Fiber Myths and Truths: Do We Really Need Fiber?

By Thomas Wrona Published on

Table of Contents

The myth that fiber is universally healthy and necessary is one of the most persistent in mainstream nutrition.

A more accurate understanding of fiber can be seen in the instance when Parks and Rec’s Ron Swanson was once served a plate of vegetables in place of his normal meaty meal.

“Excuse me,” he told the waiter. “There’s been a mistake. You’ve accidentally given me the food that my food eats.”

While this statement was meant to be funny — and it is— it also conveys a biological truth. Ron Swanson’s food of choice–beef–digests those veggies way better than he could ever hope to. Ruminant animals like cows are able to ferment all that plant fiber into fatty acids (in essence, they’re eating keto). 

But we humans run off of a different digestive “operating system.” Our bodies are designed to chew, ingest, and process a diet primarily composed of animal products–meats, organs, marrow etc.

In fact, recent research suggests that humans evolved as hyper-carnivorous apex predators for nearly 2 million years!  

This view that we humans don’t have the physiological system to healthfully digest lots of fibrous plant foods runs contrary to everything that common sense tells us. 

But as Albert Einstein once said, “Common sense is nothing more than a deposit of prejudices laid down in the mind before you reach eighteen.” When it comes to fiber this could not be truer. 

The Fiber Myth

For decades we’ve been told the fiber myth that our bodies can’t run right without plants. Plants, the thinking goes, contain fiber. And fiber is a natural pipe cleaner that prevents colon problems, constipation, high cholesterol, heart attacks, and more.

The Institute of Medicine recommends daily fiber intake of  38 grams for men,  and 25 grams of fiber a day for women.

But is fiber actually good us? Do we really need it? Not really. 

Newer, more objective research is showing that dietary fiber is often unnecessary. And it might even be harmful.  

What is fiber? 

According to the Institute of Medicine, dietary fiber is a non-digestible carbohydrate that can come from either natural or synthetic sources. Common types of dietary fiber include:

  • cellulose
  • psyllium husk, 
  • chitin, 
  • fructooligosaccharides, 
  • dextrin.

Fiber is commonly found in fruits and vegetables.

Fiber: grains and vegetables

Image from helpguide.org

Fiber is placed into one of two categories depending on how your body processes it:

  • soluble
  • insoluble 

Insoluble fiber

Fiber is by definition mostly indigestible. Insoluble fiber is completely indigestible, meaning it passes through your entire digestive tract untouched.  According to conventional wisdom, insoluble fiber is good for us because it speeds digestion up.

Insoluble fiber’s physical properties tell a different story, however. It doesn’t dissolve in water or stomach acid. It’s abrasive to the large intestine, and pretty much incompatible with our entire digestive tract.

Soluble fiber

Soluble fiber distinguishes itself from insoluble fiber by being slightly digestible. 

According to conventional wisdom, this type of fiber slows down digestion by absorbing water and keeping the entire GI tract well-hydrated. Soluble fiber gives the intestines a gel-like coating that some experts believe is beneficial.

But there’s a problem — bacteria thrive in this gel coating, too. New research has shown that soluble fiber can make it easier for harmful bacteria to proliferate, potentially leading to conditions like small intestine bacterial overgrowth (SIBO).

Do you need fiber?

As it turns out, humans do not need fiber to survive or thrive. 

Then where did the fiber myth come from?

Turns out, its origins were more of a supply chain solution than a scientific breakthrough. In the late 1800s, grain processors learned how to efficiently separate the bran from the grain, creating ultra-fine, ultra-refined products in the process.

Fiber-free grains and flours quickly became popular throughout the West. People loved their smooth, chewy mouthfeel. 

Sooner or later, though, epidemiologists began to notice that countries with higher refined wheat consumption tended to be sicker. On the other hand, countries or areas that didn’t have access to these new grains remained relatively free from modern diseases.

People assumed that the newly missing fiber was responsible for this difference. And grain processors were happy to make some extra money off their waste products by remarketing husks as fiber supplements. 

