Introduction

Irritable bowel syndrome, chronic constipation and diverticular disease all arise from disordered peristaltic function and are at least partly attributable to the highly refined Western diet. These disorders could be regarded as endemic in developed societies.

Irritable bowel syndrome causes distressing abdominal discomfort in younger patients, whilst chronic constipation affects people of all age groups. Diverticular disease is probably caused by long-term dietary factors. These disorders make substantial demands on the time of family practitioners, physicians and surgeons, yet they are largely preventable. A hundred years ago, they were largely unknown in the West (apart from an obsession with constipation), as they still are in rural communities in many developing countries.

In addition to treating symptoms, the main surgical significance is that these conditions must be distinguished from inflammatory bowel diseases in the young and large bowel cancer in the older population. They have several symptoms in common:

Sigmoid volvulus is an acute condition resulting from chronic dilatation of the sigmoid colon plus an acute twisting of the sigmoid loop on a narrow mesentery, resulting in obstruction and massive dilatation (see below, Fig. 29.1, p. 378–379).

Angiodysplasia of the large bowel and ischaemic colitis are vascular conditions of the ageing gut, and both usually present with rectal bleeding and pain. Again, colorectal cancer has to be excluded as the cause of bleeding.

Epidemiological observations

Little scientific attention was paid to diet-related disease until the 1970s, although Gaylord Hauser had written about fibre in the diet in the 1930s. In the 1970s, the ideas of Surgeon Captain T. L. Cleeve, a Royal Navy physician, and later the remarkable epidemiological observations of Denis Burkitt, a long-time missionary surgeon in Africa, emerged. Now the subject of diet is respectable in surgical circles and has contributed to the understanding, prevention and management of many common diseases. Diseases such as irritable bowel syndrome, diverticular disease and appendicitis, common in Western society, are largely unknown in much of the developing world and this difference is almost certainly diet-related. Thus it follows that a dietary history is important in evaluating these patients, and dietary change is often a fundamental part of management.

Over millions of years as ‘hunter-gatherers’, humans subsisted on a staple diet of an extensive variety of vegetables and fruits, grains, legumes and nuts, supplemented by occasional meat or fish. The modern human gastrointestinal and metabolic systems are thus perfectly adapted to that diet. During the brief period (in evolutionary terms) of the last 100 years, the average Western diet has changed dramatically, due to affluence, fashion, convenience, food processing and advertising. Since the 1980s there have been similar dietary changes in the more prosperous parts of developing countries, particularly in the cities. The modern diet contains many more calories than the hunter-gatherer diet. These are largely in the form of refined carbohydrates and fats, especially saturated animal fats and ‘trans’ fats in artificially hydrogenated vegetable oils. Perhaps equally important, the modern diet contains far less non-absorbable fibre residue.

Mechanisms of disease caused by modern diet

Whilst the increase in calories and nutrients has brought benefits, it has also brought problems. The modern diet adversely affects both bowel function and metabolism, particularly of lipids. Box 29.1 outlines the important ways in which modern diet can induce disease and dysfunction. With regard to bowel diseases, the most important diet-related factors are likely to be faecal volume and consistency, together with gastrointestinal transit time. The average Western adult passes between 80 and 120 g of firm stool each day with a transit time of about 3 days, although transit time can be as long as 2 weeks in the elderly. In contrast, rural dwellers in the developing world, with a diet similar to the hunter-gatherer, pass between 300 and 800 g of much softer stool each day, with an average transit time of less than a day and a half.

Dietary fibre content

An essential part of managing many bowel conditions (other than irritable bowel syndrome) and preventing others is a substantial increase in dietary fibre intake. Box 29.2 lists foods with a high fibre content that can be eaten regularly with little effort or extra expense. Increasing the fibre content almost inevitably leads to reduced consumption of refined carbohydrates and saturated animal fats and lower total energy intake. Patients should introduce dietary fibre gradually because a sudden increase is likely to cause abdominal discomfort and distension and more flatus. Bulking agents (ispaghula husk preparations) can be taken in the early stages for a rapid result whilst avoiding unpleasant side-effects.

Clinical features of irritable bowel syndrome

Irritable bowel syndrome is a functional GI disorder characterised by abdominal pain and altered bowel habit without identifiable organic pathology. IBS can only be diagnosed clinically (after excluding organic causes) as there are no specific diagnostic tests. A group of experts formalised a diagnostic set of symptoms known as the Rome II Criteria. To fulfil a diagnosis of IBS, a patient must have the following symptoms continuously or recurrently for at least 3 months in a year: abdominal pain relieved by defaecation, and a change in stool frequency and consistency. Symptoms supporting the diagnosis include altered stool form, mucorrhoea and abdominal bloating.

The patient typically complains of episodic ‘cramping’ abdominal pain at any time of day and lasting from 15 minutes to several hours. The pain is unrelated to meals or other obvious provoking factors. It occurs anywhere in the abdomen but tends to arise peripherally, i.e. in either iliac fossa or epigastrium, and usually recurs in the same general area in any one patient.

Symptoms occur daily for weeks at a time and then resolve for weeks or months, only to return later. The patient may recognise that symptoms are worse at times of stress and are absent during weekends and holidays. The pain may provoke an urge to open the bowels, and evacuation may bring relief. An erratic bowel habit is characteristic of irritable bowel syndrome: passage of loose stools alternates with constipation, with small hard stools described as looking like rabbit pellets; but patients are divided into those for whom either diarrhoea or constipation is the predominant problem. Sufferers often complain of abdominal distension and excess flatus.

Pathophysiology and aetiology of irritable bowel syndrome

The pathophysiology is poorly understood. Colonic motility studies show abnormal rises in intraluminal pressure and disordered peristalsis with segmenting, non-propulsive contractions. The small volume of faeces (because of little residual fibre) becomes excessively dehydrated and fragmented. However, some patients with irritable bowel syndrome appear to be hypersensitive to gut distension and their symptoms may be made worse by a high-fibre diet. These in particular may benefit from a low-fibre diet plus methylcellulose fibre substitutes that do not ferment, e.g. Celevac. Thus the patient avoids constipation without the fermentation and excess gas production of a high-fibre diet. There is growing support for the view that at least some IBS is due to specific food intolerance, particularly wheat protein, and it is worth excluding this in a trial of treatment.

Management of irritable bowel syndrome

The diagnosis is made on the basis of a typical history and often after a trial of treatment. In the younger patient, where carcinoma is unlikely, abdominal and rectal examination (probably including flexible sigmoidoscopy) is all that is required. In IBS, these are normal except perhaps for mild tenderness in the area of pain. Other factors helping to exclude inflammatory bowel disease are a normal erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and an absence of weight loss, ill-health and tiredness, troublesome diarrhoea or rectal bleeding. In cases of diagnostic difficulty, small bowel radiology and other investigations can exclude Crohn’s disease.

Persistent upper gastrointestinal pain should be investigated, with gallstones or peptic ulcer disease in mind. In a patient over 50, irritable bowel syndrome is less likely, and cancer and diverticular disease must be excluded before IBS can be confirmed.