Everything You Could Possibly Want to Know About Keto Diarrhea

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Thinking about going keto? You may also want to think about one unfortunate side effect.

First things first, the keto diet is a low-carbohydrate, high-fat diet that has gone mainstream in recent years, says Johna Burdeos, a registered dietitian.

“The basic idea behind the keto diet is to restrict carb intake so that the body switches from burning glucose (sugar) for energy to burning fat, including stored body fat and dietary fat,” she says, noting that this shift in metabolism is known as ketosis.

Juliana Tamayo, M.S., R.D., an editor for FitnessClone and a clinical dietitian in Washington, D.C., echoes Burdeos, sharing that the ketogenic diet focuses on consumption of more fat and protein with very little carbohydrate."

The idea is helping your body switch from using carbohydrates for energy to using fat in a process called ketosis,” she says. “This way, your body will effectively burn fat for energy, which can lead to weight loss.” (Again, that process of burning fat for energy instead of glucose is called ketosis, hence the name “the keto diet.”)

As Tamayo and Burdeos both highlight that the keto diet may have some benefits like improved blood sugar control and weight loss. Still, some expert sources such as Mayo Clinic, are skeptical that it can help with long-term weight loss.

Despite the obsession and popularity going keto has these days, it’s not all buff muscles and beef. “...the keto diet has drawbacks, and one of the most common side effects experienced by people who follow the diet is keto diarrhea,” says Burdeos. “This condition is characterized by loose, watery stools and can occur as a result of several factors, including an increase in fat intake, a decrease in fiber intake, and changes in gut bacteria.”

There are other potential bathroom issues to be had when you go keto: Tamayo notes that constipation can be another problem for those who adhere to this way of eating due to the lack of fiber from vegetables and whole grains. She also links the keto diet to diarrhea because “the artificial sweeteners and sugar alcohols in many keto products can lead to [the condition].”

Another reason for keto diarrhea, says Tamayo, is the time that it takes your body to adjust to digesting high amounts of fat, which can lead to slight malabsorption diarrhea that usually resolves with time.

As Burdeos explains, fat is typically harder to digest compared to protein and carbs, and takes longer as well. “When you follow the keto diet, you're likely to consume a greater amount of fat than you normally would've to get your calories in and compensate for restricting carbs,” she says.

What’s more, offers Burdeos, because the keto diet restricts carbs, you're likely eating less fiber—which comes in carbs like fruits, legumes, starchy foods, and grains. “A decrease in fiber intake can lead to diarrhea, among other gut-related problems like changes to the gut microbiome,” says Burdeos, adding that certain carbs are especially beneficial for the gut microbiome, particularly those high in fiber and nutrients like fruits, vegetables, and whole grains.

“These foods promote the growth of good bacteria in the gut. A decrease in carbs has been shown to affect the gut microbiome by decreasing the abundance of good bacteria,” she says. “This in turn may lead to gut-related problems like diarrhea and inflammation in the gut.

Ahead, we share the common reasons for keto diarrhea, along with how to remedy the situation, when to see a doc, and more.

What is keto diarrhea?

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

keto diarrhea signs symptoms
Thana Prasongsin - Getty Images

Often, keto diarrhea is actually steatorrhea, a specific type of diarrhea caused by too much fat in the stool, says Karie Cassell, R.D., 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?

Well, there are several things that can cause keto-induced gastrointestinal distress.

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.

What can you do to help symptoms?

Well, there’s some good news for folks running to the bathroom seemingly every hour. As Tamayo stresses for the most part, keto diarrhea tends to resolve with some time. If it doesn't, however, Tamayo says you might want to look deeper into the ingredients in what you’re eating.

“Avoid things with sugar alcohols and artificial sweeteners,” she says, elaborating that if the diarrhea persists even after you eliminate these products from your routine, you can be a risk for ongoing malabsorption and nutrient deficiencies, “so reducing the amount of fat you eat and introducing more vegetables can be necessary.” Tamayo also suggests drinking more water and electrolytes as “essential in managing these symptoms.”

Last but not least, says Tamayo, adding insoluble fiber, like psyllium, to your diet can be a great way to prevent further diarrhea and keep your gut healthy.

close up of a young latin man hand holding a toilet paper at the bathroom
Angel Gruber - Getty Images

Burdeos riffs on this sentiment adding that to relieve these symptoms don’t follow the severely restrictive forms of the keto diet so that you can eat more fiber in your meals. “There are various versions of the keto diet, ranging in how many carbs you can consume. Some as low as only 20 grams of carb in a day, which is roughly equivalent to one slice of bread or 1 to 2 servings of fruit,” she says. “If following a keto diet is a must for you, I recommend working with a registered dietitian who can support you so that your body meets your nutritional needs, including fiber. Carbs not only offer fiber but an array of vitamins, minerals, as well phytonutrients.”

Like Tamayo, Burdeos also reminds individuals to stay well-hydrated to support optimal overall health. “Diarrhea in particular is a dehydrating symptom,” says Tamayo. You may also want to add probiotic-rich foods such as yogurt, kefir, kimchi, and kombucha to your grocery cart, says Tamayo.

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.

How Common is Keto Diarrhea?

If you’re experiencing keto diarrhea, you’re far from alone. “Keto diarrhea is a common side effect of following the keto diet and it's usually experienced in the beginning phase of starting the diet,” says Burdoes.

“However, not everyone who follows the keto diet experiences diarrhea, and for those who do, the severity and duration of symptoms vary widely.” Burdeos shares that the following groups of people are at greater risk of suffering from keto diarrhea:

● People who have a history of gastrointestinal disorders such as Celiac disease and irritable bowel syndrome.

● People who have a low tolerance to fat-rich foods and/or people who have a low tolerance to consuming a greater amount of dairy, as dairy foods like cream, cheese, and full-fat milk are common staples in the keto diet.

● People who rapidly transition to the keto diet particularly if they go right into following the severely restrictive forms of the keto diet.

Tamayo elaborates that keto diarrhea is often subtle, and not necessarily explosive or acute. “It can happen as soon as you start introducing more fats to your diet and resolve within a few weeks, and this is the most common type,” she says, sharing that some individuals will experience no diarrhea and have ongoing constipation, until they start eating products that are labeled as "keto" and contain artificial sweeteners or sugar alcohols, accompanied by constant diarrhea and pain, gas, and bloating.

toilet flush handle keto diarrhea
Kinga Krzeminska - Getty Images

“Individuals who are used to eating whole grains and lower fat content in their diet will likely experience diarrhea sooner and for longer than others,” says Tamayo. “Those who need to take supplements to keep bowels moving from constipation after switching to the keto diet will also see some diarrhea. Overall, individuals with irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD) can also see some diarrhea as a sign of their bodies having trouble digesting fat.”

In these cases, cautions Tamayo, medical advice is often necessary, as the keto diet might not be appropriate.

Speaking of when to see a doc...

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.

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