Can Intermittent Fasting Affect Your Stool?

Can Intermittent Fasting Affect Your Stool?

Written by Andrew Brewer. ⚕️Reviewed and fact checked by our medical team.

Can Intermittent Fasting Affect Your Stool?

Intermittent fasting can have ripple effects across your entire lifestyle. You’ll start to feel better holistically, lose weight, improve your sleep, and so much more.

But, because you’re changing the frequency of what you put into your body, what comes out of it may also change. Here’s all you need to know about what intermittent fasting does to your stool.

Key Takeaways

  • Changes in stool can occur during intermittent fasting due to dietary adjustments and restrictions on calorie intake. Constipation is a common issue resulting from insufficient fiber and water intake, leading to bloating and discomfort.
  • Diarrhea can also occur during intermittent fasting, usually as a result of medication taken on an empty stomach or the discovery of food intolerances. Lactose intolerance is a frequent cause of diarrhea during fasting.
  • Consistent constipation or diarrhea should not be a regular occurrence during intermittent fasting. As the body adjusts and individuals learn what works for them, these episodes should diminish.
  • To avoid changes in stool, it is important to consume an adequate amount of fiber during the eating window. Aim for 25 to 30 grams of fiber per day to promote healthy bowel movements.
  • Staying hydrated is crucial for passing healthy stools. Aim to drink 3 to 4 liters (or about 100 to 135 oz) of water per day, as dehydration can lead to difficulty in having bowel movements and may even cause pain. Black coffee can also have a stimulating effect on bowel movements, but it should be consumed without additives to avoid breaking the fast.


Any change in your diet can cause changes in your bowel movements, and that includes participating in intermittent fasting plans. Even though there are no restrictions on what you can eat, people often make adjustments in their diets to promote additional weight loss.

The two biggest causes for constipation during intermittent fasting are that you’re not eating enough fiber or drinking enough water. These two combined factors lead to painful bloating and constipation. You’re trying to reduce your caloric intake, but by doing so, you may be reducing the nutrients you need to have healthy stools.


While this is less common, some people also find that they get diarrhea when they are intermittent fasting. This often has less to do with the intermittent fast itself and, again, more with what you’re putting in your body.

Some medicine, when taken on an empty stomach, can cause gastrointestinal issues like diarrhea. Additionally, as you adjust your eating habits during your eating windows, you may uncover intolerances that you didn’t know you had. The most common cause of diarrhea during intermittent fasting is lactose intolerance.

Pay attention to the context when you have a bout of diarrhea and try to uncover if you may have done something to cause it unintentionally. As you wait for the episode to pass, make sure that you drink enough water. You don’t want to get dehydrated, which can lead to constipation.

How to Avoid Changings in Stool

You shouldn’t worry about consistent constipation or diarrhea when intermittent fasting. As your body adjusts and you learn what works for you, these episodes shouldn’t be a regular occurrence. Here are some steps you can take to avoid them.

Eat More Fiber

Be more intentional about the food that you’re putting in your body, and that includes the amount of fiber in your diet. In general, you should be eating between 25 to 30 grams of fiber per day, so make sure that you pack it in during your eating window. This will help your stool be bulky enough to pass through your system.

High-fiber foods also have the added benefit of helping you feel fuller longer, so it’s a win-win to integrate these into your daily routine.

Drink More Water

Staying hydrated goes hand in hand with eating more fiber when it comes to passing healthy stools. If you are dehydrated, you will have a difficult time having bowel movements, and they may even be painful. Aim to drink 3 to 4 liters (or about 100 to 135 oz) of water per day.

Drinking enough water will also help prevent some of the hunger cues, tricking your body into thinking it’s full during your fasting windows.

Drink Some Coffee

Black coffee can also help you go to the bathroom, sometimes in as little as a few minutes from drinking! Just keep in mind that it should be black in order to not break fast. Some intermittent fasting plans will allow zero-calorie sweeteners, but others do not, as they can trigger a metabolic response in the body.

So How Does Intermittent Fasting Impact My Stool?

On its own, intermittent fasting will not impact your stool. It’s the changes you make as a result of the fast that can cause differences in the stool. Make sure you eat fiber and drink enough water to prevent getting constipated during intermittent fasting.


  • Does intermittent fasting always lead to changes in stool?

No, intermittent fasting itself does not directly impact your stool. However, the dietary adjustments and changes in nutrient intake that often accompany intermittent fasting can cause changes in bowel movements.

  • Why does intermittent fasting sometimes cause constipation?

Constipation during intermittent fasting can occur due to insufficient fiber and water intake. When calorie intake is reduced, it’s important to ensure you’re still getting enough fiber to maintain healthy stools.

  • Can intermittent fasting cause diarrhea?

While less common, intermittent fasting can occasionally lead to diarrhea. This is typically caused by factors such as medication taken on an empty stomach or the discovery of food intolerances, such as lactose intolerance.

  • Will I experience consistent constipation or diarrhea while intermittent fasting?

Consistent constipation or diarrhea should not be a regular occurrence during intermittent fasting. As your body adapts to the fasting schedule and you learn what works best for you, these issues should diminish.

  • How can I prevent changes in stool during intermittent fasting?

To avoid changes in stool, it is recommended to consume an adequate amount of fiber during your eating window. Aim for 25 to 30 grams of fiber per day. Additionally, staying hydrated by drinking enough water (3 to 4 liters per day) is important for maintaining healthy bowel movements. Avoiding triggers like medication on an empty stomach and uncovering any food intolerances can also help prevent diarrhea.

Andrew Brewer

Andrew Brewer

Andrew Brewer started to give people the guidance that he never received when he was first starting. His goal is to make your goals achievable and to offer you only the best fasting apps that the internet has to offer. You're not on your own - Andrew and the entire family of reviewers at are here with you every step of the way!