Why the keto diet may lead to keto diarrhea


Your best friend did it. So did your neighbor and even your boss. They each tried out the keto diet. Heck, search Instagram or TikTok and everyone makes it look easy. So, you decided to give it a try from the tons of recipes to social media posts of everyone’s success stories. You knew some people will experience side effects such as keto breath and even the “keto flu” of symptoms like headaches, tiredness, brain fog and nausea.  But there was one side effect unmentioned – keto diarrhea.

Explaining keto diarrhea

Diarrhea is never a good thing. But, it’s even worse when you’re trying to stick to a diet plan. It makes for a rather crappy situation. 

The type of diarrhea associated with the keto diet is called steatorrhea.  Steatorrhea may happen if a person is eating too much fatty or greasy food which affects bowel movements having too high a fat content. As a result, steatorrhea stools are usually pale, oily, bulky, and foul-smelling. Not exactly what you may have expected from following the keto diet. 

However, stearrhea can result from a bile salt deficiency, a pancreatic enzyme deficiency, or a lymphatic obstruction. But if steatorrhea developed after starting the keto diet, the diarrhea is likely because of your dietary change.

What causes keto diarrhea?

A hardcore keto diet typically has a macronutrient ratio of 5% carbohydrates, 25% protein, and 70% fat. This dietary ratio forces the body into a state called ketosis. 

Ketosis is when there are not enough carbohydrates to breakdown into the sugar glucose to provide energy to body cells – our cells prefer using glucose for energy. Carbohydrates are typically our main source of energy for muscles cells and the brain. Without sufficient carbohydrates in the diet, this forces the body to start burning fat producing ketone bodies, substances the body makes when carbohydrates are not available. Ketone bodies are considered an alternative source of energy that occurs when a person is in ketosis. 

The weight loss from following a keto diet is the state of ketosis is forcing the body to switch its fuel source. Instead of using glucose from eating carbohydrates, the body turns to the liver to break down stored fat called ketone bodies.  

To force the body to use stored fat as fuel, severely limiting carbohydrates of less than 50 grams per day, results in ketosis of using fat stores as the main source of energy. When a person begins a keto diet, it generally takes two to four days to reach ketosis. However, this state of dietary restriction can also result in the side effect of keto diarrhea. 

Causes of keto diarrhea


  • High fat diet


The primary cause of keto diarrhea is following a high fat diet. The body is not able to break fat down as it can carbohydrates. When consuming high amounts of fat, the digestive system has difficulty keeping up because fat is broken down slowly. When this happens, some fat is not completely broken down thus unabsorbed and instead is excreted in your stools, which leads to steatorrhea.  Bowel movements will be runny like diarrhea.

  • Lack of fiber

Fiber is a carbohydrate and is found only in plant based foods – no animal based food contains fiber. Since the keto diet significantly restricts carbohydrates – the only source of fiber – a lack of fiber leads to constipation. While constipation and diarrhea are opposites, a low fiber intake can also lead to diarrhea. That’s because insoluble fiber is necessary for bulking up stools preventing diarrhea. 

Another cause related to lack of fiber is that many keto desserts use artificial sweeteners such as sugar alcohols that are difficult to digest. Some people are sensitive to sugar alcohols and if eating lots of artificially sweetened desserts, may notice an upset stomach followed by diarrhea.

  • Gut microbiome changes

People who have followed the keto diet long term (weeks or months) may experience diarrhea down the road. This may be attributed to changes in the gut microbiome. When healthy carbohydrates such as fruits, vegetables, beans, and whole grains are strictly eliminated, you eliminate prebiotic fibers. Prebiotic fibers are necessary for healthy gut functioning and without it, gut health will suffer such as increased diarrhea.

Seeking help for keto diarrhea

Diarrhea of any cause should be seen by a doctor if lasting more than two days. Diarrhea that is frequent and ongoing can quickly lead to dehydration.  Signs of dehydration include excessive thirst, little to no urination or dark urine, dry mouth, weakness, and dizziness. 

Even if keto diarrhea is mild, if lasting for several days, you may want to consider following a healthier way of losing weight. Long-term, the keto diet is difficult to follow many people find it unsustainable. A better way of losing weight is to follow a dietary plan that allows you to eat all food groups and emphasizes exercise. This is likely to be a better way of achieving a healthy body weight. 


Dr. David Samadi is the Director of Men’s Health and Urologic Oncology at St. Francis Hospital in Long Island. He’s a renowned and highly successful board certified Urologic Oncologist Expert and Robotic Surgeon in New York City, regarded as one of the leading prostate surgeons in the U.S., with a vast expertise in prostate cancer treatment and Robotic-Assisted Laparoscopic Prostatectomy.  Dr. Samadi is a medical contributor to NewsMax TV and is also the author of The Ultimate MANual, Dr. Samadi’s Guide to Men’s Health and Wellness, available online both on Amazon and Barnes & Noble. Visit Dr. Samadi’s websites at robotic oncolo gy and prostate cancer 911. 

Why the keto diet may lead to keto diarrhea
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Dr. David B. Samadi