiber vegetables. Fried food, spicy food, and high-fiber vegetables should be avoided as first-choice foods after fasting.

Probiotics

Probiotics can be used for both the prevention and treatment of diarrhea. Probiotics can help regulate an imbalance of intestinal bacteria that may contribute to diarrhea.

Knowing that fasting can disrupt the normal gut microbiota, probiotics can be useful in regulating the growth of beneficial microorganisms. Research shows that Saccharomyces boulardii and Lactobacillus reuteri are the two most effective types of probiotics for reducing diarrhea.

Read our guides on different types of diarrhea and common causes of diarrhea for more.

When you should see a doctor for diarrhea after fasting

Experiencing diarrhea after fasting can be normal if it resolves on its own within a few days. Here are a few signs and symptoms to look out for that would indicate the need to see a healthcare provider:

You should see a doctor if:

• Diarrhea lasts more than a few days after fasting.
• You experience associated abdominal discomfort or bloating.
• You have signs of mild dehydration (dry mouth, increased thirst, dark urine).

You should go to the emergency room if:

• You are unable to tolerate fluids for more than 24 hours.
• You notice significant amounts of blood in the stool or white, gray, or black discoloration of the stool.
• You have signs of severe dehydration, such as dizziness, headache, and heart palpitations.

Questions to ask your doctor about diarrhea after fasting

• Is it normal to experience diarrhea after fasting?
• How long should I expect my symptoms to last?
• What can I do in the future to prevent diarrhea after a fast?
• Can I take supplements to support my gut health during a fast?

How a doctor can help treat diarrhea after fasting

If you are experiencing diarrhea after fasting that is not resolved with home remedies, your healthcare provider may have some additional ways to help with your symptoms.

Nutritional and dietary guidance

Diet plays an important role in healthy and normal bowel movements. With so many dietary recommendations, from intermittent fasting to the BRAT diet, to a bland or low-residue diet, knowing what to eat and when can be confusing.

If you struggle to optimize your diet to control diarrhea after fasting, your doctor may give you a diet plan to follow or recommend you meet with a dietician to develop a specialized diet plan.

Hydration

Severe cases of diarrhea can lead to significant volume and fluid loss and dehydration. Hydration is the single most important step when it comes to managing diarrhea.

If you are experiencing diarrhea, you should focus on increasing your fluid intake of water and electrolyte-containing drinks. Taking small, frequent sips of fluids will lead to better tolerability of the increase in fluid intake. Drinking chicken and vegetable broth can help with hydration while providing some nutritional benefits.

Medication

If your symptoms are persistent despite conservative changes in diet, medication may be necessary.

Your healthcare provider may recommend an over-the-counter medication such as Imodium or Pepto-Bismol. They may also recommend you take a probiotic. In extreme cases, they may recommend a prescription for anti-diarrhea medication.

Read our full guide on treating diarrhea for more.

Frequently asked questions: diarrhea after fasting

If you are experiencing diarrhea after fasting, you may have questions about whether this symptom is normal and what to expect. Below are some of the most commonly asked questions about diarrhea after fasting.

What if you find mucus in your diarrhea or stool after fasting?

Finding mucus in your stool after fasting may indicate that your intestines are irritated or inflamed. Inflammation can occur as a result of alterations in the gut microbiota. It can also be due to increased bowel work when digesting those first few meals after a fasting period.

Inflammation usually resolves within a few days as your gut adapts to digesting food. Still, if you notice ongoing mucus in your stool beyond more than a few days, you should discuss this with your healthcare provider.

Does intermittent fasting cause diarrhea?

Studies have found that continuous periods of fasting can lead to starvation symptoms such as chronic diarrhea, anemia, and excessive weight loss.

While this is not common with intermittent fasting, some people may experience diarrhea if it is practiced too frequently or for too many continuous days. Diarrhea may also occur when starting intermittent fasting as your body adapts to this way of eating.

Is it normal to get diarrhea after a 24 hour fasting period?

No set period of fasting time that is linked to diarrhea. The bottom line is that any big or small changes in dietary habits can lead to adaptive and reactive symptoms in the gastrointestinal tract, such as diarrhea.

Managing diarrhea after fasting

Experiencing diarrhea after fasting is usually a temporary symptom resulting from changes in gut motility, gut microbiota, and reintroduction of food after a period of restriction. Focusing on slowly reintroducing bland and easy-to-digest foods can help prevent or minimize symptom severity. If diarrhea persists beyond a few days or is accompanied by other symptoms, this should prompt a visit with your healthcare provider.

General Medicine follows a strict editorial process, including using real experts to write our articles, vetted primary sources, fact-checking, a secondary medical review, and updates as necessary. This article was medically reviewed and fact checked by Dr. Pallabi Sanyal-Dey, MD.

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Persaud-Sharma, Dharam, et al. “Refeeding Syndrome.” StatPearls, StatPearls Publishing, 7 November 2022. https://pubmed.ncbi.nlm.nih.gov/33232094/

Tibi, Sedra et al. “Implications of Ramadan Fasting in the Setting of Gastrointestinal Disorders.” Cureus vol. 15,3 e36972. 31 Mar. 2023, doi:10.7759/cureus.36972 https://pmc.ncbi.nlm.nih.gov/articles/PMC10151003/

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