Keto Diet Constipation and Diarrhea: Causes and Remedies

If you’re experiencing bowel irregularities on the keto diet, you’re not alone. Constipation is one of the most common issues but many people report diarrhea too.

Needless to say, these gastrointestinal (GI) issues can cut into your quality of life. They could put a dent in your keto enthusiasm, and into your happiness generally.

They also suggest a dent in your health. If your digestive system isn’t running smoothly, the consequences can sap your immunity and energy, along with your comfort. As Hippocrates said, “all disease begins in the gut”.

Fortunately, constipation and diarrhea on keto tends to be short-lived. Very often it is an issue of poor macros structure or drastic change to diet. And if they persist, there are remedies you may wish to consider before consulting a doctor.

I’ll cover those remedies later, along with potential causes. First, however, let’s put these GI symptoms into the broader context of keto flu.

What Is Keto Flu?

Many people experience headaches, fatigue, weakness, muscle cramps, insomnia and digestive issues in the early stages of keto dieting. Collectively, these symptoms are called keto flu.

Keto flu symptoms mimic flu symptoms, as their name suggests. It’s not like you’re running a fever or bed-ridden, but you might feel tired and weak.

At the core, keto flu is the human body adapting to (and protesting against) dietary change. The biggest change? A sharp reduction in carbohydrates.

On a ketogenic diet, you normally consume less than 10% of your calories from carbohydrates. Keeping carbs low keeps the hormone insulin low, which in turn increases the reliance upon the  release and breakdown of stored body fat for energy. This shift toward greater fat-burning is the central process driving the benefits of the keto diet.

But insulin suppression isn’t the only consequence of carb restriction. There are also consequences to the gut.

Constipation and Diarrhea 101

Constipation and diarrhea aren’t just colloquial terms. They’re medical conditions defined by symptomatology. Let me give a brief description of each.

What Is Constipation?

Constipation means having difficulty emptying the bowels. It’s associated with hardened feces, two or fewer bowel movements per week, and decreased quality of life.

There are many potential causes of constipation, including pharmaceutical drugs, diabetes, celiac disease, hypothyroidism, and various anatomic problems. When other causes have been ruled out, a person is said to have functional constipation.

Laxatives are the first-line treatment for functional constipation. For keto-related constipation, however, you may wish to try the remedies presented later in this article before using a pharmaceutical solution.

What Is Diarrhea?

To have diarrhea is to have three or more loose or watery stools per day. Diarrhea is often caused by an infection (like norovirus), but it can also be caused by problems with gut bacteria, digestive enzyme insufficiencies, or food sensitivities.

Compared to constipation, diarrhea is much less common on keto except in cases where people drastically increase fat intake. In fact, a very-low carb diet has been shown to alleviate the symptoms of IBS-D, or diarrhea predominant irritable bowel syndrome.

Keto Diet Constipation and Diarrhea: Causes

Constipation is a classic keto flu symptom, and some people report diarrhea too. Here’s what might be causing these bowel issues.

#1: Not enough dietary fiber

Dietary fiber is an indigestible carbohydrate. Why indigestible? Because fiber is plant material that isn’t broken down by digestive enzymes. It doesn’t go through normal digestive routes.

But indigestible doesn’t mean nothing digests it. Gut microbes do. And when you shift the fiber supply to these microbes, you shift your digestive health. I’ll cover this more in the next section.

Fiber also adds bulk to stool and promotes bowel motility. In other words, eating fiber helps keep things moving down there. I would be remiss, however, not to mention that there are a subset of people for whom fiber does not improve motility and can actually have a converse response of causing constipation. It’s almost as if the modern study of gut health is relatively new and quite complicated!

On keto, fiber intake can plummet. When you eliminate grains, fruits, and starchy vegetables, you’re eliminating rich sources of dietary fiber. The result is often constipation.

#2: Gut microbiome shifts

Any dietary shift will affect the vast colony of different bacteria, yeast, and viruses living in your gut. Some shifts have good consequences, others bad.  This is an important point—evidence of gut change is not an immediate indicator of harm.

Everyone has a different gut. Depending on the state of your gut, a keto diet may affect your gut microbiome (and your GI symptoms) in different ways.

For instance, restricting carbohydrates appears to be an effective treatment for SIBO, or small intestinal bacterial overgrowth. Around 50% of those suffering with irritable bowel syndrome (IBS) test positive for this condition, and it’s suspected to cause diarrhea.

Essentially, a keto diet “starves” the bad bacteria in the gut, clearing up the diarrhea. But in another person’s gut, starving bacteria may lead to constipation.

