Image copyright Angela A. Stanton, PhD. Created by AI.
Do you eat foods rich in fiber? Why? Chances are, you are eating a fiber-rich diet because you have been told repeatedly it is healthy and essential, and you may have even heard something about the gut-brain connection and that it is very important to keep your gut in good health. But have you ever asked why your gut would need something that is not food? After all, your gut is the center for digestion and nutrient absorption of the foods you eat. Therefore, everything you eat is assumed to be digested and absorbed, yet most fiber is indigestible, and no fiber of any kind has nutrients for your body to absorb.
So why are we told to eat fiber? And is the need for fiber really true?
What is Fiber?
Fiber is a carbohydrate. However, unlike what typically people think carbohydrates are, such as table sugar, glucose, fructose, and starches, as in fruits and veggies, fiber is different. We may select our next meal for its sweet taste, pleasant texture, or because we know from experience that it is energy rich. We don’t seek out food items for their fiber content on our own without being “educated” by dietary experts of their “importance”. So, let’s examine how important fiber really is.
What is considered fiber is defined by the USDA and the FDA as follows:
“Dietary fiber that can be declared on the Nutrition and Supplement Facts labels includes certain naturally occurring fibers that are “intrinsic and intact” in plants, and added isolated or synthetic non-digestible soluble and insoluble carbohydrates that FDA has determined have beneficial physiological effects to human health. These effects include lowering blood glucose and blood cholesterol, reducing calorie intake, and increasing the frequency of bowel movements. The Nutrition Facts label final rule defines ‘dietary fiber,’ in relevant part, as ‘non-digestible soluble and insoluble carbohydrates (with 3 or more monomeric units), and lignin that are intrinsic and intact in plants; isolated or synthetic non-digestible carbohydrates (with 3 or more monomeric units) determined by FDA to have physiological effects that are beneficial to human health” (see here).
There are three types of fiber: soluble, insoluble, and resistant starch. While these are important classifications, there is no official, comprehensive USDA database for these components, and resistant starch is not included in the USDA Food Data Central (FDC) or the National Health and Nutrition Examination Survey (NHANES) databases at all. In fact, when looking at fiber content of a specific food in the database, there is no differentiation between soluble and insoluble fiber either; all fiber in a food item is just “fiber”. For the sake of information, I will explain the differences between fiber types and their roles.
Soluble fiber interacts with water and creates a “paste” that can provide sustenance to gut flora and may even taste good for your tastebuds—such as chia pudding, for example.
Insoluble fiber, as the name suggests, does not interact with water or fat. It is a tough substance that gives plant cells shape and strength. It is not possible to digest insoluble fiber by the battery-strength acid in our stomach, an acid that is strong enough to drill a hole through cement. Even weak acid, such as acid rain, can damage concrete (see here), so imagine how tough insoluble fiber is, if human stomach acid at pH 1-1.5, one of the strongest stomach acids in nature, cannot make a dent in it at all (see here). Digestive enzymes also don’t dissolve insoluble fiber; nothing digests insoluble fiber in our body. So insoluble fiber goes in through your mouth and comes out into the toilet without any change (digestion) or use (nutrient absorption) on your part. Whatever happens to insoluble fiber happens because of the bacteria in your colon, which can ferment it and utilize its carbohydrate. Insoluble fiber in the plants we are told to eat is basically “tree bark” that is still fresh so not yet hardened. For further information on this, a very basic article on fiber can be read here, written by Dr. Georgia Ede.
Image copyright Angela A. Stanton, PhD. Created by AI.
Resistant starch is created by cooking starchy foods, such as rice or potatoes, and refrigerating/freezing them once cooked. Resistant starch amount in foods can swing a lot based on the variety of the specific plant (like think how many potato types you can buy, and each has a slightly different ability to form resistant starch), ripeness, cooking time, cooling time, reheating, and fat content. The resistant starch amount also changes with the method it has been created. It is generally not mentioned in the government database.
Fiber as a Nutrient?
Nutrients are classified into the following categories:
- Macronutrients: Carbohydrates, proteins, fats
- Micronutrients: Vitamins, minerals
- Essential nutrients: A subset of macro and micronutrients that the body cannot synthesize and must be obtained from the diet. For example, vitamin C.
If you ask Google the question “is fiber an essential nutrient?” you will find the following standard answer:
“No, fiber is not technically considered an essential nutrient because the body does not have a specific deficiency-state for it, unlike vitamins and minerals.”
