You’ve heard about all of the benefits of going low-carb, but for transparency, you may want to know about keto bloating and gas. The good news is, it’s temporary, and not everyone experiences it.
You know I’m a big fan of self-experimentation, but here’s the rub. Whenever you try something new— be it a new diet, sleep hack, exercise program, whatever—you hope the results will be favorable. Unfortunately, though, you can’t guarantee a good result. Or at least, you can’t guarantee a good result immediately. Sometimes there’s an adjustment period before you get the outcome you want.
That’s certainly true with a keto diet. For most people, especially folks who aren’t already eating Primally, going keto means significant dietary changes. All of a sudden, they’re eating many more healthy fats, animal products, and vegetables; few or no grains or legumes; and limited root vegetables and fruits.
Any time you change up your diet, your gut can take a while to adapt. It shouldn’t surprise us, then, when we hear reports of digestive irregularities like bloating and constipation when people switch to keto. In my experience, these are usually mild and short-lived. Of course, since keto is the diet that conventional wisdom loves to hate, critics have jumped on this. They’ll take any opportunity to besmirch ketogenic diets and whip up fear over small or non-existent issues. (Remember the blessedly brief frenzy over keto crotch? That was a weird time.)
The question at hand today is whether so-called “keto bloat” is a real, widespread side effect of keto diets. Let’s dive in.
What Is “Bloat” Anyway?
“Bloating” is something of a catch-all phrase used for any abdominal discomfort or swelling. Most commonly (and most correctly), bloat refers to abdominal distension, or “pooching” of the belly, often accompanied by gassiness.1 Some people also use the term to describe the heavy, overfull feeling you might get after eating. Still others conflate bloating with constipation.
Since bloat means different things to different people, right off the bat it becomes difficult to pin down whether keto regularly causes bloating. For the purposes of this post, I’ll focus separately on bloating, meaning abdominal distension and gassiness, and constipation. Although bloating and constipation are separate afflictions, they often occur together.
Is Keto Bloating a Big Problem?
According to Big Fiber, all of us low-carb enthusiasts are ticking time bombs. Due to the “lack of fiber” in keto diets, we’re walking around with colons on the verge of blowing up at any second.
Are millions of keto dieters suffering from bloating and constipation? I can find no evidence of this.
Is fiber necessary to prevent bloating and constipation? It’s complicated, but probably not. I’ll explain below.
Does the ketogenic diet necessarily exclude fiber? Not at all.
Are nutritional (non-therapeutic) ketogenic diets low in fiber in practice? No.
As I alluded to up top, I suspect that most of the issues with bloating and constipation occur during the adaptation phase, which to me means anywhere from two weeks to two months after starting a keto diet. This is based on my personal observations and from listening to folks in the Keto Reset community. However, let’s see if the scientific literature has any insights to offer.
What Is the Evidence That Keto Causes Bloating?
There’s almost none. I’ve only seen bloating mentioned in the ketogenic diet literature in studies that use medium-chain triglyceride (MCT) oil to increase the production of ketone bodies.2 Gastrointestinal issues including bloating, cramps, and diarrhea are common side effects of overdoing the MCT oil, as I unfortunately know from personal experience.
This seems like a cautionary tale about going too heavy on the MCTs rather than a condemnation of keto diets per se.
Keto and Constipation
Constipation does seem to be a relatively common occurrence. One review found that among epileptic children, constipation was the most common adverse effect of ketogenic diet therapy, occurring in 13% of the kids.3 Remember, though, that the therapeutic keto diet, with its extreme carbohydrate and protein restriction, barely resembles the keto diet most of you are familiar with. And in studies of less extreme, more realistic versions of the diet, such as modified Atkins (which allows more protein) or a version with “heavy focus” on vegetables, nuts, and seeds,4constipation happens at a much lower rate. For example, in one study on the modified Atkins diet, just 2 of 26 subjects complained of constipation.5
Thus, it seems probable that keto diets are not inherently causing constipation unless they involve rather extreme restriction. Relevant here is another study of children with epilepsy placed on an olive oil-based ketogenic diet.6 About 25% of the subjects experienced constipation, BUT those who experienced constipation were actually less likely to be in ketosis. Constipation improved as ketone readings went up and epilepsy symptoms subsided.