In other words, these early epidemiologists mistook correlation with causation and drew the wrong conclusion. A lack of fiber wasn’t the factor making modern diets harmful at all! 

The real culprit was a lack of fat-soluble vitamins, as Dr. Weston A. Price would later show.

The relationship between fiber and cholesterol

Fiber’s apparent utility can be seen in its ability to lower cholesterol levels. 

One review found that plant-based, high-fiber diets reduced LDL cholesterol (”bad” cholesterol) by up to one third.

This quality, however, isn’t as beneficial as it may seem. Many substances that are known to be toxic reduce cholesterol. High cholesterol isn’t usually a problem — and even when it is a problem, it usually indicates that some deeper underlying issue is going on.

Read our article on cholesterol and health if you’d like to learn more about this nuanced topic.  

The relationship between fiber and blood sugar

Fiber can also reduce the glycemic index of certain foods and help keep your blood sugar stable. Studies show that fiber’s ability to slow digestion can reduce blood sugar spikes by between 10 and 20%.

This benefit, however, is also limited by its context — most people eat far too many high-glycemic foods anyway. Fiber’s glycemic moderation becomes completely unnecessary when you eat a low carb  keto/carnivore diet.

What about fiber intake and weight loss?

The research on the link between dietary fiber with weight loss has also been unimpressive. Most studies so far have provided mixed results, and even the studies that do appear to show benefits have been poorly designed.

Even mainstream, pro-fiber researchers find that, “The limited number of clinical trials comparing high-fiber foods with low-fiber foods have not provided consistent data indicating that these diets are more efficacious for weight loss than low-fiber control diets.”

Far from the myth about fiber being beneficial, certain types of fiber can cause enough bloating and pain to interfere with weight loss. A popular fiber supplement and food additive called guar gum has been connected with abdominal pain, flatulence, diarrhea, stomach cramps, and more. 

A 2001 analysis looking at guar gum for weight loss found that “Guar gum is not efficacious for reducing body weight. Considering the adverse events associated with its use, the risks of taking guar gum outweigh its benefits for this indication. Therefore, guar gum cannot be recommended as a treatment for lowering body weight.” Again we see the fiber myth debunked. 

What does fiber do for your body?

While our bodies themselves can’t digest fiber, the bacteria in our large intestine can. These bacteria ferment fiber and create gases like hydrogen and methane.  The exothermic (heat-producing) reaction can also damage local organs and tissues. 

Fiber intake may even impair fertility. One study found that women who consumed large amounts of fiber were less fertile. And it can cause tremendous flatulence, to boot.  

As your fiber consumption goes up, so does your risk of developing diverticular diseases. One study found that people who ate more fiber and had more bowel movements also had a higher likelihood of colon disease.

Indeed when we take a closer look at the health=fiber myth, we see that fiber may actually be a junk food. One 2007 editorial about fiber and a colorectal disease called insoluble fiber “the ultimate junk food”, as it’s “neither digestible nor absorbable and therefore devoid of nutrition.”  

Another 2007 study found no relief from bowel polyps when study participants were placed on a high-fiber, low-fat diet.

What the new science says about dietary fiber 

Newer studies have further affirmed the view that many types of fiber are junk. 

A 2012 study published in the World Journal of Gastroenterology looked at fiber’s effects on constipation and concluded 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.”

Research has also revealed that excess insoluble fiber can bind to minerals like iron, zinc, magnesium, and calcium and prevent the absorption of these nutrients. Excess insoluble fibers can also inhibit enzyme activity enough to impair protein absorption, essentially acting as an antinutrient

The last bastion of fiber’s health benefits lies in its ability to boost the production of certain types of fatty acids. A percentage of soluble fiber gets fermented by gut bacteria into short-chain fatty acids like butyrate and proportionate. These fatty acids, in turn, can fight against neurodegeneration, cancer, and obesity.

Butyrate-fed rodent study

Butyrate-fed rodents appear resistant to weight gain. Image from Pubmed.ncbi

The fiber-butyrate pathway has led some gut health experts to continue recommending high fiber diets. 

