Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...Tell Me More
According to the “good scientists” of the Kellogg company food lab, an unprecedented number of young people are walking around with bloated guts and colons packed to the brim with impacted fecal matter, and it’s all because they’ve embraced ketogenic diets and “forsaken” fiber.
If this sounds like nonsense, that’s because it is.
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. I’ll explain later. But probably not.
Does the ketogenic diet necessarily exclude fiber? Not at all.
Are ketogenic diets as commonly practiced low in fiber? No.
There are two things that people refer to as bloat: constipation and abdominal distension.
Constipation has different components. It’s being unable to make a satisfying bowel movement. It’s also feeling like you have to poop but are unable to. It’s being able to poop only a little bit. It’s struggling on the toilet bowl. Mostly, it’s being unhappy with your performance on the toilet.
Abdominal distension also can be different things. It might be trapped gas. It might be feeling “heavy” or “full.” It might mean your pants don’t fit after eating.
So, “bloating” can be any or all of these. You can pass hard small stools and feel like you’re bloated. You can poop just fine but have a lot of gas and feel like you’re bloated. You can spend hours on the toilet with not much to show for your effort and be bloated. So “Keto bloat” is difficult to pin down. That makes it easy to make claims and hard to disprove.
Let’s see how frequent bloating and constipation occurs in the ketogenic diet literature.
In a study of children with epilepsy placed on an olive oil-based ketogenic diet, about 25% of the subjects experienced constipation. So, was ketosis slowing them down? Not exactly. Those who experienced constipation were actually less likely to be in ketosis. Constipation went up as ketone readings went down, and epilepsy symptoms returned. Constipation improved as ketone readings went up and epilepsy symptoms subsided.
In adults with epilepsy on a ketogenic diet, constipation occurred in just 9% of patients. The authors note that this rate is lower than some other ketogenic studies and attribute the difference to “the heavy focus on importance of fiber from nutrient dense (fiber rich) vegetables, nuts, and seeds.” Note that they weren’t getting fiber from pills and powders. They were eating nutrient-dense foods that just so happened to contain fiber.
Another ten-year study compared the classical ketogenic diet, MCT oil-based ketogenic diet, and modified Atkins keto diet. They were all equally effective at reducing epilepsy symptoms in children, but the occurrence of constipation varied greatly. It was most common in the classic keto diet and medium chain triglyceride-based diet, both of which restrict protein. In the modified Atkins diet, which does not restrict protein, constipation was much rarer. Another study on the modified Atkins diet had similar results, with just 2 of 26 subjects reporting constipation.
Constipation does seem to be a common occurrence. However, the majority of keto diet studies are in epileptic populations following very strict clinical Keto diets. The extreme nature of these therapeutic ketogenic diets—extreme protein (7% of calories) and carbohydrate restriction—makes them an imperfect representation of how most people are eating Keto. And in studies of less-extreme, more realistic versions of the diet, such as modified Atkins (which allows more protein) or the version with “heavy focus” on vegetables, nuts, and seeds, constipation occurs at a much lower rate.
The only instance of something approximating bloating in the ketogenic diet literature occurred in studies using medium chain triglyceride-based diets. These are ones that use huge amounts of MCT oil to increase production of ketone bodies. It works great for curbing epilepsy symptoms, but it can also cause cramping, diarrhea, and abdominal pain. That’s not bloating per se. It’s literally the closest I could find.
Okay, say you are dealing with constipation or bloating on a keto diet. What could be going on?
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. Great for fat loss, but some people take it overboard and go too far. I’m talking 800-1000 calories a day on top of CrossFit. That’s a recipe for disaster.
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.
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.
The relationship between fiber and constipation is mixed. Some interventions do seem to help. Psyllium husk and flaxseed have both been shown to improve constipation. Galactooligosaccharides, a class of prebiotic fiber, improve idiopathic constipation. And inulin, another prebiotic fiber, improves bowel function and stool consistency in patients with constipation.
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. 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.
Personally, my toilet performance is stellar with or without a constant intake of voluminous levels of plant matter. Most days I eat a good amount—Big Ass Salads, broccoli, sautéed greens, berries—but on the days I don’t, I don’t notice any difference. I’m suspicious of the widespread calls for bowel-rending levels of fiber as the universal panacea for all things toilet, and I’m also suspicious of the people who claim fiber is unnecessary or even harmful.
Fiber helps some people and hampers others. There’s no one-size-fits-all with fiber, especially since there are many different types of fiber.
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 versions of sugar—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.
If you want the opposite problem, you can always turn to Haribo sugar-free gummy bears.
FODMAPs 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. But 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 the FODMAP intolerant 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.
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.
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.
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.
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.
We all have to find our sweet spot.
So, to sum up, “keto bloat” is mostly a myth. There’s a glimmer of truth there, but it’s highly exaggerated. Constipation is common on the most restrictive clinical keto diets, while eating fiber from whole plant foods, being less restrictive with protein, and making sure you’re drinking enough water and eating enough calories and electrolytes seems to avoid the worst of it.
What’s been your experience with bloating and constipation? How have you handled it?
Ho KS, Tan CY, Mohd daud MA, Seow-choen F. Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms. World J Gastroenterol. 2012;18(33):4593-6.
Müller-lissner SA, Kamm MA, Scarpignato C, Wald A. Myths and misconceptions about chronic constipation. Am J Gastroenterol. 2005;100(1):232-42.
Guzel O, Uysal U, Arslan N. Efficacy and tolerability of olive oil-based ketogenic diet in children with drug-resistant epilepsy: A single center experience from Turkey. Eur J Paediatr Neurol. 2019;23(1):143-151.
Roehl K, Falco-walter J, Ouyang B, Balabanov A. Modified ketogenic diets in adults with refractory epilepsy: Efficacious improvements in seizure frequency, seizure severity, and quality of life. Epilepsy Behav. 2019;
Liu YM. Medium-chain triglyceride (MCT) ketogenic therapy. Epilepsia. 2008;49 Suppl 8:33-6.
Arnaud MJ. Mild dehydration: a risk factor of constipation?. Eur J Clin Nutr. 2003;57 Suppl 2:S88-95.
Noureddin S, Mohsen J, Payman A. Effects of psyllium vs. placebo on constipation, weight, glycemia, and lipids: A randomized trial in patients with type 2 diabetes and chronic constipation. Complement Ther Med. 2018;40:1-7.