Diarrhea After Fasting: Why It Happens and What to Do About It

For centuries, people have undertaken periods of fasting, be it due to their religious beliefs or because of its well-researched health and weight loss benefits.

Intermittent fasting (IF) has become the go-to for many aiming to improve their lifestyle, cognitive, and metabolic functions, leading to a growing number of doctors and dieticians suggesting we incorporate fasting into our daily routines.

However, aside from IF’s advantages, very few people discuss the possible side effects of intermittent fasting. Yet, like all diets, until your body adjusts to the changes in food and body function, fasting can cause unpleasant digestive issues, and diarrhea after intermittent fasting does affect some people.

If intermittent fasting diarrhea concerns you, here’s a look at intermittent fasting and diarrhea, why it happens, how long it usually lasts, and the best way to treat and deal with the condition.

Does fasting give you diarrhea?

First, the good news is that diarrhea is rarely caused by fasting alone, and it’s uncommon to experience diarrhea during fasting.

However, you may experience diarrhea during intermittent fasting following the meal that breaks the fast. In simple terms, loose bowel movements often result after eating too much food too quickly or if you eat the wrong foods on an empty stomach.

Many people look forward to the food they eat following the fast, and it’s easy to binge-eat your favorite meal or shock your system with high-fat or sugary foods after your fast, which can cause an upset stomach.

This is why it’s essential to track meal times and carefully consider the food you choose to break the fast if you want to avoid loose stools. This can easily be done with the help of Fasting Kompanion.

Why does intermittent fasting cause diarrhea?

As stated, intermittent fasting rarely causes diarrhea on its own, as your bowel function is limited when it’s not in use.

So why does intermittent fasting diarrhea happen?

To answer the question, let’s first understand what diarrhea is.

Diarrhea is a common condition most of us experience at certain points in our lives, and it is caused by the over-secretion of salts and water in the GI tract. This excess fluid leads to loose or watery bowel movements, which can be extremely unpleasant depending on how severe the condition is.

Diarrhea is most often triggered by what you eat and drink, although several other factors can also cause it.

The most common causes of diarrhea after fasting include:

• Caffeine: When fasting, you can enjoy black coffee, tea, and zero-calorie drinks throughout the day. However, diarrhea after breaking fasting can be caused by the excessive consumption of liquid, especially beverages containing caffeine, which is well known for its laxative properties.  
• Lactose intolerance: Food intolerances, most notably lactose or dairy intolerance, can cause digestive dysfunction.
• Fat: The excess bile amassed by consuming too much fat in your diet is a common cause of diarrhea, so it’s best to avoid fried or high-fat meals directly following your fast.
• Vitamins and supplements: High-dosage vitamins and supplements, such as vitamin C, magnesium, and medium-chain triglycerides (MTCs), can result in an upset stomach.
• Fructose: If you consume a large amount of fruit or fruit juice, this could trigger a bout of diarrhea due to the laxative qualities in fructose.
• Pre-existing conditions: Many digestive tract conditions like irritable bowel syndrome (IBS), ulcerative colitis, celiac disease, and Crohn’s disease are known to cause diarrhea.
• Antibiotics and prescription medications: Antibiotics and some other prescription medications often cause an upset stomach or other digestive issues.

Is diarrhea a side effect of intermittent fasting?

Embarking on any change in diet and nutrition can result in digestive issues, so diarrhea is listed as a side effect of intermittent fasting.

Gastrointestinal upset happens because the zero food and calorie intake over a prolonged period shocks your digestive system, causing it to function differently.

Digestive issues, including constipation, nausea, gas, bloating, and diarrhea, are symptoms you may encounter when starting on an intermittent fasting plan, especially if you follow a high-fat and protein diet, such as keto, in conjunction with intermittent fasting.

Dehydration is another side effect you need to monitor, which can result from diarrhea, so you must drink lots of water and remain hydrated during and after a fast.

How long does keto diarrhea last?

Many who embark on intermittent fasting combine their fasting with other diets like ketogenic to maximize their fat burn and weight loss results.

Although keto doesn’t technically cause diarrhea, keto intermittent fasting diarrhea may result due to higher levels of fat and protein consumed with the diet.

Most people who encounter digestive issues and gastrointestinal upset during fasting or when starting on a keto diet only do so for a few days or until their body gets used to digesting food in an entirely new way.

If your symptoms persist for over a couple of weeks, you should speak to your doctor or healthcare advisor.

How to stop diarrhea from intermittent fasting?

If you experience intermittent fasting diarrhea, several ways exist to ease the issue and prevent it from happening again.

The first and most important thing to do is to drink lots of water and stay hydrated, as diarrhea can cause dehydration, which is a potentially serious condition.

It is also a good idea to take a recommended dose of electrolytes that contain minerals like potassium, calcium, sodium, and magnesium to replace the minerals lost due to loose bowel movements and stomach upset.

Eat small, balanced, and easy-to-digest meals instead of large portions or foods that are high in fat or sugar. And be mindful of the food you eat to break the fast so you don’t shock your digestive system.

Also, avoid artificial sweeteners and caffeinated drinks like coffee and tea, as these are known to aggravate digestive issues.

If your intermittent fasting diarrhea continues for more than a few days, consider what you are eating and drinking and if you could have a food intolerance. If possible, try swapping out the diary for lactose-free alternatives and monitoring if there’s an improvement–food allergies are far more common than you think.

The upshot is if your digestive problems worsen or continue for over two weeks, it’s time to consult your healthcare provider.