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Home arrow Nutrition arrow Intermittent Fasting arrow Intermittent Fasting and Diarrhea: Is It Normal?

Intermittent Fasting and Diarrhea: Is It Normal?

Written by Edibel Quintero, RD
Fact checked by Rosmy Barrios, MD
Last update: October 15, 2023
4 min read 2875 Views 0 Comments
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Fasting is considered an exceptional weight loss tool that not only fights stubborn fat but brings multiple benefits to your overall health. 

Those who follow an intermittent fasting lifestyle can benefit from normalized blood sugar, insulin levels, and a decreased risk of heart disease. 

Intermittent fasting entails food abstinence for extended periods. While simple, in theory, it can be difficult to adapt to a restricted eating pattern.

Aside from transitioning to a more conscious way of living, many people struggle with intermittent fasting side effects

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It’s common for dietary changes to affect bowel movements. Diarrhea during fasting, however, is one of the less common side effects of intermittent fasting.

This article discusses the link between diarrhea and fasting, possible causes, and other potential adverse effects. 

Diarrhea After Fasting: Is It Common?

While watery stools and diarrhea during fasting are relatively uncommon, some people do experience diarrhea when they break a fast. 

Diarrhea may occur after fasting periods if you don’t ease yourself out of the fast. 

During the fasting period, your body becomes extra sensitive to food. If you come out of your fast and binge eat junk food or foods you can’t digest easily, you can upset your stomach, causing diarrhea.

In most cases, intermittent fasting won’t directly cause diarrhea on its own. It’s more likely to occur when you break your fast. 

Be mindful about what you eat when your feeding window arrives, as your body needs a chance to return to its normal function. 

Other causes of diarrhea after fasting include:

  • Food poisoning 
  • Lactose intolerance 
  • Food allergy 
  • Medications 
  • Unhealthy diet
  • Too many caffeinated drinks
  • Zero-calorie sweeteners
  • Too many electrolytes

Usually, diarrhea is temporary. However, you should seek professional medical advice from your doctor immediately if your symptoms are severe or if you have blood or mucus in your stool.

Diarrhea can cause severe dehydration, which is especially dangerous while fasting. Drink plenty of water, and consider oral rehydration solutions that can hydrate your body quicker.

Why Does Not Eating Cause Diarrhea? 

Intermittent fasting can positively affect gut health, supporting the gut microbiome.

But when you stop eating, the digestive system slows down. 

When you’re fasting, your digestive system ultimately takes a break.

It can take time for the bowel to resume normal function, which may cause diarrhea in some people when they return to food consumption. 

It’s best to have small meals after a fasting routine to reset the digestive tract. Bone broth makes a great first meal as it is easy to digest on an empty stomach.

Can Drinking Too Much Water Give You Diarrhea?

While you must drink lots to avoid dehydration when intermittent fasting, too much water may cause diarrhea while fasting. 

When there is too much water in your body, it can play havoc with your kidneys as they can’t remove the excess water. This can trigger diarrhea and sickness.

Drinking too much can also disrupt your electrolyte balance. Low sodium may also trigger diarrhea. If your sodium levels become diluted, it can lead to hyponatremia, a potentially life-threatening complication.

What Are the Potential Side Effects of Fasting?

Intermittent fasting is an excellent way to burn fat, lose weight, and maintain a healthy diet. 

It’s not all plain sailing, though.

Not everyone will experience diarrhea during fasting, but some common adverse effects are associated with the method.

Here are some potential consequences to expect. 

#1 It can make you feel unwell

It’s not uncommon to feel unwell during an intermittent fast. 

Research suggests that people may experience headaches, fatigue, lethargy, low energy, and nausea after so many hours of fasting.

You may also feel hungry in the initial stages. 

Many of these symptoms can be attributed to low blood sugar. 

Often, these symptoms begin in the early days of fasting and subside as your body adapts to regular intermittent fasting. 

#2 Digestive discomfort

We’ve covered diarrhea during fasting, but bloating and constipation are more likely to occur from an intermittent fast. 

Digestive changes and bowel issues are often the results of a dietary change. 

Many people who use intermittent fasting combine it with a low-carb, high-fat diet. The body struggles to break down some high-fat foods, particularly saturated and trans fats, which can leave dieters experiencing diarrhea or the opposite – constipation. 

Dehydration also plays a role. Not everyone drinks enough water in the fasting window. It’s easy to forget to drink when you’ve cut out food.

Dehydration is a significant trigger for constipation, as the water supports regular bowel movements. Your diet may also lack fiber, an essential carbohydrate that keeps a healthy gut and prevents constipation. 

#3 Malnutrition 

If you don’t eat the right foods in your eating window, you risk missing out on essential nutrients. 

Malnutrition develops when you deprive your body of the vitamins and minerals it needs to function properly. 

If you’re going to try an intermittent fasting plan, it’s critical to eat a nutritious diet. Losing weight might be your priority, but you should never practice severe calorie restriction when fasting. 

Talk to your doctor about an IF plan that suits your health needs.

A Word From Our RD

Intermittent fasting might be the dieting plan that helps you lose weight.

It can provide you with health benefits, including more energy, improved brain function, and protection from insulin resistance.

Unfortunately, intermittent fasting has some potential adverse effects that most people will experience, like constipation, nausea, and headaches.

Diarrhea is rare when fasting, but some people may experience bowel issues after breaking a fast. This is because your bowels are inactive during fasting periods, and they need to resume function when you eat again.

To avoid upsetting your stomach, start by eating a small meal when you break your fast. Avoid greasy and refined foods, as you may be extra sensitive to such foods.

You can help treat diarrhea with some home remedies, but you may want to end your fast if diarrhea persists.

Any of the following symptoms require medical attention:

  • Severe abdominal pain
  • Bloody stools
  • Fever
  • Dizziness
  • Loss of consciousness


Is diarrhea normal when starting intermittent fasting? Mild diarrhea is usually only temporary, and there are many ways to treat it with home remedies. But if you are experiencing diarrhea while fasting, you may want to reconsider your fast. 

If other symptoms accompany your diarrhea, like dizziness, extreme weakness, vomiting, or blood in the stool, you must contact your doctor. 

Remember, intermittent fasting is not for everyone. Always prioritize your health and find a weight loss program that works for you.

Written by Edibel Quintero, RD
Edibel Quintero is a medical doctor who graduated in 2013 from the University of Zulia and has been working in her profession since then. She specializes in obesity and nutrition, physical rehabilitation, sports massage and post-operative rehabilitation. Edibel’s goal is to help people live healthier lives by educating them about food, exercise, mental wellness and other lifestyle choices that can improve their quality of life.
The article was fact checked by Rosmy Barrios, MD
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Written by Edibel Quintero, RD
Fact checked by Rosmy Barrios, MD
Last update: October 15, 2023
4 min read 2875 Views 0 Comments

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