Keto Diet Giving You The Runs? Here’s Why You Might Be Experiencing It  - Men's Health Magazine Australia

Keto Diet Giving You The Runs? Here’s Why You Might Be Experiencing It 

A number of people swear by the keto diet, but for others the high fat diet can be something of a toilet disaster.

Social media makes the keto diet look like fun. Scroll through the #keto tag on TikTok and you’ll find loads of keto recipes—sandwiches made with bell peppers instead of bread, cucumber dipped in stevia (which apparently tastes like watermelon, without the sugar), and keto “popcorn” made of cubed cheese—plus posts from folks that have had success following the high-fat, low-carb plan.

And sure, getting creative in the kitchen while working towards your health goals can be fun! But when certain keto side effects start popping up, that fun often comes to a screeching halt. You’ve heard about the keto flu and low-carb breath, but there’s another side-effect that people are less comfortable talking about: Keto diarrhea.

“It’s so bad that I can’t leave my house and I have stomach cramps constantly,” said one Redditor in a Keto Diarrhea thread.

“Last night in the middle of the night I had to run to the toilet,” wrote another redditor who was new to the keto diet. “This has continued all day today and it sucks to say the least.”

In the comments, there are other keto devotees telling the original posters to stick it out, and that it’s a normal part of starting keto for some people.

But, is keto diarrhea normal? What causes it? Is it forever? And, when should you take it as a sign to stop the diet or see your doctor? We have answers.

What is keto diarrhea?

Although keto diarrhea is a common side-effect, it’s not the same for everyone.

Often, keto diarrhea is actually steatorrhea, a specific type of diarrhea caused by too much fat in the stool, says Karie Cassell, R.D., a dietitian and the author of The Domino Diet. Steatorrhea is typically pale, foul-smelling and might be coated in a thick, greasy film.

It’s also possible that the keto diarrhea you’re experiencing is just regular diarrhea, characterized by loose, watery stools without excess fat content, Cassell says.

Some people experience keto diarrhea within the first few days of starting the diet, while others might start getting diarrhea weeks or months later, Cassell says.

What causes keto diarrhea?

High fat content

The main reason for keto diarrhea is the incredibly high fat content of the diet. Fat takes longer to break down in your body than carbs or protein.

When you suddenly start eating tons of fat, your digestive system can struggle to keep up. Some of the fat may be malabsorbed—not broken down properly and, thus, not completely absorbed by your body—and excreted in your poop.

This can lead to steatorrhea, stools that contain high amounts of fat and look like diarrhea, says Karie Cassell, R.D., a dietitian and the author of The Domino Diet.

Lack of fiber

Another cause of keto diarrhea is the sudden lack of fiber that comes with cutting your carb intake so drastically. “Fiber is used for constipation and so it can be confusing to think of low fiber intake as a culprit to diarrhea,” Cassell says. But insoluble fiber, the type that turns to gel when mixed with liquid, actually bulks your stools and helps prevent diarrhea, Cassell says.

Artificial sweeteners

Keto desserts can also be a cause of keto diarrhea. “Many artificial sweeteners like sugar alcohols are harder to digest,” Cassell says. If you’re eating lots of artificially sweetened desserts, it’s possible that they’ll give you an upset stomach followed by diarrhea.

Changes to your gut microbiome

If you’ve been on the keto diet for several weeks or months and you’re just starting to experience diarrhea, it could be due to unfavorable changes in your gut microbiome. Without fruits, vegetables, and other plant foods, you won’t be getting much prebiotic fiber. And without prebiotic fiber, the healthy probiotic bacteria in your gut won’t have the food they need to thrive. So, keto has the potential to worsen your digestive health overall by reducing the healthy bacteria in your microbiome. That can lead to increased frequency of diarrhea and other nasty side effects.

Does keto diarrhea last forever?

In most cases, no, keto diarrhea doesn’t last forever. If it’s just a matter of your digestive system getting used to breaking down all that fat, your stools could bulk up within a week or two. But, if your diarrhea is caused by changes in your microbiome, then it might be ongoing, Cassell says.

If you experience keto diarrhea for more than a week, Cassell suggests increasing your fiber intake (you can do this by adding non-starchy vegetables that are low in carbs) and eliminating any artificial sweeteners or sugar alcohols.

When should you see a doctor about keto diarrhea?

If your keto diarrhea (or any type of diarrhea) is severe and lasts more than two days, the Mayo Clinic recommends going to see your doctor. Frequent, ongoing diarrhea can lead to dehydration, which might show up as dry mouth, dizziness, excessive thirst, no urination or dark urine, or weakness.

And even if your keto diarrhea isn’t severe but doesn’t go away after the first few days, it might be time to rethink whether the diet is a good idea for you. No one wants to live life worrying about being within throwing distance of a toilet at all times.

This article was first published on Men’s Health US.


Christine Byrne, MPH, RD, LDN, is a registered dietitian and the owner of Christine Byrne Nutrition, a private practice serving clients in Raleigh, NC, and virtually across the country.

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