Some people experience constipation on low-carbohydrate and ketogenic diets and worry that it is due to a lack of fiber. If you are one of them, take heart! Fiber is not the answer! What is? Read on . . .
The authors of Keto Clarity, Jimmy Moore and Dr. Eric Westman, acknowledge that some people develop constipation on ketogenic diets, and offer some recommendations about how to address the problem, including drinking enough water, increasing non-starchy, fibrous vegetable intake, and using sugar-free candy containing sugar alcohols as a mild laxative. I do agree that these approaches may certainly be helpful for some. However, if you have tried these suggestions and they haven't worked for you, or if you have trouble with constipation no matter what kind of diet you eat, I would like to offer some insights that you may find useful. Most people believe that constipation is caused by a lack of fiber in the diet, but this is actually not so. My opinion, based on clinical and personal experience, common sense, and lots of reading of the scientific literature, is this:
Constipation is usually caused by something you ARE eating, not by something you’re NOT eating.
Lack of fiber does not cause constipation. In fact, fiber can actually CAUSE constipation! Take a look at this 2012 study that proves it: "Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms."
“This study has confirmed that the previous strongly-held belief that the application of dietary fiber to help constipation is but a myth. Our study shows a very strong correlation between improving constipation and its associated symptoms after stopping dietary fiber intake.”
Plenty of people and animals have eaten mostly-meat/all-meat diets and do not suffer from constipation, and plenty of people eat high-fiber diets and even vegan diets and suffer from constipation.
If you are lucky enough not to have constipation on a regular diet and then develop constipation on a ketogenic diet, it is almost certainly not because you are eating more meat and less fiber. Ask any gastroenterologist or physiologist and they will tell you this: Meat and fat are easily and completely digestible!! Fiber, on the other hand, is partially or wholly INdigestible by definition (for more information about the nature of fiber see my article “Pulp Fiction”). Unless you have certain uncommon digestive diseases, such as pancreatic insufficiency, or have had certain surgical procedures that interfere with normal digestion, such as gastric bypass surgery, you simply will not find undigested meat or fat exiting your body. . . Whereas everyone is guaranteed to find plenty of undigested vegetable matter, right?
If you experience constipation on a ketogenic diet, it is not because you are eating less fiber; it is most likely because you have started eating something that you were not eating before (or a larger amount of something you didn’t eat much of before) that is hard for you to digest. In order to eat a ketogenic diet—a high-fat, limited protein, ultra-low-carb diet—most people find themselves turning to high amounts of foods that are notoriously difficult to digest, including nuts, low-starch vegetables such as crucifers, and full-fat dairy products. These foods just so happen to be three of the top five causes of chronic constipation regardless of what kind of diet you choose to eat.
One more consideration—sometimes food sensitivities can cause constipation in certain individuals, so if you have eliminated the five most common constipation culprits and still have difficulty, consider that you may be uniquely sensitive to something that most people have no trouble digesting. Examples that come to mind are eggs and beef. Eggs are among the top nine common food sensitivity culprits, and beef can cause trouble for some people who don’t do well with dairy products because of a cross-reactivity related to cow proteins. These are unusual experiences, but worth mentioning.
Many plant foods—especially stems, seeds, nuts, grains, and legumes—are challenging to digest (which is why herbivores—animals who eat an all-plant diet—have special digestive strategies such as chewing all day long and carrying around extra stomachs). Fruit, however, is easy to digest—so easy, in fact, that eating too much of it can cause the opposite of constipation! [Read my fruits page to learn the fascinating reasons why fruits digest so rapidly and how sugar alcohols can be used as laxatives.] Ketogenic diets tend to contain little if any fruit, because most fruit is too high in carbohydrate. However, there are some low-carbohydrate fruits that we think of as vegetables—foods like cucumbers, tomatoes, squashes, avocado, okra, and olives—that you can enjoy on your low-carbohydrate diet (so long as you count their carbohydrate content and don’t overdo it) that will aid speedy digestion. Just remember: any “vegetable” that contains seeds is actually a fruit in disguise and should be easy to digest if ripe.
So if you experience constipation on your ketogenic diet, don’t blame the meat, fat, or lack of fiber. Take a look at what you’re eating and see if you can identify your culprit. With a little tweaking, you should be happily on your way!
If you'd like to learn more about ketogenic diets including how to start, tips for success, and additional resources, check out my post "Ketogenic Diets 101."