In an effort to minimize toxins absorbed into the blood stream from the colon, mucus is created to encapsulate the waste of certain foods such as meat, dairy, white flour and other processed foods. This mucus build-up is a natural defense mechanism, and could be efficiently eliminated through the colon if it occurred only rarely. But people who eat mucus-producing foods every day create a toxic build-up of layers and pockets of mucus and decayed fecal matter, remnants of which can stay in the colon for 20 to 30 years or longer.
http://www.mnwelldir.org/docs/detox/detox.htm