Fiber Is “Not Essential”, But We Need Fiber. Nutritionists Agree.

I was challenged that fiber is “not essential”. Here’s my scientific opinion.

The background

I was challenged that fiber is a “not essential” nutrient for our body and that this is not commonly known by people. I agree. Even nutritionists rarely talk about fiber as a nutrient.

What is a nutrient?

This question is highly debated. The general consensus is that carbohydrates, protein, and fat are the macronutrients; whereas vitamins and minerals are micronutrients. These nutrients consistently being absorbed by the body and can support growth. Now, consider the following:

Is water a nutrient?
Is alcohol a nutrient?
Is air or oxygen a nutrient?

Whilst our body absorbs water, alcohol, and oxygen (from the air), and is involved in the function of growth, we hardly refer them to as nutrients. Hence, questioning what is a nutrient, sometimes can be a problem of interpretation of the English language.

The challenge:

Fiber is not essential. Hence, the human body has “zero-requirement” for fiber.

My view summarised in one sentence:

Whilst fibre may not be essential, the human body requires fiber to improve bowel movement, the excretion of cholesterol, and nourish the gut microbiome.

Details are explained.

Fiber

What is fiber?

Scientists define fiber as a non-digestible form of carbohydrate. The British sometimes call it “roughage”, referring to the coarse fibrous plant materials that are indigestible. It exists in almost all plant-based foods but absents from animal-based foods. Although whole grains are one of the best sources of fiber, you can also get fiber from low-sugary fruits and vegetables, as well as nuts and legumes. Since our body doesn’t have the right enzymes to digest fiber, fiber binds with other undigested materials, moves along the intestine, and passed out as stool.

Is fiber truly not essential for the body?

I was initially surprised by the fact that an author actually raised this to me, it has been addressed in a Medium article elsewhere. I never view fiber as not essential. But, perhaps it is good to do some reading to understand the origin of the view.

Curiosity led me to check how many people have expressed the view on the web. On Reddit, I am surprised that those who supported fiber is not essential for the body are also providing information about the keto diet. The main reasons are:

“Fiber deficiency” does not cause any specific diseases.
Diseases normally associated with “fiber deficiency” are also associated with the modern diet that is high in sugar.
Fiber is not absorbed by the body to perform physiological functions.

A search on Google Search engine for keywords (“keto diet” OR “low-carb diet”) AND “fiber” consistently show keto diet contains fiber. Most people believe keto diet requires fiber. However, the minority argued that fiber is not essential, a little known fact to “fiber supporters”.

Who cannot eat fiber?

Unless you have bowel issues, such as inflammatory bowel diseases (IBD), or before and after bowel surgery, there is no other information that supports the substitution of fiber to other dietary constituents.

In regards to IBD, the recommendation for fiber intake is changing. It was once questioned whether fiber-induced gut inflammation is a cause or consequence of IBD. However, it is now known that fiber does not cause the onset of IBD, and may even associate with a delay in the onset of IBD in individuals who are susceptible to it. The modern diet rich in saturated fat and sugar may be more related to the onset of IBD.

In individuals with an existing IBD, diet low in FODMAPs (fermentable oligo-, di-, and monosaccharides and polyols) is more promising when compared to total fiber-restriction. If you have an existing IBD, do talk to dietitians about the low FODMAPs diet. It is a more complicated diet, but you are allowed to enjoy a more variety of food when compared to total fiber-restriction.

Does fiber cause intestine abrasion or inflammation?

Allow me to quote one of the original text I read from Medium:

Fiber essentially irritates the walls of the intestines by cutting their sensitive lining. This irritation causes the intestines to secrete more mucus than usual to sooth the lining. The mucus, in turn helps the undigestible matter through your system and into the toilet.

FIBER! What is it Good For?

Absolutely nothing!

medium.com

Unfortunately, I could not find any scientific report that explains how fiber causes irritation, unless among those with IBD. I was fascinated by the way this sentence was framed, but I could rephrase the text into the following:

Fiber moves along the intestinal wall, resisting the digetsion. Fibre, especially the insoluble fiber, absorbs water from the intestine to soften the indigestible materials, whereas intestinal mucus wrapped around the indigestible materials to smoothen its passage through the intestine, reduce the risk of constipation and colorectal bleed during defecation.

Both texts sound reasonable, and seemingly legitimate. Perhaps, the same mechanism can be explained using different language and evoke different emotional responses to those who read it.

Who says fiber is bad?

The most frequently cited reference related to “fiber is bad for the gut” can be traced back to a book written by Konstantine Monstyrsky, titled “Fiber Menace”. While it is true that fiber causes gas, hence flatulence, it does not irritate the intestine in the general population without IBD.

Monstyrsky is a trained pharmacist but has not published any scientific publications. Although I have not read his book, I am highly skeptical about the content. It is true that in the field of nutrition, you often find contradicting information, i.e. “saturated fat bad for heart or not”, “does food addiction exist”, “should we restrict digestible carbohydrate as much as possible”, etc, but you will not find any scientific publications that agree with Monstyrsky’s view.

Source: https://www.gutsense.org/fiber-menace/about-fiber-menace-book.html

Requirement for fiber

Fiber may not be essential if abide by the strict definition of what is essential for the body. However, we prefer to have fiber in our diet as it improves the health of the general population.

A recent Lancet article published in 2019 systematically review the role of carbohydrate quality on indicators of health among people who do not have any chronic disease and found that 25–29 grams of fiber intake are associated with the best health outcome, including lowering body weight, blood cholesterol, blood glucose, and blood pressure. Consuming more fiber means larger stool. It dilutes any ingested cancer-causing agents and reduces the contact between cancer-causing agents and the intestinal cells. Therefore, a higher intake may be protective against colorectal cancer.

In contrast, It is also known that constipation is not always associated with fiber intake. However, dietary fiber or supplementary fiber and water are a standard prescription for those who experience constipation to smoothen bowel movement in clinical practices. Other recommendations to improve bowel movement include exercise that involves stretching of the body (yoga). Ironically, the cause of constipation often remains a mystery, known as idiopathic constipation, with 14% of individuals have chronic idiopathic constipation.

Of course, being said that fiber is not essential (even for gut movement). What is currently less understood is the role of diet in gut microbiota. Scientists believe that fiber is essential to feed gut microbiota, and that gut microbiota may return us with a range of benefits. A list of connections between gut microbiota and human physiology was previously described in a Medium article:

Gut Microbiota: An Entity That Connects to Distant Organs

Gut microbes intertwine with 12 organs of its host and they are revolutionizing healthcare.