Most people have some awareness of fiber’s important role in digestive health and its cancer-protective properties. Most fiber types do help us in some way, but many do not offer the broad spectrum of benefits carried by others.

The most beneficial type of fiber is called fermentable fiber. These plant molecules feed certain families of microbes and allow their populations to flourish, while generating short chain fatty acids (SCFAs) along the way. The SCFA butyrate is a critical type of fat that has been shown to not only improve the immediate GI environment, lowering the colon’s pH and helping nourish the cells that line the digestive tract, but to also help regulate gene expression in other areas of the body, and to even reduce a person’s systemic level of inflammation.

The differences between true, vegetable-based fiber and the types that are most often added to fiber-fortified foods are vast. Breakfast cereals and other products often have sawdust-derived cellulose or wheat bran added to reach their "high in fiber" status. Attempts to show that fiber-fortified foods offer protection against cancer for instance, have failed repeatedly. Vegetable fiber does, in fact, offer protection against a variety of common Western diseases, including breast cancer, whereas whole grains and cereals do not.(1)

It gets even murkier when you consider the results of rigorous investigations of cereal and grain fiber. A 1989 study, for instance, showed that men who adopted a recommended whole grain, high-fiber-cereal diet (17 grams or more of fiber coming from whole grains) had an increased rate of heart attack — 22 percent higher than men who ate a low-fiber (less whole grain) diet. This is exactly the opposite result expected by the investigators, and is most likely why they failed to discuss it in their conclusions!(2)

Fiber is impossible for us to digest, but can be of great value to some important microbes. If they can ferment it, then it can serve as a great source of assistance with everything from glycemic control to intestinal repair and healing.

If the fiber is not fermentable, then it can serve as the ultimate anti-nutrient, binding micronutrients and altering the GI transit time to produce anything from a general intestinal irritation to very loose bowel movements.(3)

This is why fiber has such a bad reputation in some clinical settings. In most cases, patients that experience extensive bloating, increased gastric reflux (GERD) symptoms, nausea, or altered bowel movements have been given a food that was either fortified or was high in bran content. As always, the best solution is to eat whole foods and products made with whole foods.

This paper, published in the American Journal of Gastroenterology, is one of the best overall resources for a thorough understanding of which fibers are best for our health.

  1. (Pietro Ferrari 2013)(Me´lanie Deschasaux1 * 2013)(Zhang CX1 2011)
  2. (Burr ML, 1989)
  3. (Janet Tomlin 1988)

Dr. John Bagnulo is Director of Nutrition at Functional Formularies, and leads nutrition and research and development initiatives. Learn more about Dr. Bagnulo here.