When a low residue diet is taken, this time is doubled, the muscular contractions of the bowel are increased and the inside pressure is raised. It is this rise in pressure which is believed to produce the herniation which causes the diverticula.
They usually involve the lower portion of the colon or the large bowel but may involve its whole length. When diverticula are present, the condition is properly called diverticulosis.
There may be no symptoms at an early stage. However symptoms such as lower abdominal pain, distension and flatulence or an excess of gas in the bowel lead to the condition being called painful diverticular disease.
It is important for the doctor to distinguish between these three distinct stages because the presence of diverticula is so common in those over middle age. Any X-ray of the bowel may show their presence but they may not be the cause of the symptoms.
In diverticulitis, the symptoms are more marked and, in acute attacks, there may be severe lower abdominal pain associated with fever. Diarrhoea or constipation may be present.