Disorders of Large Bowel Motility, Structure and Perfusion

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 subjects of diet, and latterly, the colonic microbiome are respectable in surgical circles and have contributed to the understanding, prevention and management of many common diseases. Diseases, such as IBS, diverticular disease and appendicitis, common in Western society, appear to be far less common 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 patients with these disorders, and dietary changes are 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 (GI) 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, caused by a move to farming and by 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, sugars and fats, especially saturated animal fats and ‘trans’ fats in artificially hydrogenated vegetable oils (though these are gradually being phased out). Perhaps equally important, the modern diet contains far less absorbable and nonabsorbable 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 GI 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.