Understanding the Link Between Low Carb Diets and Diarrhea

Low carb diets, such as the ketogenic diet, have gained popularity for their potential to promote weight loss and improve certain health markers.

However, these diets can also lead to gastrointestinal issues, including diarrhea. This article aims to provide an in-depth understanding of why this happens and how to manage it.

What is a Low Carb Diet?

A low carb diet, like the ketogenic diet, is a dietary approach that emphasizes high fat, moderate protein, and very low carbohydrate intake. The primary goal is to induce a metabolic state known as ketosis, where the body uses fat instead of glucose as its primary energy source 1.

While this diet has been linked to weight loss and improved blood sugar control, it can also lead to certain side effects, including diarrhea 2.

Why Does a Low Carb Diet Cause Diarrhea?

Several factors contribute to the occurrence of diarrhea when following a low carb diet:

1. High Fat Intake

Low carb diets, such as the ketogenic diet, require a high intake of dietary fats. This is because the body, in the absence of sufficient carbohydrates, turns to fats as its primary energy source.

However, the digestion of fats is a complex process that requires the liver to produce bile. Bile emulsifies fats, breaking them down into smaller droplets that can be more easily digested by enzymes in the small intestine.

When the intake of dietary fats increases significantly, the liver is prompted to produce more bile. Bile, in addition to its role in fat digestion, also has a natural laxative effect. It stimulates the muscles in the large intestine, accelerating the transit of waste through the digestive tract. This accelerated transit can result in loose, watery stools or diarrhea.

2. Changes in Gut Microbiota

The gut microbiota refers to the community of microorganisms, including bacteria, viruses, and fungi, living in our digestive tract. These microorganisms play a crucial role in our health, aiding in digestion, immune function, and even mental health.

A sudden change in diet, such as shifting to a low carb, high fat diet, can disrupt this delicate ecosystem. High-fat diets may cause inflammation in the digestive tract, decrease the production of beneficial short-chain fatty acids like butyrate, and lead to unfavorable changes in the composition of the gut microbiome 3.

For instance, a high-fat diet may promote the growth of certain bacteria that are more efficient at extracting energy from fats, but these bacteria might also be associated with inflammation and intestinal discomfort. These changes in the gut microbiota can potentially lead to diarrhea.

3. Artificial Sweeteners and Sugar Alcohols

In an effort to reduce carbohydrate intake, many people on a low carb diet turn to artificial sweeteners and sugar alcohols as low-carb alternatives to sugar. These include substances like aspartame, sucralose, and xylitol 4.

However, these substances are not fully absorbed in the digestive tract. When consumed in large amounts, they can draw water into the intestines, a process known as osmotic diarrhea. Additionally, they can be fermented by gut bacteria, producing gas and leading to bloating, cramping, and diarrhea.

4. Decreased Fiber Intake

Low carb diets often limit the intake of fruits, vegetables, and whole grains, which are primary sources of dietary fiber.

Fiber is a type of carbohydrate that resists digestion in the small intestine and reaches the colon relatively intact 5. There, it adds bulk to the stool and aids in its passage through the digestive tract.

high fiber food

A sudden decrease in fiber intake can disrupt this process. Without sufficient fiber, stools may be less bulky and pass through the digestive tract too quickly, resulting in loose stools or diarrhea. Furthermore, fiber also feeds beneficial gut bacteria, so a decrease in fiber intake can further disrupt the gut microbiota, potentially exacerbating diarrhea.

How to Manage Diarrhea on a Low Carb Diet

While diarrhea can be an uncomfortable side effect of a low carb diet, there are several strategies to manage this condition:

Increase Fiber Intake

Incorporating more low-carb, high-fiber foods into your diet can help manage diarrhea. Fiber adds bulk to your stool and can help regulate bowel movements.

Leafy greens, broccoli, avocados, chia seeds, and flaxseeds are examples of foods that are both low in carbs and high in fiber.

These can be easily incorporated into meals or snacks, helping to increase your fiber intake without adding too many carbs to your diet.

Stay Hydrated

Diarrhea can lead to dehydration due to the loss of fluids and electrolytes. It’s crucial to ensure you’re drinking enough water throughout the day. In addition to water, consider incorporating sugar-free electrolyte beverages to replace lost electrolytes. These beverages can help replenish electrolytes like sodium and potassium, which are essential for maintaining fluid balance in the body.

