Why Does Intermittent Fasting Cause Diarrhea?

Why Does Intermittent Fasting Cause Diarrhea?
Cordelia Tan

Cordelia Tan | Author

Cordelia Tan, is a passionate advocate for women's health and well-being. Known as Fasty's number one fan, she expertly blends Eastern and Western health practices, offering a holistic approach to diet and wellness. Her work focuses on empowering women with knowledge and practical strategies for a healthier life.

Although rare, you may experience diarrhea during intermittent fasting. This typically happens when food and liquids pass through the gastrointestinal tract too quickly without getting absorbed properly. Intermittent fasting doesn’t cause diarrhea, so other factors may be the underlying reason. If you experience diarrhea symptoms during a fast, end your fast immediately and avoid it until you’re feeling better.

Diarrhea During Fasting

You may wonder why you’re experiencing diarrhea if you’re not eating while fasting. Understand that the food you’ve consumed before starting your fast takes time to move through the digestive system. So you may experience diarrhea because of that food or some other reason. 

Diarrhea isn’t a common side effect of intermittent fasting. So, it’s very much possible that another underlying cause exists. This could be something you’ve eaten or drank. For instance, too much caffeine can cause diarrhea

Other possible causes include:

  • Medical conditions such as Crhon’s disease

  • Food intolerance (for example, dairy)

  • Viruses

  • Overhydration 

If you’re consuming way too much water while fasting, your kidneys may not be able to remove enough water, which, in turn, causes diarrhea. 

It’s important to know exactly when diarrhea begins during your fast. If you experience it at the beginning of the fast, what you’ve consumed before the fast likely has something to do with it. If you experience it a bit later into your fast, you may have a virus or are overhydrated. With the Fastic app, you can track the exact duration of your fast, which will help you time everything happening during the fast, including any side effects. 

Diarrhea After Fasting

You’re more likely to experience diarrhea after your fast than during. That’s when you’ll consume food, and if there’s something wrong with your digestive system, the food won’t get digested as it should. 

Again, fasting may not necessarily be the cause behind diarrhea during your feeding window. You may experience diarrhea because of the food itself or another underlying condition. 

When you’re fasting, the gastrocolic reflex, which triggers bowel movement has slowed down. But once you break the fast, it’s stimulated again. What you eat to break your fast matters a lot, as some foods can overstimulate the gastrocolic reflex and cause diarrhea. These are typically high sugar and high fat foods. 

In other words, the food moves through to the small intestine too quickly and is expelled before it can be digested and absorbed properly. 

It’s important to be mindful of what you break your fast with. Ideally, you should begin by eating things that don’t trigger a sudden spike in insulin production, that is, don’t break the fast with sugary or fatty foods. 

why does intermittent fasting cause diarrhea

Other Side Effects Associated with Diarrhea

If you’re experiencing diarrhea when practicing intermittent fasting, you may also experience one or more of the following symptoms:

  • Lightheadedness and dizziness

  • Thirst 

  • Dry mouth

  • Fatigue

  • Low urine output 

  • Dark urine

Diarrhea is often linked with dehydration which can result in symptoms such as dark-colored urine or very little urine. 

Interestingly enough, if you have diarrhea because of overhydration, you won’t have the urine-related symptoms.

What to Do If You Have Diarrhea While Intermittent Fasting?

If you have diarrhea while fasting, break your fast and consume foods that don’t make your condition worse. 

Of course, it’s essential to stay hydrated, so you should drink plenty of water and other fluids like broths or low-sugar juices. Avoid sugary or caffeinated drinks, as those will actually lead to dehydration and worsen your diarrhea. 

Eat foods that are high in soluble fiber. These include cereals, grains, vegetables, and fruits. Soluble fiber will help absorb excess water in your digestive tract and allow the food to be digested slowly. But don’t eat too much either. 

Gradually work your way to introducing other foods as your diarrhea symptoms improve. 

Over the counter medications like imodium can also help with diarrhea. 

If you continue to experience diarrhea even after taking the above steps, you should see a doctor. Also, see a doctor if you experience pain in bowel movement or see blood in the stool. These are serious symptoms that require medical attention. 

Avoid intermittent fasting until you’re in the clear and diarrhea symptoms have gone away. 

Preventing Diarrhea During Intermittent Fasting

As mentioned, fasting won’t really cause diarrhea. But how you break your fast and what you consume during or after your fast may be a probable cause. Poor food choices or allergies are often the underlying causes. 

It’s best to stick with healthy foods that help with digestion. Don’t drink too much of caffeinated drinks during your fast or the feeding period. 

Use the Fastic app to keep a track of what you consume, so you can make healthy choices throughout your intermittent fasting journey. 

Disclaimer: It is advised to speak with a health professional before beginning intermittent fasting or a diet program. There may be side effects for people with certain medical conditions.

With Fastic, millions of people have achieved their desired weight, overcome disease and regained their quality of life.

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