There are two kinds of fiber, soluble and insoluble, and neither contains calories. Soluble fibers are able to dissolve in warm water; this means that they are able to absorb a lot of water and other particles. Insoluble fibers are not able to dissolve in warm water. While soluble fiber is often in the news due to its benefits in heart health, insoluble fiber deserves equal attention.
Insoluble fiber can be found in fruits, vegetables, grains and beans and benefits us in two very important ways. First, it adds bulk to our stool so that we feel an urge to go to the bathroom. This is important because our bowel is a muscle and like every other muscle in our body, it needs regular exercise to maintain its function. How our bowel gets exercise is by having bowel "movements." Without insoluble fiber, the bowel does not get enough exercise, leading to fewer bowel movements and eventual constipation. Hemorrhoids may also be a side effect of not enough insoluble fiber because of the strain needed when bowel muscles do not move very often and get out of shape.
Another benefit of insoluble fiber is that it can help our gut bacteria grow. Our gut bacteria, or gut flora, are living organisms that eat sugars and fiber, and prevent bad bacteria from living in our gut and making us sick. Insoluble fiber is a strong fiber that takes a lot longer for our gut bacteria to break down, which helps them grow and multiply.
So yes, we really do need insoluble fiber. Make eating fruits, vegetables and whole grain a part of your daily routine and see the benefits on a regular basis.