It’s unclear how widespread this problem is in the keto diet world at large, particularly among people who eat a “well-formulated ketogenic diet,” meaning one that includes a diverse array of plant foods alongside animal products and healthy fats. I do hear from some people who experience reluctant bowels—again, especially during the transition phase. What might be causing it?
Why Am I Bloated on Keto?
Okay, say you are dealing with constipation or bloating on a keto diet. What could be going on?
Too Little (Or Too Much!) Little Fiber
Let’s get this out of the way first: keto is not inherently a low- or no-fiber diet, despite what you might have heard. Keto folks can get plenty of fiber from enjoying a variety of vegetables, nuts, and seeds.
In any case, the relationship between fiber and constipation is decidedly mixed. Sometimes higher fiber intake does seem to help. Psyllium husk and flaxseed have both been shown to improve constipation.78 Galactooligosaccharides, a class of prebiotic fiber, improve idiopathic constipation.9 And inulin, another prebiotic fiber, improves bowel function and stool consistency in patients with constipation.10
But there’s also evidence that more fiber can make the problem worse. In one 2012 study, patients with idiopathic constipation—constipation without apparent physiological or physical causes—had to remove fiber entirely to get pooping again.11 Those who kept eating a bit or a lot of it continued to have trouble evacuating. The more fiber they ate, the worse their constipation (and bloating) remained. Another review found mixed evidence; some people get less bloating and constipation with more fiber, others get less bloating and constipation with less fiber.12
There’s no one-size-fits-all with fiber, especially since there are many different types of fiber. It does seem possible that constipation could occur if you change the sources of your fiber when you go keto, even if the overall levels don’t change dramatically. After all, we know the gut microbiome starts to change rapidly within a day or two of changing your diet.13 If you need a little help on the pot, try adding a serving of psyllium to a smoothie (start with 1 teaspoon of ground husks), or mix it in a small amount of water and shoot it—effective but not all that pleasant. If the problem gets worse, try the opposite. Limit your fibrous veggies for a day or two and see if that helps, then slowly reintroduce them.
Not Enough Food
Constipation is often a consequence of low energy status. Everything that happens in the body requires energy, and if energy levels are low or energy availability is poor, basic functions will suffer. Bowel movements are no exception. The muscles and other tissues responsible for moving things along your digestive tract use energy. If you aren’t providing adequate amounts of energy, you’re depriving your tissues of the ATP they need to work best and sending your body a signal of scarcity which will only depress energy expenditure even more.
Low-carb diets in general, and keto diets in particular, are very good at causing inadvertent calorie reduction. It’s great for fat loss, but some people go overboard with their caloric deficit. I’m talking 800-1000 calories a day on top of CrossFit. That’s a recipe for disaster.
Water and Mineral Loss
When you go keto for the first time, you shed tons of water. For every gram of glycogen you lose, you drop 3-4 grams of water. You also lose sodium and potassium with the water, and you need extra magnesium to regulate your sodium and potassium levels.
The water content of stool is what gives it that smooth texture we all desire. If you’re dehydrated, even mildly, you’ll have less water available for your bowel movements and be more likely to suffer from constipation.14
Drink a big glass of salty water with lemon juice in the morning and sip on salty broth throughout the day. Zucchini is a great source of potassium, as is avocado.
Also, if you’re going to eat more fiber, you need to increase water intake for it to work.
Too Many Keto Sugar Substitutes
I get it. There are some interesting candies out there that cater to the keto set and use various sugar alcohols—non-alcoholic, low-or-no-calorie sweeteners—artificial sweeteners, and fibers to recreate popular treats. It’s fun to eat an entire chocolate bar that tastes pretty close to the real thing and get just a few net carbs. But that’s a lot of fermentable substrate your gut bugs are more than happy to turn to gas. The sugar alcohols ending in -ol like erythritol, maltitol, and xylitol are especially likely to cause gas and bloating.
The myth is that keto people are eating salami and cream cheese for every meal. The reality is that many people go Primal or keto and find they’re eating way more vegetables than they ever have before. These are great developments, usually, but if you’re intolerant of FODMAP fibers, you may worsen the bloating.
FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols—the carbohydrates in plants that our gut bacteria usually mop up. Most people have gut biomes that can handle FODMAPs; indeed, most people derive beneficial short-chain fatty acids from their fermentation. However, some people’s gut biomes produce too much fermentation when they encounter FODMAPs. Fermentation begets hydrogen gas, which gathers in the gut and causes great distress. Common complaints of FODMAP intolerance are bloating, stomach pain, and visits to the toilet that are either unproductive or way too productive—all of which fall into the bloating category.15
What Can You Do?
Eat enough protein. Most people can get away with eating 15-25% of their calories from protein and still stay in ketosis. Most people can eat even more protein and still get most of the benefits of fat-adaptation. The keto studies which had the lowest rates of constipation were far more tolerant of higher protein intakes.
Eat FODMAPs unless you’re intolerant. Most people can eat FODMAPs. In most people, FODMAPs improve gut health and reduce constipation and bloating. But if your gut blows up after a few bites of broccoli or asparagus, consult the FODMAPs list and try a quick FODMAP elimination diet.
Check your consumption of common food culprits. This includes sugar alcohols and MCT oil, plus one I haven’t mentioned yet: dairy. While I dislike the stereotype of keto folks eating nothing but cheese and heavy whipping cream, it’s true that a lot of people up their dairy intake once they give themselves permission to fully enjoy healthy fats. If you’re spending more time than usual in the dairy aisle, try taking a break from dairy and see if your problems resolve.
Experiment with fiber. Fiber clearly has a relationship to bloating and constipation. You just have to figure out what that looks like in your diet.
If you’re bloated and constipated on a high-plant keto diet, eat fewer plants.
If you’re bloated and constipated on a low-plant keto diet, try eating more plants.
If neither of those helps, try a very low or zero-plant carniflex diet.
Try adding magnesium for constipation. Electrolyte supplementation is always important, especially when starting a keto diet. Magnesium in particular can help move things along if you’re having trouble going. Try a small serving of magnesium—the oxide and citrate forms tend to have the greatest laxative effect—and increase the dose until it starts to work.
Finally, make sure you’re truly constipated. Your stool volume and frequency of toilet visits will decline on a normal ketogenic diet because there’s less “waste.” Make sure you’re not misinterpreting that as constipation or bloating. If there’s less poop, there’s less poop. If there’s more poop but it’s just not coming, and you have to go but can’t, that’s when you have an issue.
So, to sum up, “keto bloat” may occur for some people, but the scope of the problem is highly exaggerated from what I can tell. Constipation is somewhat common, particularly on the most restrictive clinical keto diets, but you can help yourself out by:
Eating fiber from vegetables, nuts, and seeds
Being less restrictive with protein
Making sure you’re drinking enough water
Eating enough calories
Getting sufficient electrolytes through food and supplements
What’s been your experience with bloating and constipation? How have you handled it?
Keto Bloating FAQ
Do keto diets cause bloating?
Sometimes, but it’s not unique to keto. Any dietary shift can cause (hopefully temporary) gastrointestinal issues like gas, abdominal distension, or constipation, especially if you’re eating a lot of new foods, you’re getting a lot more or a lot less fiber, or you’re consuming different types of fiber.
How can I relieve bloating fast?
For constipation, make sure you’re drinking enough water, then consider supplementing with some magnesium oxide or citrate, psyllium husks, or inulin. For gas and distension, try walking or gentle yoga poses like child’s pose. For longer-term relief, experiment to see if specific foods are giving you trouble.
What are some keto foods that help with bloating?
High-fiber vegetables, nuts, and seeds can help with constipation. Keto-friendly favorites like avocado, artichokes, broccoli, Brussels sprouts, almonds, and chia seeds all pack good amounts of fiber. Excess fiber can cause gas, though, and high-FODMAP vegetables worsen bloating for some people. Everybody responds differently. A personalized approach is needed.
Can too much fiber cause constipation and bloating?
Most people believe that constipation is the result of consuming too little fiber. However, research also shows that too MUCH fiber can also cause constipation. Some people, including people with IBS, have better bowel movements and less bloating when they limit their fiber intake.
Is bloating one of the side effects of erythritol and other keto sweeteners?
Yes. For some people, sugar substitutes and artificial sweeteners are associated with gastrointestinal issues such as bloating, cramping, constipation, or diarrhea. Sugar alcohols may be especially prone to causing problems. These include erythritol, xylitol, maltitol, sorbitol, mannitol, and isomalt. If you struggle with bloating, try temporarily eliminating keto sweeteners.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.