What Are the Stomach Issues on Keto Diet and How to Fix Them?

October 17, 2025 •

4 min read

Up to two-thirds of people report experiencing gastrointestinal issues during their first few weeks on a ketogenic diet. This initial discomfort, often called the 'keto flu,' can include common problems like constipation, diarrhea, and bloating. Knowing what are the stomach issues on keto diet and their causes is the first step toward managing them for a smoother transition.

Quick Summary

Many people on a ketogenic diet face digestive troubles as their bodies adjust to high fat intake and low fiber. Symptoms like constipation, diarrhea, and bloating are common due to shifts in gut bacteria and bile production. Solutions include boosting fiber intake with low-carb foods, staying hydrated, and monitoring MCT oil and sugar alcohol consumption.

Key Points

Initial Adaptation: The body's shift to a high-fat, low-carb diet can temporarily disrupt digestion, causing common issues like constipation or diarrhea.
Fiber Deficiency: A primary cause of constipation on keto is the elimination of high-fiber foods like grains and fruits.
Fat Malabsorption: Diarrhea can occur as the digestive system adjusts to processing a higher volume of fats, or from overconsuming MCT oil.
Gut Microbiome Shift: Changes in gut bacteria as they adapt to a low-carb environment can lead to gas and bloating.
Careful Supplementation: Many artificial sweeteners found in keto products can cause digestive distress and should be consumed in moderation.
Manage with Whole Foods: Prioritize keto-friendly whole foods that are high in fiber, such as avocados, seeds, and leafy greens, to support gut health.

Switching to a ketogenic diet can be a shock to your digestive system. With a drastic reduction in carbohydrates and a significant increase in fat, your body must adjust its metabolic processes. This change can manifest as a variety of uncomfortable stomach issues, which are typically temporary as your gut adapts.

Common Digestive Problems on Keto

The most frequently reported stomach issues on keto are opposite extremes: constipation and diarrhea.

Constipation

This is one of the most common complaints and is often caused by a sudden decrease in fiber. High-carb foods like grains, fruits, and legumes, which are rich in fiber, are largely eliminated on a keto diet. Fiber is essential for adding bulk to stool and promoting regular bowel movements. When fiber intake drops, the gastrointestinal tract can slow down, leading to fewer and more difficult bowel movements.

Diarrhea

Conversely, some people experience diarrhea, particularly when first starting the diet. This can happen for a few reasons:

Increased fat intake: The body's fat-digesting enzymes and bile may need time to ramp up production to handle the higher fat load. Undigested fat can travel to the large intestine, causing loose, watery stools.
MCT oil: Medium-chain triglyceride (MCT) oil is a popular supplement for ketosis, but it is rapidly digested and can cause abdominal cramps and diarrhea, especially when consumed in large amounts.
Sugar alcohols: Many keto-friendly processed foods contain artificial sweeteners like erythritol, sorbitol, and maltitol. These sugar alcohols are not easily absorbed and can have a laxative effect, leading to digestive distress.

Bloating and Gas

Changes in the gut microbiome can cause increased gas and bloating. As carb-loving bacteria starve and new fat-loving bacteria colonize, this bacterial shift can cause discomfort. Additionally, some high-fiber, low-carb vegetables common in keto, such as cauliflower and broccoli, are also high in FODMAPs (fermentable carbs) and can trigger gas in sensitive individuals.

Acid Reflux and Nausea

With a higher intake of fat, the stomach empties more slowly, which can contribute to acid reflux or heartburn. Nausea is also a classic symptom of the "keto flu" during the initial adaptation period as the body transitions into ketosis.

