What Causes Diarrhea after Fasting and How to Avoid It

author avatar Dr. Eric Berg 05/18/2024

Prolonged fasting has gained popularity due to its impressive health benefits. Caloric restriction has been linked to improved brain function, enhanced immune defenses, and significant weight loss.

However, a prolonged fast can lead to digestive issues, including diarrhea, if you break your fast with the wrong foods.  

Learn about the causes of diarrhea after fasting and how to prepare for a prolonged fast to maximize health benefits.

Fasting alarm clock on plate

What causes diarrhea after fasting?

Prolonged fasting, which can last from 24 hours to several days, can trigger significant physical and psychological effects.

Diarrhea, loose stools, gas, abdominal pain, bloating, or nausea are common side effects that can occur after fasting. 

The risk of gastrointestinal (GI) issues during or after prolonged fasting periods depends on several factors. These include how the fast is broken, the individual's health status, and what has been consumed before, during, and after the fast.

One of the primary benefits of prolonged fasting is that it enables the body to redirect energy from digestive processes to other physiological functions. This helps improve metabolic pathways, enhances cognitive function, and triggers autophagy, a process of cell repair and renewal.

When the digestive system slows and rests during fasting, the production of essential digestive components such as hydrochloric acid, enzymes, and bile temporarily decreases.  

A sudden reintroduction of hard-to-digest foods after a prolonged fast can overwhelm the GI system. This can cause accelerated movement of contents through the digestive tract, leading to incomplete digestion, reduced nutrient absorption, and diarrhea.

Watch this video to learn more about potential digestive issues after breaking a fast.

Digestive Issues When Breaking a Fast?

What is refeeding syndrome? 

Refeeding syndrome is a severe metabolic condition linked to excessive intake of carbohydrates after a period of prolonged fasting or malnutrition, leading to severe electrolyte and fluid imbalances. 

This typically happens if essential nutrients, particularly electrolytes, are not maintained before and during the fast.

As Dr. Berg explains, "Fasting drastically lowers insulin levels. Suddenly eating carbs and sugar can cause a sharp spike in insulin, leading to a profound shift in fluid and electrolyte distribution, which can create significant health issues."

One primary concern is the significant reduction in blood volume caused by the sudden movement of fluid into cells. This can diminish blood flow to vital organs, impairing their function and placing them under considerable stress.

Furthermore, the influx of fluids into cells may lead to cellular swelling, also known as edema. This swelling can disrupt normal cellular function and, in severe cases, may cause cell damage or even cell death.

Symptoms of refeeding syndrome may include:

  • Fainting

  • Lightheadedness

  • Weakness

  • Extreme mood swings

  • Severe cramping

  • Respiratory distress

  • Heart palpitations

To help prevent refeeding syndrome, it's essential to avoid breaking a fast with foods high in carbs or sugars and maintain optimal electrolyte balance before and throughout the fast.

Healthy body holding the word detox

Benefits of prolonged fasting 

Despite the potential for digestive issues, prolonged fasting offers various potential health benefits that can positively impact physical and mental well-being. 

Some of the benefits linked to prolonged fasting include:

  • Improved brain function

  • Enhanced energy levels 

  • Cellular repair and regeneration 

  • Anti-aging effects

  • Increased production of stem cells

  • Anti-inflammatory effects 

  • Decreased tumor growth

  • Improved cellular resistance to stress

  • Weight loss

  • Enhanced gut health

  • Better blood glucose control 

Preparing an electrolyte powder drink

How to prepare for a prolonged fast 

Properly preparing for prolonged fasting helps prevent complications, including diarrhea and refeeding syndrome. This also ensures you get the maximum possible benefits from your fast.

Here are five ways to prepare yourself for a successful prolonged fast.

1. Stay hydrated and maintain electrolyte balance

Ensure you are well-hydrated before and during your fast by drinking plenty of water and supplementing electrolytes such as sodium, potassium, and magnesium. 

Taking a zero-calorie, sugar-free electrolyte powder or capsule is an excellent strategy to maintain the body’s electrolyte balance. Electrolyte supplementation also supports energy production and fluid balance while preventing the risk of nutritional deficiencies during caloric restriction.

In addition, you can enjoy calorie-free beverages during your fast, such as herbal teas, sparkling water, and mineral water, to promote the body’s fluid balance and stay hydrated. 

However, be cautious with zero-calorie sweeteners, which can irritate the GI tract and trigger cravings.

Healthy food meal plan preparation

2. Prepare your refeeding meal plan

Refeeding with the wrong foods is one of the biggest prolonged fasting mistakes

It’s critical to have a healthy refeeding plan in place before starting a fast to prevent accidental binges on foods high in sugar and carbohydrates that can lead to potentially dangerous side effects, including refeeding syndrome.