Dr. Google cites articles, like this, showing fiber being not essential, and also this, which says it is essential. I also searched for the definition of the term “essential nutrient” and what is meant by “nutrient” and I found this: “In biology, a nutrient is a substance that provides essential chemical elements or compounds for an organism’s growth, development, and maintenance of life” (see it defined in biology). Since any nutrient is only defined as a nutrient if it provides essential elements for the organism, and fiber doesn’t provide any essential elements, after all it is indigestible and no nutrients are absorbed from it, fiber is not a nutrient. And if it is not even a nutrient, it is definitely not an essential nutrient.
Why Are We Told To Eat Fiber?
If fiber is basically indigestible tree bark, not a nutrient, why are we told that we must eat it?
We are told to eat fiber because it does the following things:
“Fiber promotes a healthy digestive system by preventing constipation, helps with weight management by increasing fullness and slowing digestion, and can lower the risk of chronic diseases like heart disease, type 2 diabetes, and certain cancers. Fiber also aids in cholesterol regulation and helps maintain stable blood sugar levels, contributing to overall health and potentially increasing longevity.”
Let’s drill into each of the above claims and see if they are true.
Healthy Digestive System
When you search for the definition of what is meant by a healthy digestive system, you find the following:
“A healthy digestive system efficiently breaks down food into nutrients and energy, while also eliminating waste effectively… A healthy digestive system is characterized by regular bowel movements, minimal digestive discomfort, and efficient nutrient absorption.” Wikipedia defines it as “…the absorption of nutrients from food without distressing symptoms.” (see here)
I immediately see a conflict! Do you?
- On the one hand a healthy digestive system is one in which everything you eat is DIGESTIBLE and gives no distressing symptoms.
- On the other hand, insoluble fiber (INDIGESTIBLE)promotes healthy digestive system.
Either 1 or 2 can be true but not both. It follows that insoluble fiber fails the “healthy digestive system” definition.
Preventing Constipation
Image copyright Angela A. Stanton, PhD. Created by AI.
I don’t know about you, but I have yet to meet a person who is able to avoid constipation by adding more fiber. Most people who eat fiber struggle with constipation. We have a booming market of OTC laxatives and stool softeners to relieve constipation. Most laxatives use a slippery solution by adding polyethylene glycol, which pulls water into the stool and not more fiber, or stool softeners, which use docusate (dioctyl sulfosuccinate sodium), which dissolves water and fat in the feces to soften it, not fiber. It seems that by adding fiber to the diet, we created a problem, for which we invented various solutions for purchase.
How insoluble fiber works in your gut:
Insoluble fiber is a waste product that soaks up water in your colon. Since fiber is “plant stuff” by definition, it will absorb water and swell, creating bulk. The definition of bulk is as follows: a large quantity, volume, or mass of something. So, fiber makes your stool bigger, and therefore harder to pass. The last thing one would expect is that enlarging something will make it easier to pass…
Also, how does something that is indigestible “stimulate digestion”?
Wait…
Fiber can cause or worsen constipation if you don’t at the same time increase your water intake because fiber soaks up water, and without enough fluids, it can lead to hard, difficult-to-pass stools. To avoid this, they suggest to “slowly increase your fiber intake and drink plenty of fluids to support healthy digestion”… ouch.. you are already constipated because of too much fiber and now they are recommending what? Increase fiber slowly! Seriously?
Image copyright Angela A. Stanton, PhD. Created by AI.
Based on everyone’s experience I know: bulk = constipation. So, the last thing bulking your stool with fiber will do is help you eliminate better.
Weight Management
What exactly is weight management? Weight management refers to the process of achieving and maintaining a healthy weight through various strategies, including eating “right”, physical activity, and lifestyle modifications.
Eating Right:
Since “eating right” is a very long and special topic on its own, this article simply mentions that the way weight management is referred to (in the definition of what is a benefit of consuming fiber) is that if you eat fiber, it fills up the stomach and gut space, so you eat less. This is based on the argument of CICO, of which I wrote extensively here. In sum: fiber’s role here is the same in “eating right” as eating paper instead of a meal. It fills up the stomach with zero nutrition.
Physical activity:
Studies show that people following modern Western lifestyles burn about the same total calories as ancestral active people, despite much less physical activity (see here and here and here). Furthermore, most people didn’t exercise voluntarily prior to the 1960s. The first exercise programs started with running and jogging in the 1960s and then in the 1970 the “gym” era started. Although people didn’t exercise, none of the chronic diseases that we today blame on the lack of exercise was widespread or even existed. So where on earth does the idea come from that the lack of physical activity is one of the causes of these modern diseases? Today millions exercise regularly. In the US alone, it is estimated to have ~95,000 gyms, and health and fitness clubs in 2025, and millions of Americans exercise (see the numbers here). Physical activity (barring extreme cases) clearly has absolutely nothing to do with weight management.