Management Strategies for Keto Digestive Issues

Here are practical steps to help alleviate stomach issues on a keto diet:

Gradual Transition: Instead of an abrupt change, consider easing into the diet by slowly reducing carbs and increasing fats over a few weeks. This gives your digestive system time to adapt.
Increase Keto-Friendly Fiber: Incorporate more fiber-rich, low-carb foods into your meals to promote regularity.
Stay Hydrated: Drinking plenty of water is essential for both constipation and diarrhea. It helps soften stools and replaces fluids lost from diarrhea, while also aiding electrolyte balance.
Monitor MCT Oil: If using MCT oil, start with a small amount and gradually increase the dose to assess your tolerance.
Check for Sensitivities: Be mindful of food sensitivities. Dairy products, nuts, and certain high-FODMAP vegetables can cause issues for some people. An elimination diet can help pinpoint triggers.
Consume Probiotics and Fermented Foods: Supporting your gut microbiome with probiotics and fermented foods like sauerkraut and kimchi can help restore balance and improve digestion.
Avoid Processed Keto Foods: Many processed keto-friendly snacks and bars contain sugar alcohols that can upset your stomach. Opt for whole, natural foods instead.

Comparing Temporary vs. Chronic Stomach Issues


Feature	Temporary Keto Adaptation Issues	Potential Chronic or Underlying Issues
Timing	Occur within the first few days or weeks of starting keto.	Persist for more than a few weeks despite management efforts.
Cause	Normal bodily adjustment to metabolic change, low fiber, or high fat.	Underlying conditions like gallbladder problems, IBS, or food intolerance.
Severity	Mild to moderate, resolves with time and minor adjustments.	Severe, persistent pain, bloody stools, or significant discomfort.
Action	Focus on hydration, increasing fiber, and easing into the diet.	Consult a doctor to rule out more serious medical conditions.

Keto-Friendly High-Fiber Food List

Avocados: 10 grams of fiber per cup.
Chia Seeds: 10 grams of fiber per ounce.
Flax Seeds: 3.8 grams of fiber per two tablespoons.
Leafy Greens: Spinach, kale, and arugula are low in carbs and high in fiber.
Broccoli & Cauliflower: Contain fiber, but may cause gas in some people.
Nuts: Almonds have 3.5 grams of fiber per ounce.

Conclusion

While the ketogenic diet can lead to temporary stomach issues like constipation, diarrhea, and bloating, these are often signs of your body adapting to a new metabolic state. By being mindful of your fiber intake, staying hydrated, and adjusting your consumption of fats and artificial sweeteners, you can successfully navigate these challenges. If digestive problems persist or become severe, it is always best to consult a healthcare professional to rule out any underlying medical conditions. With a thoughtful approach, it is possible to maintain a healthy gut while pursuing the benefits of a keto lifestyle.

For more in-depth information on managing the digestive side effects of a ketogenic diet, reputable resources like Medical News Today offer additional tips and advice.

Frequently Asked Questions

For most people, temporary digestive issues like bloating or nausea typically subside within a few days to a few weeks as the body adapts to ketosis. If symptoms persist longer than that, it is advisable to consult a healthcare professional.

Yes, Medium-Chain Triglyceride (MCT) oil is a common cause of digestive upset, including cramps and diarrhea, especially if taken in large doses at once. It's best to start with a small amount and gradually increase it as your body adapts.

Constipation is often a result of significantly reducing your fiber intake by cutting out high-carb foods like grains and fruits. To counteract this, you should increase your consumption of low-carb, high-fiber foods such as leafy greens, avocados, and chia seeds.

Diarrhea can occur because your body may struggle to produce enough bile and enzymes to digest the high fat content, leading to malabsorption. Additionally, excessive use of MCT oil or artificial sweeteners can cause loose stools.

To reduce bloating and gas, you can increase your intake of fibrous vegetables gradually, consume probiotic-rich fermented foods like sauerkraut, stay well-hydrated, and be mindful of consuming too many sugar alcohols.

You should consult a doctor if your symptoms are severe, include blood in your stool, involve constant or severe abdominal pain, or persist for more than a few weeks. These could be signs of an underlying issue.

Yes, keto-compliant fermented foods like sauerkraut and kimchi are rich in probiotics that can help support a healthy gut microbiome and improve digestion, which can alleviate some keto-related digestive issues.