There are many health benefits of intermittent fasting, including balanced blood sugar, reduced blood pressure, and a decreased risk of heart disease. While some people experience side effects during fasting, diarrhea isn’t usually one of them.
If you experience diarrhea during fasting, there may be an underlying cause behind your symptoms. This guide covers those causes, whether or not you should worry, and how you can prevent diarrhea during prolonged fasting.
Does Fasting Cause Diarrhea?
There is usually an underlying cause for diarrhea while fasting outside of the fast itself. Diarrhea happens when food moves too quickly through your digestive system. Because you aren’t eating, there’s no food in your digestive tract, which makes it unlikely that you’ll have diarrhea.
That means it’s not normal to have diarrhea on an empty stomach, and you’re more likely to have unusual bowel movements and diarrhea after fasting.
This is especially true after multiple days of fasting. Your digestive system slows down when you stop eating. If you eat a large, rich meal right after a long fast, your digestive system may not be able to digest it, causing diarrheaPotential Causes
Fasting doesn’t usually cause diarrhea directly. Here are a few possible causes of diarrhea during fasting:
- Electrolyte imbalance: Many people like to take electrolytes or supplement with ketone drinks during fasting periods to help prevent dehydration. If you take too many, you may excrete them with excess water through your gastrointestinal tract, causing diarrhea.
- Caffeine: Coffee and other caffeinated drinks are popular during fasts because they contain no calories and may suppress your appetite. Caffeine also increases bowel motility, leading to faster passage of food and water through your intestines. (1)
- Zero-calorie sweeteners: Aspartame, sucralose (Splenda), and sugar alcohols (erythritol and xylitol) can be difficult for the digestive system to absorb. This can lead to digestive distress, including diarrhea, bloating, and abdominal discomfort. (2)
- Poor diet: A diet high in processed or fatty foods can disrupt your gut health. Once fasting begins, digestive issues like diarrhea can occur as the body takes some time to adjust to a fasting state.
- Food intolerances: Food sensitivities like lactose intolerance can cause diarrhea if you consume any food triggers just before fasting periods.
- Mineral deficiencies: A lack of essential minerals, like magnesium or zinc, can impair digestive function and result in chronic diarrhea. (3) It can also worsen symptoms of gut conditions like irritable bowel syndrome (IBS).
- Inflammatory bowel disease (IBD): Diarrhea is a common symptom of ulcerative colitis and Crohn’s disease, the most common type of IBD. While fasting can reduce inflammatory markers in the body, talk to a doctor before starting a fast if you have IBD. (4)
- Infection: Food poisoning or gastroenteritis can cause diarrhea even during fasting as your body responds to infection.
- Medication allergies: Much like food sensitivities, consuming certain medications just before fasting can trigger an allergic response, including diarrhea.
Following a keto diet can also cause changes to bowel movements for a short period of time, especially at the start. This can happen due to low digestive enzymes, too little fiber, or the overuse of medium-chain triglycerides (MCTs).
MCTs and MCT oils are great, but you should work your way up from a teaspoon at a time to avoid unpleasant side effects. Our high-quality MCT Oil Powder contains 7g of MCTs to boost ketones as you cut carbohydrates and curb hunger.
Side Effects to Watch For
Diarrhea during fasting can cause severe dehydration. When you fast, you lose several pounds of water weight. This happens because your body is burning through glycogen (sugar) stores, which releases water. (5)
As a result, you’re at risk of being dehydrated. When fasting, increase your water intake to ensure you’re getting enough water.
Diarrhea causes dehydration, too, and diarrhea during fasting can dehydrate you to dangerous levels. Watch for the following symptoms:
- Blurry vision
- Dry mouth
- Dizziness
- Nausea
- Headache
- Cramping
- Bloating
Preventing and Treating Diarrhea
There are a few things you can do to prevent diarrhea during fasting:
- Drink lots of water.
- Take electrolytes like magnesium, sodium, calcium, and potassium at recommended doses, as excess electrolytes can cause diarrhea.
- Avoid caffeine from coffee, tea, and energy drinks.
- Avoid zero-calorie sweeteners like aspartame, sucralose, erythritol, and xylitol.
- Identify and skip foods you’re sensitive to, like lactose or gluten, before starting a fast.
- Eat a balanced diet before and after fasting periods.
- Consider taking probiotic supplements or eating probiotic-rich foods between fasts to support healthy gut bacteria. (6)
How to stop diarrhea from intermittent fasting comes down to the root cause of your digestive distress, but here are a few treatment options that can help:
- Rest. Exercise is great, but if you’re actively dealing with diarrhea, physical activity can exacerbate your symptoms and worsen dehydration. (7)
- Sip herbal teas. While you should continue to drink water if you have diarrhea, non-caffeinated herbal teas like chamomile or peppermint can soothe the digestive tract.
- Consider over-the-counter medications. Common medications like loperamide (Imodium) and bismuth subsalicylate (Pepto-Bismol) may reduce your symptoms.
- Take a break from fasting. If the diarrhea persists, end the fast and reintroduce bland, easily digestible foods.
- Talk to your doctor. If your diarrhea is severe or lasts more than a few days, talk to a physician to prevent severe dehydration and other complications.
When to Stop a Fast
Diarrhea alone is not necessarily a cause for concern as long as you drink plenty of fluids.
However, chronic diarrhea may be a symptom of a bigger digestive issue. If it persists for multiple days, stop fasting and visit your doctor.
You should also stop fasting and see a doctor as soon as possible if you have any of the following symptoms:
- Severe abdominal pain
- Fever
- Bloody stools
- Loss of consciousness
- Persistent fatigue
These symptoms could be a sign of a more serious health issue.
The Takeaway
While diarrhea isn’t one of the common side effects of fasting, it can happen to some people. Hydration, underlying health conditions, and diet can all impact bowel movements during fasting.
By and large, intermittent fasting can be a valuable tool for weight loss and overall wellness. It can also help you re-enter ketosis, and most people fast on keto with few to no side effects.
The most important thing is to take steps to prevent dehydration — that means drinking lots of water! — and watch your symptoms.
FAQ
How can I manage diarrhea while on a liquid fast?
If you get diarrhea in the middle of a water fast (when you’re having only water, no food), you should end your fast immediately.
This is different from a liquid diet to manage certain medical conditions or to heal after a medical procedure. In that case, clear liquids may include broth, diluted juices, plain gelatin, herbal teas, and electrolyte drinks.
If you get diarrhea in this scenario, boost your water intake. Reintroduce bland, easily digestible foods if symptoms persist.
How does intermittent fasting work?
Intermittent fasting involves cycling between periods of eating and fasting, allowing the body to shift from using glucose (from food) for energy to burning stored fat. This metabolic shift encourages the body to enter a state of ketosis, where fat is converted into energy.
Intermittent fasting can improve insulin sensitivity, aid weight loss, and promote cellular repair. For those on a keto diet, the eating pattern is used by some as a strategy to re-enter ketosis after consuming excess carbs.
How do I counter the digestion issues experienced after intermittent fasting?
When you break your fast, avoid overeating. Eat a small, easy-to-digest meal instead of a heavy or high-fat one, or try bone broth to prevent GI tract symptoms. A small meal will stimulate your digestive system and should bring it back to full function.
Stay hydrated, include probiotics to support gut health, and monitor your fiber intake until your digestion stabilizes and your gut feels like it’s back to normal.