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Diarrhea After Fasting: Causes, Solutions, & Prevention

6 min read
a woman is feeling sick, holding her stomach, diarrhea after fasting
Melissa Mitri post Reviewer Melissa Mitri post Reviewer
Verified by Melissa Mitri
MS, Registered Dietitian, Former President of CT Academy of Nutrition & Dietetics

Does fasting cause loose stools? Read on to learn whether it is normal to get diarrhea after fasting and what you can do with it immediately.

Table of Contents

Intermittent fasting has gained popularity as an effective method of shedding pounds. In addition to weight loss, it has been proven to bring about numerous health benefits [1]

However, as with any other dietary intervention, intermittent fasting can lead to certain side effects in some—especially in the initial phases. Diarrhea after fasting is one such side effect that you might have experienced. 

Can intermittent fasting cause diarrhea, and is it normal to get diarrhea after fasting? Today, we are going to answer these questions and discuss how you can treat—or better yet, prevent fasting-related diarrhea. 

Is it Normal to Get Diarrhea After Fasting?

There is almost no scientific data that links intermittent fasting and diarrhea, which hints that diarrhea is not a normal side effect of fasting.

However, a few people report that they experience episodes of diarrhea after intermittent fasting, which can make fasting quite an ordeal. 

While diarrhea while fasting is not an uncommon occurrence, it’s not a universal phenomenon either. It’s also not a reason to quit intermittent fasting altogether. 

Diarrhea is more likely your body’s way of reacting while it’s getting used to the new eating regime. For most people, diarrhea happens not during fasting but after they have had their first meal that breaks the fast. 

Several factors, including meal composition, hydration levels, and coffee intake, can be the cause of loose stools after fasting. 

Does Fasting Cause Diarrhea?

The short answer to this question would be no. Fasting does not directly cause diarrhea. 

Nevertheless, it conditions your digestive system in a way that makes it more prone to diarrhea. While you’re fasting, your digestive system slows down, and if you break your fast with foods that take a lot of effort to digest, it might cause digestive issues such as diarrhea.

6 Causes for Diarrhea After Fasting

Here are a few reasons that can trigger diarrhea after fasting:

1. You Chose The Wrong Foods To Break Your Fast With

As we mentioned just now, your digestive system is at rest after fasting for several hours. Foods that are hard to digest (such as high-fat, high-fiber food) can place a lot of strain on your digestive system. 

When fatty foods are not properly digested, they can stimulate the colon to secrete excess fluids and cause diarrhea. Some people also might get diarrhea after eating spicy foods [2]

2. It Could Be Certain Sugars Or Sugar Alternatives In Your Diet

High amounts of fructose have been linked to diarrhea as well as artificial sweeteners such as sugar alcohols [2]

3. You Might Have Consumed Too Much Coffee

Since you know you’re allowed to drink zero-calorie beverages like coffee during fasting, you might have reached for the coffee pot more often than recommended. Coffee is a natural laxative that can stimulate your bowel function [3], and drinking too much can result in multiple trips to the bathroom.

4. It Could Be Your Supplements

Some supplements, such as Vitamin C [4] and magnesium [5], can induce diarrhea if taken in high doses. 

5. You Might Be Drinking Too Much Water

While it is important to keep hydrated while you’re fasting, drinking too much water can cause electrolyte imbalances that can result in diarrhea [6].

6. Your Medications Can Be The Cause Of Diarrhea

Certain medications you’re taking, such as antibiotics and antacids, can cause diarrhea [7].

Why You May Have Diarrhea After Breaking Fast

The most likely reason to have diarrhea after breaking your fast is that your digestive system can’t handle the meal you eat immediately after fasting.

After being inactive for hours, your body needs time to start digesting food again. Because of this, you’ll want to carefully choose the foods that are easy to digest as the first meal after fasting.  

Eating large meals or fatty meals that are hard to digest immediately after fasting might lead to loose stools. 

Can Eating Once a Day Cause Diarrhea?

As we already explained, fasting does not cause diarrhea, nor does eating once a day. While eating once a day might lead to stomach discomfort due to bouts of hunger, it is not a likely cause of diarrhea. 

Diarrhea After Fasting: What to Do Right Away

If you experience loose stools after fasting, there are some immediate treatments you can try at home.

  • Evaluate your food, medication, and supplement intake to see if you can identify the culprit.
  • Drink lots of fluid (preferably an oral rehydration solution) to maintain proper hydration levels.
  • Try an over-the-counter anti-diarrheal medication such as Loperamide (Imodium) [8].

Most of the time, diarrhea is self-limiting and goes away within a few days. However, if the condition persists for longer than that and seems to worsen, you should consider consulting a doctor. 

Additionally, if you notice blood in your stools or are experiencing other symptoms such as fever, it’s best to seek medical support. 

Prevent Upset Stomach While Fasting

You can prevent an upset stomach while intermittent fasting by keeping an eye on your diet.

Eat A Simple, Bland Meal The First Thing After Fasting

Go for easy-to-digest foods like crackers, toast, and soup to break your fast. 

Eat Small, Frequent Meals

Small meals allow your stomach to adjust and thus slowly stimulate your digestion.

Keep An Eye On Your Coffee Intake

Coffee can trigger bowel movements, so keep an eye on your coffee intake during your fasting window as well as the eating window.

Keep Yourself Sufficiently Hydrated

Hydration during fasting is important, but don’t drink too much water as it can lead to electrolyte imbalances that can cause loose stools. The average daily fluid recommendation for men is 15.5 cups (3.7 liters), and for women, 11.5 cups (2.7 liters) per day [9]. For more personalized recommendations, consult with a registered dietitian.

Take Note Of The Medications And Supplements You Are Taking

Ask your doctor if the supplements and medications you take can lead to an upset stomach. Discuss with them about changing the medication schedules if they are likely to cause diarrhea after fasting. 

Final Words

  • Some people might experience diarrhea after fasting, but there’s no scientific evidence that links intermittent fasting and loose stools.
  • However, meals, medications, and supplements you take during and after fasting can cause loose stools and frequent bowel movements after fasting.
  • Eating easily digestible meals to break the fast, having small meals frequently, and limiting coffee intake can relieve diarrhea after fasting.
  • It is important to stay adequately hydrated during fasting as well as during episodes of diarrhea. 
  • If diarrhea symptoms don’t go away or improve after a couple of days, it’s best to consult your healthcare provider.
Disclaimer This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!

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