Is All Fiber Created Equal?

One of the most confusing topics in GI and GI nutrition is fiber. Fiber is promoted by medical practitioners, holistic and traditional alike, as the answer to most lower GI problems, from constipation to diarrhea, to abdominal pain and bloating. For a lot of people, however, fiber is not the answer. In fact, fiber makes them feel worse. Lets try to understand the topic of fiber in a little bit more detail.

Fiber is the indigestible part of plant foods, made up of chains of carbohydrates that are too complex for human digestive enzymes to break down. In general, fiber is an important part of a healthy diet as it feeds beneficial gut bacteria and supports GI health. BUT…. Not all fiber is created equal. Fiber comes in two varieties, soluble (in water) and insoluble (in water). To make matters more complicated, the same type of food may contain both, soluble and insoluble fiber.

Insoluble fiber is generally poorly digestible. It adds bulk to stool and is generally recommended to people with constipation. However, people with constipation (or slow motility) may not be able to move that bulk along the GI tract. Instead, because of slow innervation of the GI tract by the autonomic nervous system, fiber accumulates in the intestines. It draws water into the intestines along with it and causes bloating. Many people with slow transit constipation complain of severe and intolerable bloating when they eat a high fiber diet. In addition, as fiber sits in the intestine without moving it serves as a food source for gut bacteria. Gas produced as a byproduct accumulates and causes even more bloating. People with irritable bowel syndrome similarly may have trouble handling insoluble fiber – these people are very sensitive to any amount of GI tract distension so anything that triggers bloating or gas causes a significant increase in abdominal pain.

Soluble fiber, on the other hand, is easier to digest. It absorbs water and may therefore firm up diarrhea in some cases. It also produces a sense of fullness as it forms a gel-like substance in the stomach thereby lowering blood cholesterol and sugar levels.

If our goal is to limit abdominal pain, discomfort, bloating and gas we need to be mindful of consuming too much insoluble fiber and instead choosing foods that contain soluble fiber. Tolerance for insoluble fiber is different for different people and is usually discovered through trial and error. Even a healthy person with no GI issues can reach a threshold of fiber tolerance and develop those same symptoms as people with IBS and constipation. Therefore, it is always a good idea to experiment with different types and amounts of food while paying attention to your bodily signals in the form of bloating, gas, gurgling, loud stomach noises, belching and nausea, all of which may be a sign that you have injected more fiber than you are able to tolerate.

My general fiber recommendations are as follows:

Cooked vegetables are generally easier to digest than raw vegetables. Cooking vegetables may decrease the amount of insoluble fiber.

Limit very tough cruciferous vegetables such as kale and brussels sprouts

Reduce the amount of seeds such as chia and flax. While chia contains both soluble and insoluble fiber, it is 85-93% insoluble fiber. The same goes for flax – about 70% of flax seed is insoluble fiber.

Limit nuts. Nuts are mostly made up of insoluble fiber.

Good sources of soluble fiber include: oats, barley, avocado, zucchini, cucumber, root vegetables.

Most importantly, be tuned into yourself and your body’s responses to what you are eating. People are different and there is no one dietary recommendation which would fit everyone. Fiber tolerance will be affected by the motility of your GI tract, your genetics, exposure to medications such as antibiotics etc. Let your body guide you.