Keto diet constipation and diarrhea: Causes and remedies

From the desk of
Luis Villaseñor
ScienceKeto 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 and many people report diarrhea too.

Needless to say, these gastrointestinal (GI) issues can cut into your quality of life and put a dent in your enthusiasm for keto. They can also obstruct your broader health. When your digestive system isn’t running smoothly, consequences to your immunity, energy, and nutrient deficiencies tend to follow. As Hippocrates said, “all disease begins in the gut.”

Fortunately, constipation and diarrhea related to the ketogenic diet tends to be easily resolved. Very often it is an issue of poor macronutrient intake distribution, or a temporary response to a drastic change in your diet. But if you find these symptoms to be rather persistent, there are a few remedies worth considering.

In this article, I’ll cover a variety of common causes behind gastrointestinal issues — keto-related and otherwise — along with their respective remedies.

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 diet very low in carbs has been shown to alleviate the symptoms of IBS-D, or diarrhea-predominant irritable bowel syndrome.

Causes of Keto Constipation and Diarrhea

Constipation is a classic roadblock for keto newcomers, and some people report diarrhea too. Here are the five most likely suspects.

#1: Not enough dietary fiber

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. Why?

Dietary fiber is an indigestible carbohydrate. It’s plant material which cannot be broken down by digestive enzymes. It passes through digestive routes mostly in-tact, adding bulk to stool and promoting 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 the opposite effect (constipation). The modern study of gut health is relatively new, and pretty complicated!

#2: Gut microbiome shifts

I mentioned that fiber is “indigestible.” This is mostly true but slightly misleading. You see, gut microbes do feed on fiber. And when you deny healthy gut bacteria their daily meal, you shift your digestive health.

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 change in your gut is not always an indicator of harm to your gut. Even when the symptoms are less than pleasant.

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.

Relatedly, 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. Prioritizing protein first and foremost can help.

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 is to start slow. Don’t start shoveling MCT oil like a snow-sealed driveaway — work your way up one teaspoon at a time.

#4: Electrolyte issues

Electrolyte imbalances can cause constipation or diarrhea.

For instance, hypokalemia (low serum potassium) and hypercalcemia (high serum calcium) can cause constipation. 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, and avocado.

Interestingly, taking too much magnesium — especially poorly absorbed forms like magnesium oxide and magnesium sulfate — can both cause diarrhea and help alleviate constipation. Balance is key.

#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.

Remedies for Keto Constipation and Diarrhea

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 judgment, and seek medical help before things get out of hand.

That said, for mild to moderate GI issues on keto, it may be worth trying these tips first.

#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: Potentially 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 ways you can get probiotics: supplements, and 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 experimentation.

#4: Hydrate properly

On a ketogenic 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, try mixing LMNT into your water bottle each day.

#5: Consider magnesium

If you’re having bowel issues on keto, examine your magnesium intake. Magnesium functions as a laxative, and 500-1,000 mg of magnesium oxide can be used as an 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 (consider switching to magnesium malate).

#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.

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