THe component of whole-grains nute, fruits, and vegatables that is not able to be digested in the human digestive tract (GI tract). Fibre is primarily and celluose and lignin. Humans do not have the digestive enzyme cellulase and others required to use fibre as an energy source. Herbivores and certain insects can digest fibre with the assistance of their bacterial flora! Although we cannot use fibre for energy, it is still important in the diet as it adds bulk to the faeces. This helps constipation and also increases the peristaltic reflex (want a GI tract review? Click here !) in moving food along the intestinal tract.