Fiber Fallacies

Do you eat vegetables and fruits to get the “benefits” of fiber?

You might feel surprised to learn that not one experimental study has proven any beneficial effect or human requirement for fiber.

In terms of requirement, facts prove humans do not need fiber in the diet.

First, human breast milk contains no fiber, and infants have normal, healthy bowel function when exclusively breast fed – which by the way provides them with a high fat diet. In contrast, if fed high fiber foods, infants can experience colic due to accumulation of gas causing bloating of the intestine.

Second, several primitive groups, such as Inuit and Chukchi, eat or ate fiber-free diets and have or had no signs of illness, such as “constipation,” appendicitis, diverticular disease, or colorectal cancer commonly attributed to so-called fiber deficiency.

In fact, experimental studies (not epidemiological, which establish nothing) show high fiber intake to damage the gut and promote colon cell abnormalities.

“Disruption-Induced Mucus Secretion: Repair and Protection” explains how fiber damages the gut wall. The authors suggest this damage is “good” but Michael Eades has a different take on it in A Cautionary Tale of Mucus Fore and Aft.


Many people think eating a high fiber diet will prevent colon cancer; but we not only have no proof or even weak evidence that ingestion of fiber prevents colon cancer, on the contrary we have experimental evidence indicating that diets high in fermentable fibers actually increase colonic cell proliferation of the type that leads to cancer.

Lupton et al reported that a diet high in fermentable fiber increased cecum size and large intestine length, and reduced pH and stimulated cell proliferation, in rat colons. [J. Nutr. 118: 840-845, 1988.]

Jacobs and Lupton found that when they fed rats a high fiber diet based on either oat bran, pectin, or guar, the yield of proximal colonic adenocarcinomas increased by 4.5 to 5 times over the fiber free level. [Cancer Research 46, 1727-1734, April 1986]

Mandir, Englyst, and Goodlad found that when they fed mice fiber in the form of bran or apple pomace, both fibers significantly increased cell proliferation, number of polyps, and tumor burden born by the mice. Both fibers increased polyp diameter, bran by 243% and apple fiber by 150%. [British Journal of Nutrition (2008), 100, 711–721]

Generally, diets high in fiber make the feces softer and looser. A study by Inoue et al found “Soft or loose feces increased the risk for all subsites of colorectal cancer, particularly in female rectum cancer (odds ratio [OR] = 4.5)” [Cancer Causes Control 1995 Jan;6(1):14-22.]. Although epidemiological studies generally don’t carry much weight, when the odds ratio goes above 2.0, the association carries more weight. This finding of a greater than 4 fold increased risk of colorectal cancer in people with soft or loose stools suggests that high intake of fermentable fiber may promote cancer in humans as well as rats.

In their article “Fiber and colorectal diseases: Separating fact from fiction” published in the World Journal of Gastroenterology [2007 August 21; 13(31): 4161-4167], Tan and Seow-Choen review the physiological effects of fiber ingestion and evidence for beneficial effects of fiber. The facts include:

1. Fiber has no nutritive value. For this reason, of all carbohydrates, I would say that fiber perhaps most deserves the title “carbage.”

2. Fiber demonstrates antinutritive effects – blocking the absorption of essential nutrients. Another reason to put it in the junk food pile.

3. People eating high fiber diets demonstrate a greater risk of excessively long colons and a higher incidence of megacolon and volvulus (strangulated colon). This suggests that high fiber intake has a negative effect on colonic transit, actually facilitating impaction.

4. High fiber intake promotes bacterial growth and fermentation, which produces hydrogen, methane and carbon dioxide, causing cramps, bloating, and distension, all of which injure the colon.

5. Contrary to the predictions of Burkitt, Trowel, and other fiber fanatics, we have no evidence that increased fiber intake reduces diverticular disease; on the contrary “the incidence of diverticulosis and complications of diverticular disease have been increasing in the West despite increase in dietary fiber intake.”

6. We have no evidence that a human must have daily bowel evacuation of feces to maintain health of any body structure, colon included.

The volume and frequency of feces evacuation simply reflects how much indigestible matter you eat. The more carbage you eat, the more carbage you evacuate. On the other hand, if you eat a low residue diet – e.g. meat only – you may evacuate rather infrequently, simply because you don’t have any carbage to clear out.

“Infants on breast feeding are known to be able to go for long periods of time without any bowel movement. This is because the breast milk is thoroughly absorbed with minimal residue. Therefore, if an individual has a low residue diet and therefore less frequent bowel movements simply because there is less faecal material to evacuate, this is not pathological.”

“In other words, the more fiber one ingests, the more faeces one will have to evacuate. By the mass effect of the formation of more faecal material, there will be a resultant increase in frequency of evacuation. By increasing fiber intake, stool frequency and faecal weight will be correspondingly increased. However, this is a classic case of rubbish in, rubbish out only.”

On a side note, the larger and softer your stool, the more toilet paper you need to clean yourself. Who knows how many forests we can save by cutting down on fiber intake?

7. High fiber diets do not make it easier to evacuate. On the contrary, by increasing the bulk of the stool, a high fiber diet can make defecation more difficult, since the passage way out has a rather small diameter. Which leads to the next point….

8. People suffering from hemorrhoids and anal fissures should avoid high fiber diets. The large caliber of fiber rich stools contributes to straining on defecation, promoting hemorrhoids, and “Passage of large bulky stools will also result in direct trauma from stretching of the anal mucosa leading to anal fissures.”

In conclusion, fiber does not provide any of the benefits claimed for it, and has a number of deleterious effects rarely mentioned. I have experienced several of those ill effects first hand, most extremely when I ate a low-fat, high carbohydrate grain-bean-and-vegetable based diet, and to a much lesser degree when eating a plant-dominated hunter-gatherer style containing several pounds of produce daily. In the past year I have progressively reduced my intake of fibrous foods and so far I can say that every time I have cut down my carbage intake, my gut health has improved.

You might want to try it yourself.