What these experts miss, however, is that butyrate and other gut-friendly fatty acids can be obtained in much simpler and safer ways. Butter, yogurt, milk, cream, and other dairy products are all rich in anti-inflammatory butyrate — and, unlike fiber, they don’t cause gut irritation.  

Why fiber gets added to food

If fiber is so unhelpful, then why does it still get added to food?

Largely because official guidelines perpetuating the fiber myth lag behind the latest research.

Functional fiber continues to be added to processed foods as a way to increase fiber content and satisfy consumers who wish to meet these official guidelines. 

According to NPR, the demand for fortified foods is still there. Many health-conscious consumers still buy products that contain added synthetic fiber. Grain-based, high-fiber food products continue to be highly popular. 

The downsides of going fiber-free

If you’re ready to try out a low/no-fiber diet, there are a few things you should know. 

Making the shift may result in temporary changes to your bowel patterns. Many people who begin a carnivore diet find that their digestion slows down. This is normal and natural, but it might still take some getting used to. If you begin to experience carnivore diet constipation, ensuring adequate water and electrolyte intake can help. 

Another thing to keep in mind: some experts feel that following a VLC (very low carb) diet can harm both ‘good’ and ‘bad’ gut bacteria. So while beneficial in the short term as a way to reduce overgrowth of unhealthy gut bacteria, in the long term, a fiber-free VLC diet may be unhealthy. 

The theory follows that a VLC diet for long periods of time might harm the gut’s normal gel lining. Studies looking at Poland’s low-carb “optimal dieters” have unusually high rates of colon cancer. (Note that research does not support the idea that this link is anything but correlative.)

If you’re young, active, and happy with your body composition, you may want to experiment with adding small portions of raw  honey or fruit to your diet. Only a small amount of carbohydrates is needed to keep the digestive tract well ‘lubricated.’ If you’re trying to lose excess weight or maximize your natural fertility, feel free to ditch the carbs/fiber entirely for at least a few months. 

The fiber in low-carb berries may also boost your body’s production of short-chain fatty acids. Butyrate, in turn, can help maintain the integrity of your gut lining and keep your metabolic rate high.

Reducing fiber: what to expect

Better research leads us to a better solution for having healthy digestion than eating bunches of fibrous plant matter: focus on general health, and let bowel frequency take care of itself. 

Many people experience better digestion when they reduce their fiber intake — much to their initial surprise. You might experience easier bowel movements and reduced bloating/gas as you make the switch.  

One randomized controlled trial looking at the fiber myth followed 60 people with chronic constipation and IBS. It found that going fiber-free for just two weeks greatly reduced symptoms. Six months after the diet ended, 41 of the study participants had chosen to stay fiber-free and were still doing well. The ~20 participants who’d gone back to eating fiber regained their IBS symptoms.

Effects of Reducing Dietary Fiber

Image from Dr. Paul Mason

So what does this mean for our own consumption of fiber?

Looking back over the sum of the research, it’s clear that dietary fiber has been greatly overrated. Fiber isn’t usually beneficial — and large amounts of fiber can quickly become harmful. 

For these reasons, Dr. Kiltz recommends a no-fiber or low-fiber approach. Cut your insoluble fiber intake to a minimum. And if you do eat fiber, make sure it’s a soluble fiber from whole-food sources: 

  • Potatoes
  • Sweet potatoes
  • Fruits (especially low-carb berries)
  • Mushrooms

Small amounts of the above foods may keep your digestive tract well ‘lubricated’ and boost your body’s production of beneficial short-chain fats. Especially if you slather them in plenty of tallow or butyrate-rich butter.

If you don’t enjoy fruits and veggies, on the other hand, then don’t feel obligated to eat them. The research is clear that humans evolved to do best with a hypercarnivore diet centered around animal products. You can take a deeper dive into the human-carnivore question here

Animals, after all, have digestive tracts specifically designed to process plant fibers and convert them into more usable energy. Turns out Ron Swanson was both funny and right. 

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