I can hear the titters now. But, seriously, do you have a deficiency of wood fiber in sawdust, i.e., cellulose?

No? Then why do people follow the common advice to include breakfast cereals such as All Bran, Fiber One, and Raisin Bran that, yes, are rich in fiber, but mostly rich in the cellulose fiber that is a constituent of sawdust? Cellulose in small quantities, as occurs in green vegetables and fruit is harmless, perhaps modestly beneficial. But there is no need to “supplement” with large quantities, as occurs with such bran or fiber-rich cereals. Nobody suffers from lack of cellulose.

Cellulose fiber undoubtedly bulks up bowel movements, as humans lack the digestive apparatus to break it down. Likewise, very little cellulose is broken down by bowel flora. Cellulose therefore simply passes through the gastrointestinal tract, inert and undigested, while exerting a mild damaging abrasive effect on the delicate intestinal lining in its passage when consumed in high quantities.

The discussion surrounding fibers has been confused by the more recently appreciated fact that fiber is not just one thing, but several different varieties. Just as “nutrients” can mean everything from vitamin C in citrus fruit to vitamin K2 in fermented dairy products to carotenoids in yellow/orange fruits and vegetables, so can the term “fiber” refer to a range of different things.

The popular notion of fiber is therefore that of cellulose. The poop-bulking effect of cellulose can fool you into thinking that you have achieved bowel health. In the case of wheat and grains, for instance, wheat germ agglutinin and gliadin peptide fragments are toxic to the intestinal wall, block gallbladder and pancreatic function, and induce alterations in bowel flora. Cellulose and phytates bind minerals, such as iron and zinc, and make them unavailable to you. But the cellulose provides the appearance of bulky stools despite the toxic damage incurred, causing you to believe that you’ve had a healthy BM. It is clear that the cellulose fibers of grains do not provide protection from colon cancer, despite the popular belief that they are protective. (The studies that document the health benefits of fibers did not break them down into the various forms, lumping all fibers together.)

We therefore need to get rid of the notion that cellulose fibers are necessary for gastrointestinal health. There is, however, a form of fiber that you will miss when you eliminate grains: arabinoxylan. Minus wheat and grains in your diet, you will lose about 3 grams per day of this beneficial (I hate to admit!) indigestible but prebiotic fiber, i.e., a fiber that is indigestible by you but is metabolized by bowel flora. Because most people obtain only a total of 8-9 grams per day of this hugely beneficial class of prebiotic fibers that nourish bowel flora, losing the 3 grams per day of arabinoxylan can yield constipation, abdominal discomfort, result in metabolic distortions such as higher blood pressure and blood sugar, and increased potential for colon cancer.

So, if there is a fiber to replace, it is to amp up your intake of prebiotic fibers. Even better, increase your intake to a level higher than the average 8-9 grams per day intake to the ideal intake of 20 grams per day. We accomplish this by adding foods such as raw potatoes, green bananas, and small servings of legumes to our daily routine, as detailed in this Wheat Belly Blog post.

We therefore need to rid ourselves of the notion that wood fiber—cellulose—is necessary for health, and replace this with the notion that our bowel flora require a specific class of prebiotic fibers to support the health of their host, i.e., you. Take care of your bowel flora and they will take care of you. By obtaining a healthy intake of such prebiotic fibers, you not only achieve bowel health and regularity without adding cellulose, but you also enjoy wonderful metabolic benefits, as bowel flora metabolize these fibers to metabolic mediators, such as butyrate, that reduce blood pressure, reduce insulin and blood sugar, raise HDL, reduce triglycerides, reduce LDL values, improve mood and reduce anxiety, and deepen sleep.