Fibre, or roughage, refers to the non-digestible carbohydrates in vegetables and to a lesser extent in fruit. Fibre may actually be 'fibrous', as in celery, or may be a powder, or, when mixed with water in the intestines, a jelly. Fibre provides:
Bulk
Lubrication, and
Nutrition for friendly bacteria in the colon.
When fibre is combined with water, it swells up and provides bulk to the digestive system. This makes it easier for food to pass through the intestines. Food also passes through the digestive system faster, so that waste products are retained for less time in the body.
Some fibre has the effect of lubricating the contents of the intestines and, therefore, makes the food pass through easily and in a timely manner. The benefits here are the same as for bulk.
In addition, friendly bacteria in the colon feed on fibre and they are therefore nourished by it. By helping these friendly bacteria, we enable them to help us to digest food. Also, by giving them support, they are more able to exclude other, less friendly bacteria, from our colons.
Fibre is, therefore, necessary for a healthy and efficient digestive system.