I am not saying that physical activity is bad. What I am saying is that it has nothing to do with fiber and weight management.
Lifestyle modifications:
Getting enough sleep, managing stress, and avoiding unhealthy habits like smoking. Yep, everyone is working toward achieving these goals. But note: these are typical normal human “goals” that existed prior to the 1960s as well—think WWI and then WWII… just how much sleep did people get? And from the movies we watch: there was hardly a person for 5 minutes without a cigarette in their mouth. I am not saying that smoking is healthy…
What I am saying is that “getting enough sleep, managing stress, and avoiding unhealthy habits like smoking” is a fluff statement, independent of fiber and weight management.
Increasing Fullness and Slowing Digestion
“Fiber increases fullness by adding bulk to meals, which stretches the stomach and slows digestion to delay hunger.”
Woohoo! SLOW THINGS FURTHER BABY!! Already constipation? No problem!! Just let’s add more time for the feces to grow bigger and harder in the colon!
Seriously? Is this a good thing?
Slow digestion is gastroparesis. Symptoms of gastroparesis include nausea, bloating, belly pain, feeling full after eating just a few bites and long after eating a meal, acid reflux, not wanting to eat, weight loss and not getting enough nutrients—yep! Exactly what happens when eating insoluble fiber.
Can Fiber Lower the Risk of Heart Disease, T2D, & Certain Cancers?
This was a very curious question because I knew that an automatic answer must follow: Insoluble fiber can lower the risk of heart disease, T2D, and certain cancers “by promoting regularity, reducing cholesterol absorption, and minimizing the time harmful substances spend in the intestines”.
I highlighted the two parts in the above to show you the inconsistencies. I have already shown that fiber increases bulk, which is essentially a plug in the colon, which not only doesn’t promote regularity but increases irregularity and can be the cause of serious constipation.
By reducing the speed with which the food passes through the gut, fiber increases transit time, thereby encouraging toxic substances to stay longer in our gut. Fiber cannot at the same time slow down the speed (increasing transit time) and shorten the time (decreasing transit time) the harmful substances spend in the gut.
Cholesterol Regulation
How does insoluble fiber regulate cholesterol? It actually doesn’t. Soluble fiber does, by binding to bile acids and cholesterol in the small intestine, preventing their absorption and promoting their excretion from the body. Whether this is beneficial or not can be debated and is beyond the scope of this paper.
What Have We Learned?
- Fiber does not prevent constipation but increases the chance that you end up with one.
- Fiber does not help with weight management—it may fill the stomach with zero nutrition, causing malnutrition, and it may also increase weight—feces is heavy.
- Fiber does indeed increase fullness—often to the level of gastroparesis, an unhealthy state.
- Fiber can’t lower the risk of heart disease, T2D, or certain cancers. For this read further here.
Before I end the discussion on the importance of fiber, one very interesting story must be brought to your attention.
The Zero-Fiber Vilhjalmur Stefansson Experiment
He was an arctic explorer in the early 20th century, who lived with the Inuit for several years, eating only animal products, and then upon returning to the mainland in 1928 he underwent a 1-year in-hospital animal-products only diet (carnivore diet) with a colleague. Under full medical supervision, he and his colleague lived in Bellevue Hospital in New York before continuing the experiment at his apartment, all while being monitored by medical professionals and while all their foods were provided to them.
The doctors found that after a year on the carnivore diet, neither Stefansson nor Andersen suffered from high blood pressure, kidney trouble, or vitamin deficiencies, as some experts had predicted, in spite of not taking any supplements.
Since for a whole year the two men ate nothing but animal products, no fiber at all, and they remained very healthy (see here, here, and here), they showed that there is no need for fiber in the human diet, on an all animal-based diet, when plants are not consumed. Just simply based on this single study, which we really can consider the first human clinical trial of the carnivore diet, we can see that the statement that fiber is essential is not at all true.
Context matters! If you eat plants in your diet, then you must have fiber with those plants. All of the clinical trials that show beneficial effects of fiber, compare low fiber diet to high fiber diet, both containing plants. The only correct clinical trial without fiber is the Stefansson experiment without any plants.
Summary
Should you eat fiber? The answer is completely up to you.
Do you need to eat fiber for health? No, not as long as you don’t eat any plants. So, if you are on the carnivore diet, don’t supplement fiber. You are better off without it. But if you eat plants: make sure you eat whole plants full of fiber.
Is fiber a nutrient? Nope. It is a waste product.
Is fiber essential? Nope. It is a waste product.
Comments are welcome, as always, and are moderated for appropriateness.
Angela
Clueless Doctors & Scientists 