Moreover, a study published in Nutrients found that refeeding with carbohydrates temporarily induced insulin resistance, potentially increasing the risk of metabolic imbalances.

It's recommended to create a post-fast meal plan that starts with easy-to-digest foods such as bone broth and soup and gradually introduces more complex foods such as steamed vegetables and protein.


3. Limit caffeine 

If you consume large amounts of caffeine or other stimulants, consider reducing your intake before fasting. This can help prevent withdrawal symptoms such as headaches and irritability and help maintain hydration and mineral balance.

In addition, while zero-calorie drinks are technically allowed while fasting, caffeinated beverages such as coffee and green tea may not be the best choice due to their high tannin content.

Tannins are a type of polyphenol that can irritate the stomach lining, leading to intestinal discomfort and nausea, especially when consumed on an empty stomach.

Eating healthy probiotic Greek yogurt

4. Eat nutritious pre-fast meals

Before fasting, consume nutritionally balanced meals rich in healthy fats and dietary fiber to help sustain satiety and maintain nutrient stores while feeding beneficial gut bacteria.

However, you may benefit from reducing your protein intake prior to fasting. According to research published in The Israel Medical Association Journal, “A protein-poor pre-fast meal is likely to be followed by easier fasting.”

5. Consult a healthcare professional

Before beginning a fasting regimen, discuss caloric restriction with a healthcare professional to ensure that fasting won't adversely affect your health. This is especially important if you have pre-existing health conditions or are at increased risk of nutrient deficiencies.

Persistent and chronic diarrhea can lead to severe dehydration, which is linked to various serious health issues. It’s crucial to consult a doctor immediately if you develop sudden and significant gastrointestinal symptoms after breaking a fast.

A healthcare provider may consider fluid and electrolyte replacement and prescribe anti-diarrheal medications to treat diarrhea.

Women preparing to eat avocado

How to break a prolonged fast

It's essential to listen to your body when fasting. If you feel weak or lightheaded, it's better to eat than continue fasting. 

To reduce the risk of watery bowel movements and potential refeeding syndrome, it’s important to gradually break a fast with easily digestible foods.


Start with small low-carb meals, such as cooked vegetables and bone broth, and gradually introduce easily digestible proteins like fish, chicken, or egg.

In addition, taking digestive enzymes and probiotic supplements or eating probiotic foods such as kefir may also be beneficial, especially if you are prone to diarrhea or loose stools.

It’s also recommended to avoid consuming nuts, nut butter, red meat, raw cruciferous vegetables, protein powders, sugar, and zero-calorie sweeteners, as they require more digestive effort and may overwhelm the digestive tract. 

A healthy meal after fasting

Key takeaways

Diarrhea after fasting is often caused by electrolyte imbalances or linked to the consumption of hard-to-digest foods that can overwhelm the digestive system. 


To minimize the risk of diarrhea and potentially life-threatening conditions such as refeeding syndrome, break your fast gradually with easily digestible, nutrient-dense foods, stay hydrated, and maintain electrolyte balance throughout your fast.  


1. Is it normal to have diarrhea after fasting?

Yes, it can be normal to experience diarrhea after breaking your fast, as the gastrointestinal tract may need time to reactivate after prolonged fasting periods.  

Breaking a fast with hard-to-digest meals or foods high in carbs and sugars can overwhelm the gastrointestinal tract, leading to incomplete digestion and loose bowel movements. 

2. What are the digestive side effects of prolonged fasting?

Dizziness, headaches, mood swings, lethargy, and diarrhea during fasting are all potential side effects.

These symptoms can occur as the digestive system adjusts to caloric restriction but may also be linked to electrolyte deficiency or lack of adequate fluid intake during fasting periods.  

3. What are the benefits of prolonged fasting? 

Prolonged fasting has various health benefits, including improved brain function, increased cellular regeneration, reduced inflammation, and may potentially decrease the risk of type 2 diabetes and cardiovascular disease.

4. What is the best way to break a prolonged fast?

The best way to break a prolonged fast is to reintroduce food gradually. Start with small, light meals that are easy to digest, such as broth, cooked vegetables, or a small portion of probiotic yogurt. 

Avoid foods that are difficult to digest, as they are more likely to trigger diarrhea and other gastrointestinal symptoms. 

5. Can diarrhea happen after intermittent fasting?

Diarrhea is less likely to occur with intermittent fasting. However, breaking an intermittent fast with hard-to-digest foods can increase the risk of gastrointestinal issues, including loose stools. 


  1. https://www.mdpi.com/2072-6643/14/6/1183 

  2. https://pubmed.ncbi.nlm.nih.gov/11574981/

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