Limit Artificial Sweeteners

Artificial sweeteners and sugar alcohols, while low in carbs, can exacerbate diarrhea. These substances can draw water into the intestines or be fermented by gut bacteria, leading to loose stools. Try to limit your intake of these substances, opting for natural sweeteners like stevia or monk fruit, which are less likely to cause digestive issues.

Gradual Dietary Changes

A sudden shift to a low carb diet can be a shock to the system, potentially leading to digestive issues like diarrhea. Instead of making a drastic change, consider gradually reducing your carb intake and slowly increasing your fat intake. This approach can give your body and gut microbiota time to adjust to the new diet, potentially reducing the likelihood of diarrhea.

Probiotics and Prebiotics

Probiotics are beneficial bacteria that can support gut health, potentially helping to manage diarrhea. Probiotic-rich foods like yogurt, kefir, sauerkraut, and kimchi can be incorporated into your diet 5. Alternatively, you might consider taking a probiotic supplement.

Prebiotics, on the other hand, are a type of fiber that feeds the beneficial bacteria in your gut. Prebiotic-rich foods, such as asparagus, onions, and garlic, can help nourish your gut bacteria, promoting a healthy gut microbiota.

Limit Dairy Intake

Dairy products are often consumed in larger quantities on a low carb diet due to their high fat and low carb content. However, some people may have a low tolerance or intolerance to dairy, which can lead to digestive issues like diarrhea. If you suspect dairy may be contributing to your diarrhea, try reducing your intake or opting for lactose-free or non-dairy alternatives.

Remember, it’s important to listen to your body and make dietary adjustments that suit your individual needs. If diarrhea persists despite these changes, it’s advisable to seek medical attention.

When to Seek Medical Attention

While mild and temporary diarrhea can be a common side effect of transitioning to a low carb diet, it’s important to recognize when medical attention is necessary.

Severe Diarrhea

If you experience severe diarrhea, characterized by multiple episodes of loose, watery stools in a day, it’s crucial to seek medical attention. Severe diarrhea can lead to rapid dehydration, which can be life-threatening if not promptly addressed. Symptoms of dehydration include extreme thirst, dry mouth, fatigue, dizziness, and decreased urination.

Persistent Symptoms

If your diarrhea persists for more than a week, it’s important to consult a healthcare professional. Chronic diarrhea can lead to significant loss of essential fluids and electrolytes, which are vital for normal body functions. Over time, this can result in electrolyte imbalances, which can affect heart rhythm and overall health.

Chronic diarrhea can also lead to nutrient deficiencies. When food passes too quickly through the digestive tract, your body may not have enough time to absorb all the nutrients, leading to deficiencies that can impact various aspects of health, from energy levels to immune function.

Other Symptoms

In addition to diarrhea, if you experience other symptoms such as blood or mucus in your stool, severe abdominal or rectal pain, unexplained weight loss, or signs of dehydration, it’s important to seek medical attention immediately. These symptoms could indicate a more serious underlying condition that needs to be addressed.

Before Making Significant Dietary Changes

Before making significant dietary changes, such as switching to a low carb diet, it’s always advisable to consult with a healthcare professional. They can provide personalized advice based on your current health status, medical history, and nutritional needs 6. They can also monitor your health as you transition to the new diet and provide guidance on how to manage potential side effects, including diarrhea.

Remember, while a low carb diet can offer certain health benefits, it’s not suitable for everyone. Always prioritize your health and wellbeing, and don’t hesitate to seek medical attention when needed.


While low carb diets can offer certain health benefits, they can also lead to gastrointestinal issues like diarrhea.

By understanding the potential causes and implementing dietary strategies, you can manage these side effects and continue to reap the benefits of your diet. As with any diet, it’s important to ensure it’s well-balanced and suitable for your individual health needs. Always consult with a healthcare professional or dietitian for personalized advice.


  1. https://www.nature.com/articles/ejcn2013116
  2. https://www.tandfonline.com/doi/full/10.1080/17446651.2018.1523713
  3. https://www.nature.com/articles/nature12820
  4. https://www.nature.com/articles/1602532
  5. https://www.tandfonline.com/doi/full/10.1080/19490976.2017.1290756
  6. https://www.acpjournals.org/doi/10.7326/0003-4819-140-10-200405180-00006

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