If you are new to the keto diet you probably have some concerns about whether or not the recommended foods will provide you with enough fiber. The truth of the matter is, lowering, and almost eliminating fiber in your diet will have huge benefits.

In this article we will examine the myths surrounding the so called benefits of fiber, and highlight some of the research that debunk these myths. 

Credit for most of the information provided in this post, and the associated research links goes to Dr. Ken Berry. Whether you are looking to start keto, or have been following keto for years, Dr. Berry is a fantastic resource to help you cut through the BS.

Table of Contents

What is Fiber?

Fiber is simply plant material that we cannot digest. It is categorized in two ways, soluble fiber, which dissolves in water, and  insoluble fiber, which does not.

Google the word fiber, and you will be inundated with dozens of unsubstantiated benefits of fiber including; lowers blood pressure, blood sugar and cholesterol, improves bowel movements, prevents colon cancer, promotes weight loss, and helps detoxify the body. 

Despite all of the hype, it might surprise you to know that there is little to no legitimate scientific support for these claims about fiber.

We Didn't Need Fiber Before - So What Changed?

As a biologist, I have studied the diets and digestive physiology of both animals and humans. 

Evolutionarily and biologically, humans are categorized as facultative carnivores. A facultative carnivore is primarily a meat-eater that is unable to thrive without animal based foods. 

What makes a carnivore facultative is its ability to subsist, for a time, on some types of plant material, however this is a survival mechanism, and not optimal long term.

Why not? We simply aren’t designed to digest plant cellulose, and therefore cannot secure adequate nutrition from an all plant diet, without supplementation.

Mammalian herbivores are equipped with specialized stomachs, sometimes multiple, and long complex digestive tracts in order to facilitate microbial fermentation. 

Human’s on the other hand have a single acid based stomach, and relatively short and simple intestines or guts, just like other carnivores.

The diets of humans during millions of years of evolution consisted of predominately meat, and a variety of tart fruits, nuts and seeds when seasonally available.

Our physiology hasn’t changed so why the sudden push to consume more plant material and fiber?

Where it all Went Wrong

Many people attribute the push towards high fiber diets to Dr. Denis Parsons Burkitt, also known as The Fiber Man

In his 1979 book Don’t Forget Fiber In Your Diet, Dr. Burkitt concluded that many western diseases, which were rare in Africa, were the result of diet and lifestyle, and associated particularly with low fiber intake.

While he did identify other dietary differences between Africans and Westerners, such as the near absence of processed foods, and the higher consumption of animal fats, he mistakenly credited higher fiber intake for the health benefits.

He also had an alternative theory that the use of the natural squatting position during defecation protected natives of Africa and Asia from gastrointestinal diseases. It’s a good thing this was a secondary theory, otherwise he may have ended up with a much different nickname.

Dr. Burkitt was a very respected surgeon and had made other significant contributions to medical science, including the identification, distribution and etiology of what is now known as Burkitt’s Lymphoma, so his theories surrounding fiber were essentially accepted as gospel. 

It is important to note that the theories he presented in his book had not been tested, and were essentially an educated guess or hunch based on how he interpreted his observations. 

Myth #1 - Fiber Supports Healthy Weight Loss

While there is evidence that fiber can contribute to weight loss, the manner in which it works is not exactly healthy.

The approach is simple. We can’t digest fiber so it sits in our digestive tract for long periods of time making us feel full. Because we feel full, we eat less, and by eating less we ultimately lose weight. 

Seems like a logical approach, but here’s the problem. Fiber provides no nutritional value and therefore consuming large amounts results in less room for more nutritious foods. 

Holding a bulk of fiber in our systems also interferes with the proper digestion of other foods consumed along with the fiber, and many recommended high fiber foods, such as wheat and other grains, actually trigger hunger and impede in the absorption of nutrients.

Want a better way to curb hunger and lose weight? Eat more fat.

Myth #2 - Fiber Helps Relieve Constipation

Adding fiber when constipated further slows digestion, and in the case of soluble fiber, absorbs moisture, making things worse. It is basically the equivalent of adding toilette paper to help unblock a toilette.

Eating less fiber, and staying well hydrated are the best ways to prevent constipation, and consuming a few tablespoons of apple cider vinegar diluted in water is a great way to get things moving. 

Research Link – Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms.

Myth #3 - Our Healthy Bacteria Need Lots of Fiber

While it is true that our gut bacteria can breakdown small amounts of fiber, this doesn’t mean that consuming fiber provides any real benefit. 

Remember, there is no nutrition in fiber so breaking it down is of little benefit to us or to the bacteria. What is actually produced from breaking it down is a small amount of short chain fatty acids, which are better sourced elsewhere, and loads of gas.

That’s right. The bloating, cramping and gas you have been experiencing while loading up on fiber is due to the methane and carbon dioxide released when your gut bacteria attempts to breakdown fiber.

One of the most immediate and profound changes I noticed when going keto was no more bloating or gas. 

Myth #4 - Fiber Lowers Blood Sugar & Cholesterol

Similar to the weight loss myth, there is some support for fiber in lowering blood sugar and cholesterol, but increasing fiber intake is not the best way to address these issues.

If 10-15% of your diet is fiber, you are technically eating less actual food and therefore your blood sugar and cholesterol may go down, however there are far better ways to accomplish this.

First off, consuming less carbohydrates and sugar to begin with will have a far greater influence on lowing blood sugar and insulin, and second of all, when it comes to heart disease, cholesterol is not the problem, inflammation is.

Myth #5 - Fiber Helps Prevent Colon Cancer

Proponents of high fiber diets will almost always make the claim that large amounts of fiber are beneficial for ‘scrubbing’ the interior walls of the colon, thus improving the health of the colon and preventing colon cancer.

As mentioned above, maintaining a bulk of undigestible fiber in our guts actually interferes with the proper digestion of food, and the absorption of nutrients. 

It is also unnecessary to run a Brillo pad of fiber through your colon, and doing so can actually damage the walls of the colon.

The next time someone poses the argument that high fiber diets help prevent colon cancer, present them with the following studies.

The first study, linked here, is a meta analysis of five randomly controlled trials in humans, which is important to note. The reviewers hypothesized that eating more fiber would decrease the risk of colon cancer.

Their conclusion however was – There is currently no evidence from randomly controlled trials to suggest that increased dietary fiber will reduce the incidence or recurrence of adenomatous polyps (the precursors of colon cancer) within a two to four year period.

The second study, linked here, is a meta analysis of 13 cohort studies from pooled data involving 725,628 men and women over a 6-20 year period. 

The conclusions of this study – In this large pooled analysis, dietary fiber intake was inversely associated with risk of colorectal cancer in age-adjusted analysis. However, after accounting for other dietary risk factors, high dietary fiber intake was not associated with a reduced risk of colorectal cancer.

Myth #6 Fiber Supports Detoxification

Google ‘how to detox your body’ and you will be hit with a barrage of people promoting products that they claim will help remove toxins from your body, most of which are just overpriced and absolutely unnecessary fiber supplements.

The best way to detoxify your body is to fast. Period.


Prior to the agricultural revolution, humans thrived by consuming predominately fatty meats, and little to no fiber, and our physiology has not changed.

Most of the past literature promoting the consumption of high fiber foods has been debunked by more current  and robust research, and we are learning more and more each day just how far we have gone off course in our diets due to the influence of the food industry.

Have you tried reducing you fiber intake? How did you feel? Please consider sharing your experience by commenting below to help support others navigating a healthy keto lifestyle.

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