Going Keto Can Cause Diarrhea—Here’s How To Quell Those Runs

“Constipation is often the biggest problem with the keto diet due to the lack of fiber, but in fact, artificial sweeteners and sugar alcohols, as well as a very high fat diet, can also cause diarrhea,” says Ginger Hultin, RD, a spokesperson for the Academy of Nutrition and Dietetics and owner of Champagne Nutrition.

What exactly is keto diarrhea?

Keto diarrhea is exactly what it sounds like: diarrhea that happens because of the switch to the keto diet. “It could be anything from noticing looser or more frequent bowel movements to full-on diarrhea, which is generally defined as having three or more loose, liquid bowel movements in a day,” Hultin says.

The (somewhat) good news? Dawn Jackson Blatner, RDN, CSSD, says that keto diarrhea isn’t usually reported to be “explosive diarrhea,” meaning the bowels are ejected more forcefully. Rather, as Hultin noted, keto diarrhea can be just noticing more watery stools than usual and/or having bowel movements more often.

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Blatner adds that anyone who switches to a keto diet can potentially experience keto diarrhea as their body learns how to adapt to more fat than they’re accustomed to and not enough fiber.

That said, what is it about the keto diet that can cause such a crappy situation, and is there anything that can be done about it? Here’s everything you need to know about keto diarrhea.

What is the “whoosh?”

First, let’s clear something up. Keto diarrhea is not to be confused with the “whoosh.” They’re two different things. The “whoosh,” Blatner explains, is when you see a large amount of weight loss seemingly overnight (as in, “whoosh” there goes the weight). This isn’t necessarily a good or a bad thing—it’s just biology. “It’s a water fluctuation more than it is actual true weight/fat loss,” she explains.

How do you know a “whoosh” is coming?

So what exactly causes the “whoosh?” “A water weight fluctuation will happen if you eat more carbs or have more salt than usual. This is because carbs and salt cause your body to hold onto water,” Blatner explains. “But then as you reduce carbs and/or hydrate to balance the excess salt, you release that retained water, so it may actually seem like you lost weight, but it’s just water fluctuation.”

What causes keto diarrhea?

Some people, not all, experience keto diarrhea as an unpleasant side effect when switching to the keto diet. There are a few possible reasons for keto diarrhea, Hultin says:

1. Fat can be hard to digest.

In general, fat takes a bit longer for the body to digest. On a high-fat diet like keto, you’re all of a sudden eating lots more avocado, nuts, seeds, meat, olive oil, and other fats than normal—which can disrupt digestion. “When you switch to this high fat of a diet, it can cause diarrhea,” says Hultin.

2. Artificial sweeteners and sugar alcohols can be rough on the stomach.

Additionally, like Hultin said earlier, people often eat higher amounts of sugar alcohols and other artificial sweeteners while on the keto diet. These sweeteners, while low-carb and generally considered safe, can potentially cause bloating and diarrhea when consumed in excess. So if someone is eating lots of keto-friendly products high in sugar alcohols, they might struggle with keto diarrhea.

3. Keto may disrupt the gut microbiome.

The keto diet can also impact the composition of your gut microbiome, which has implications for digestion, too. “There have been some small studies that have found that after three months on the ketogenic diet, the bacteria in the gut change quite a bit, and that could cause diarrhea in some people,” Hultin says. If your body is not used to eating more fats, this could alter the gut bacteria, causing diarrhea and looser stools from poor digestion. (More research needs to be done before this can be considered a conclusive issue.)

How long does keto diarrhea last?

Thankfully, like keto breath, keto diarrhea is not a permanent issue. “I would expect it to occur around the time that you're changing your diet the most so in the beginning, probably the first one to four weeks until the body is able to adjust,” says Hultin.

“However, if a high-fat diet is not easy for your body to digest or if you do have changes in your gut microbiome, diarrhea could be a long-term side effect,” she says. Blatner adds that if keto diarrhea appears long after you’ve started and adapted to the keto diet, there may be negative changes to the gut microbiome. So seeking help from a dietician to review things like variety, fiber, and fermented foods in your diet could be beneficial.

Are there any remedies for keto diarrhea?

Again, Hultin says that keto diarrhea is usually temporary. But in the meantime, if you’re committed to keto, here are some things you can do to help stave off the worst of the runs:

1. Add more fiber to your diet.

“Soluble fiber is the best thing to help calm diarrhea because it absorbs water,” says Hultin. “These options are limited on a ketogenic diet but you could include: citrus, berries, avocado, broccoli, and chia seeds for example,” says Hultin.

2. Drink more water and electrolytes.

You can lose a lot of fluids if you have diarrhea—which is why the Mayo Clinic recommends consuming lots of liquids (water for hydration, and soups and fruit juice for electrolytes and sodium) to replenish your body.

At what point should I be concerned about this side effect?

However, if you have a stubborn case of keto diarrhea, you should consider seeing your doctor. “If you have diarrhea, especially multiple times per day, for over two to three days and if you're experiencing any symptoms of dehydration—dark colored urine, dry skin, headache, feeling dizzy or light-headed, etc.—then you should see a doctor right away,” says Hultin. You might need more serious interventions to prevent serious dehydration and to rule out other potential causes of the diarrhea.

If keto diarrhea persists, it’s worth rethinking the eating plan, says Hultin. “If the body is reacting to the high fat nature of the diet, that probably can't be changed because there's a certain ratio that must be met,” she says. No one eating plan is right for everyone, and your body might just not be cut out for high amounts of fat.

Blatner also suggests consulting with a dietician to help you make changes to the diet and help reduce the side effects. In particular, she says, changes can include slowly increasing fatty food, decreasing foods containing sugar alcohols, and adding in keto-friendly fruits and veggies for fiber such as citrus, berries, green beans, carrots, and tomatoes to help form more solid bowel movements.

Keto FAQs

How do I know I'm in ketosis?

Ketosis is when your body uses ketones for fuel instead of carbs, Blatner says. And the most accurate way to know if your body is in ketosis is through blood, breath, or urine testing. Blatner says the most common and inexpensive option is by using urine stripes to test. “People particularly test at the beginning as they are getting the hang of the diet and then it becomes less important because they understand what to eat,” she says. “Of course if someone is getting the results they want, testing becomes less important because they are measuring success not by ketones but by feeling good and getting a positive outcome.”

What is keto flu like?

Besides keto diarrhea, keto flu is another side effect of switching to a keto diet. “As your body is learning how to use fat and ketones for fuel rather than the usual carbs and glucose, flu-like symptoms occur,” Blatner explains. “During this adaptation period, the negative side effects and symptoms are likely a type of sugar or carb withdrawal. And just like with a usual flu, the main goal is to hydrate with both water and electrolytes.”

Last Thing To Remember

Lastly, keto diarrhea aside, Blatner reminds us that anytime you’re making drastic changes to your diet, it’s always best to consult with your healthcare providers first. This is especially important, she says, for people with heart conditions, kidney issues, and diabetes because a keto diet can change blood sugar and electrolyte levels. And, she adds, “any extreme diets for kids, pregnant/lactating women, or the elderly is not recommended since extra nutrients are needed at those life stages,” Blatner says.

All that said, keto diarrhea or not, remember that there is a whole world of other healthy eating plans out there to discover that don't typically involve gastric distress. Mediterranean diet, anyone? So if short-term or long-term keto isn’t working for you, try other eating styles to find the best fit for you.