Related to this: a keto diet has been found to reduce the diversity of bacteria in the gut. Less diversity is generally considered a negative, but in some of this research, the reduction was in pathogenic strains and the net effect was positive.

#3: Issues digesting fat

Some percentage of people will have trouble digesting large quantities of fat on the keto diet. The problem may be due to the pancreas not producing enough fat-digesting enzymes, like lipase.

Also, certain types of fat—like coconut oil and MCT oil—can have a rapid laxative effect because they tend to remain in circulation for a longer time. The trick with these fats is to start slow, and work your way up one teaspoon at a time.

Additionally, it is generally good to avoid swallowing up your caloric limit with nutrient-lacking calories like liquid fats. This is especially true if fat loss is your goal, but it gets a bit more feasible when you are at your maintenance weight or trying to bulk.

#4: Electrolyte issues

Electrolyte imbalances can cause constipation or diarrhea. For instance:

  • Hypokalemia (low serum potassium) and hypercalcemia (high serum calcium) can cause constipation.
  • Taking too much magnesium—especially poorly absorbed forms like magnesium sulfate—can cause diarrhea.

Potassium may be especially relevant to keto constipation, since keto restricts many potassium-rich foods like bananas and potatoes. There are, however, some great high-potassium options for low-carb dieters such as lean beef, dark leafy green veggies, avocado, etc.

#5: Dehydration

The keto diet has a diuretic effect. Because of this, keto dieters can lose more fluids through urine than they’re taking in.

This is called dehydration, and it’s a potential cause of constipation. Being low on fluids means less fluids are available to loosen stools.

Keto Diet Constipation and Diarrhea: Remedies

The remedies for digestive issues on keto follow directly from the causes listed above. To be clear, serious cases of constipation and diarrhea warrant medical attention. Use your best judgement.

That said, try these tips first for mild to moderate GI issues on keto.

#1: Eat non-starchy vegetables

If you’re constipated on keto, consider eating more keto-friendly vegetables.

Low-carb veggies like kale, spinach, asparagus, and broccoli are some of the best sources of fiber around. Fiber, remember, serves as a bulking agent and helps push waste out of your body.

#2: Restrict fiber

If you’re suffering from diarrhea on keto, consider eating less fiber. This is the opposite from the first recommendation, I know, but there’s clinical evidence suggesting that low-fiber diets can reduce diarrhea and other symptoms of IBS.

Why? Because fiber feeds gut bugs indiscriminately. In the healthy gut, more fiber is usually a good thing. But for those with a deranged gut microbiome—SIBO, for instance—increasing fiber can exacerbate the problem.

#3: Consume probiotics

Probiotics are organisms shown to have health benefits when consumed. These transient voyagers pass through your digestive tract, lower inflammation, improve the integrity of your gut barrier, and disrupt the footholds of pathogens. However, they won’t colonize in the low gut like prebiotics will—so they work only when you take them consistently.

There’s strong evidence for probiotics (especially lactobacilli bacteria) treating infectious diarrhea. But taking probiotics can also help with more chronic GI problems like SIBO, an underrecognized cause of diarrhea.

There are two main options for taking probiotics:

  1. Take probiotic supplements
  2. Eat fermented foods like sauerkraut, kimchi, and yogurt

I recommend dabbling in both—they’ll vary in effectiveness from person-to-person, and have synergies when used together. Check out Chris Kresser’s work on this topic for a deeper dive. It will require some homework and self experimentation.

#4: Hydrate properly

On a keto diet, you lose more fluids through urine. Because of this, you’ll probably need to drink more water to keep your bowels moving regularly.

But when you drink that water, make sure you’re consuming electrolytes like sodium and potassium along with it. (You lose more electrolytes on keto too!). Being low on electrolytes may cause constipation, but the more likely detriment is to your energy.

To prevent this from happening, mix 1-2 sticks of LMNT Recharge into your water bottle each day. We made it specifically for folks like myself, who eat low-carb diets.

#5: Consider magnesium

If you’re having bowel issues on keto, examine your magnesium intake. Magnesium functions as a laxative, and 500-1000 mg of magnesium oxide can be a safe and effective remedy for mild constipation.

If you have diarrhea, consider cutting back on the supplemental magnesium—especially if you’re using magnesium sulfate or magnesium oxide.

#6: Give it time

Your body needs time to adapt to the keto diet. Your pancreas, for instance, may need time to ramp up digestive enzyme production.

Your gut microbiome needs time to adapt too. You’re shifting around nutrients (like fiber) that impact your gut critters. Some will starve, others will thrive.

Give it a week or so, and mind the other remedies on this list. And remember that your gut is a wildly complicated system. You might need to tinker for a while before finding your happy place.