Constipation

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Question Received:

  1. What does the most recent epidemiological evidence suggest about the consequences of constipation, and the value of NSPs in the diet?

Response:

What does the most recent epidemiological evidence suggest about the consequences of constipation, and the value of NSPs in the diet?

1st April 2000

Constipation is one of the most common chronic digestive complaints, affecting about 2% of people in industrialised countries. However, it is best regarded as a symptom of a disorder rather than a disease in its own right. Because there is considerable variation in 'normal' bowel habits from one person to another, it is difficult to define constipation in a precisely objective way for the purpose of gathering epidemiological evidence.

Constipation is generally considered to increase with advancing age, and indeed the number of recorded cases rises rapidly in people of 65 and above (eg: Abyad and Mourad, 1996). However, it has been pointed out that it may be the self-diagnosis of constipation and the use of self-prescribed laxatives that increases rapidly with age, rather than the occurrence of clinically-defined constipation (Harari, Gurwitz, and Minaker, 1993). Constipation is apparently more common in women than in men, in nonwhites than whites, and in people from families with low income (Campbell, Busby, and Horwath, 1993).

Several factors are linked with the causation of constipation. These include behavioural, endocrine, neurogenic and drug-related processes (Binder, 1988). Insufficient dietary fibre is is probably a major precipitating factor in developed countries where the diet contains a high proportion of industrially refined and processed foods (Camilleri et al, 1994). Changes in colonic motility can occur as a result of neurological factors such as damage to the pelvic floor during childbirth, pelvic surgery, exposure to environmental toxins, or exposure to an infectious agent, and these may also contribute to particular instances of constipation. In older people, additional risk factors include inactivity, depression, confusion, medication, cultural influences, and neuromuscular changes. Although colonic transit time does not appear to change significantly during aging, anal sphincter pressures decline (Wald, 1993). Constipation is a frequent complication in patients being treated for advanced cancer. This can be a consequence of reduced food intake, general debility, and medication with opioid analgesics (Sykes, 1994; Mancini and Bruera, 1998). For a review of the epidemiology, causes, and treatment of constipation in infants and children see Fotter (1998). In terms of pathophysiology constipation can be divided into different categories such as normal transit and slow transit (Kamm, 1992; Velio and Bassotti, 1996), but the underlying biological processes in each case are incompletely understood.

Chronic constipation may be accompanied by relatively few symptoms, or it may have more serious consequences such as impaction and ulceration giving rise to pain and inflammation, perhaps followed by obstruction of the bowel. Some people with chronic idiopathic constipation are sufficiently disabled by their symptoms to require an operation such as subtotal colectomy (Ghosh et al, 1996).

To treat constipation, non-pharmacological measures are to be preferred initially. These include making sure that adequate fluids are being taken daily, behavioural modification such as increased mobility and exercise, and an increased intake of dietary fibre. Counselling may be required to emphasise that daily bowel movements and purging are not essential to good health (Passmore, 1995). If these measures are not effective, then the use of laxatives can be considered. However, it has been reported that the use of stool softeners, magnesium hydroxide ('milk of magnesia') and stimulant laxatives is difficult to justify from the available observations about their effects (Lederle, 1995; Corazziari, 1999). As they enter their later years, many people become concerned that they may have constipation and self-treat excessively with over-the-counter laxatives. This can produce new problems. Alternative therapies are being tried with some success. For example biofeedback therapy is an effective treatment for some patients (Kamm, 1992), and abdominal massage therapy is being revived (Ernst, 1999).

"Dietary fibre" includes a range of mainly indigestible substances mainly composed of cellulose and non-starch polysaccharides (NSPs) such as pectin and lignin. These materials are derived predominantly from the fruits, nuts, cereals, vegetables (especially peas and beans), and bread in our diet. Within the digestive system, dietary fibre assists the movement of faecal material along the large intestine, and affects the way the body absorbs and uses nutrients. It absorbs some water, thereby bulking up the faecal mass. A diet which provides around 20-30 grams of dietary fibre, or 12-24 g of NSPs, will help prevent constipation in adults. Other possible effects of fibre include lowering of blood cholesterol, a reduction in hunger, and possibly a reduction in colon cancer (Spiller, 1994).

The demarcation between dietary fibre and starch is not clear-cut. For example, there are "resistant" types of starch that pass through the small intestine unchanged and are then partially fermented in the colon by the resident micro-organisms (Cummings and Macfarlane, 1997). Since they influence the processes occurring within the large intestine, resistant starch can be classified alongside dietary fibre and NSPs.

Intestinal bacteria have other roles besides extracting useful carbohydrates from otherwise insoluble fibres. For example, they synthesise the vitamins B and K and metabolise bile acids and other sterols. So in the presence of NSPs and resistant starch, the beneficial bacteria thrive and we benefit from the materials they produce (Macfarlane and Macfarlane, 1997).

Dietary fibre and NSPs are thought to protect against bowel cancer by increasing faecal weight, diluting the concentration of potentially damaging chemicals in the faeces, and speeding up the movement of faecal matter through the bowel (Harris and Ferguson, 1993; Bingham, 1990; Cassidy, Bingham, and Cummings, 1994; Govers et al, 1999). Epidemiological estimates suggest that up to 80% of colorectal cancer is attributable to diet. There are high rates of bowel cancer in populations consuming diets high in meat and fat, and low in starch, NSPs, and vegetables (Bingham, 2000). It is of some concern that the proportion of fibre in the diets of people living in industrialised countries is on average only about half the recommended level.

References

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