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Constipation is a symptom that means different things to different people. Most commonly, it refers to infrequent bowel movements, but it can also refer to increased firmness of stool, the need to strain to pass a motion, and a sense of incomplete evacuation, or the need for laxatives, suppositories or enemas to maintain regularity.
Bowel movements once a day are ideal, but there is great variation in what is considered normal. Bowel motions anywhere between 3 times a day to 3 times a week are still within normal limits. Irritable bowel syndrome is a condition where features of constipation may exist with pain related to colon spasm. Slow-transit constipation is where to time taken for the stool to pass through the colon is documented to be excessively delayed.
Role of diet and exercise
Normal bowel movements are affected by diet, therefore someone who eats very little may not have a bowel movement for a week without experiencing discomfort or harmful effects. Normal bowel habits are affected by diet. The average Australian diet includes only 12-15g of fibre per day, which is half the recommended amount of fibre for proper bowel function. Eating foods high in fibre, including breakfast cereals (Weet-Bix®, ALL-BRAN®, and shredded wheat), whole grain breads and fresh fruits and vegetables will help provide the 25 to 30 grams of fibre per day recommended for proper bowel function. Exercise is also beneficial to proper function of the colon.
What causes constipation?
There are often multiple causes for constipation, including inadequate fluid intake and fibre, lack of exercise and environmental changes. Constipation may be aggravated by a change in diet, long periods of travel, and pregnancy. In some people, it results from chronically ignoring the urge to have a bowel movement.
More serious causes of constipation need to be excluded before a diagnosis of constipation is made. These include narrowings in the colon caused by repeated attacks of inflammation from diverticular disease or a cancer of the colon. Obstruction to defecation can also occur at the anorectum and this can be due to weakness of the pelvic floor and wall of the rectum resulting in the rectum collapsing on itself (intussusception) or ballooning out (rectocele). Other medical causes include a lazy bowel where there the normal bowel movements (peristalsis) of the bowel are impaired resulting in slow passage of stool along the colon (slow transit constipation).
What medications can cause constipation?
Many medications, including opioid-based pain killers, antidepressants, tranquilizers, and other psychiatric medications, blood pressure medication, diuretics, iron supplements, calcium supplements, and aluminium-containing antacids can slow the movement of the colon and worsen constipation.
When should I be worried about constipation?
Any persistent change in bowel habit, increase or decrease in frequency or size of stool or an increased difficulty in evacuating warrants a review by your GP, and a digital rectal examination.
Who should have a colonoscopy?
You should also be referred to a colorectal surgeon who will organise a colonoscopy if this has not already been done. If blood also appears in the stool, then this should be done sooner rather than later.
What other investigations are needed if colonoscopy is normal?
If colonoscopy is normal, then other tests may be needed to determine the cause of constipation. “Marker studies,” in which the patient swallows a capsule containing either radiolabelled or opaque numbered markers that show up on x-rays taken repeatedly over several days, help to confirm a lazy bowel (slow-transit constipation).
Other physiologic tests evaluate the function of the anus and rectum. These include tests that measure the innervation of the anus (pudendal nerve studies), the function of the anal muscles (endo-anal ultrasound and manometry), or x-rays that measure the emptying capacity of the rectum on straining (defecating proctography).
In many cases, no specific anatomic or functional causes are identified and the cause of constipation is said to be nonspecific.