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Colonic Microbiota, Nutrition and Health. Edited by G R Gibson, M B Roberfroid (Pp 304; illustrated; £93) The Netherlands: Kluwer Academic Publishers, 1999. ISBN 0412798808.
I was taught as a medical student that the major function of the colon was that of a storage organ. Since then, premises about the colon have evolved and the complexities of colon function is much better understood, as described by Gibson and Roberfroid's multi-authored book Colonic Microbiota, Nutrition and Health.
Although the authors state that the purpose of the book is to overview current knowledge of the activities and functions of the gut microflora, the scope goes beyond these boundaries and takes us on an ecological journey into the exciting life of gut microflora and their impact on colon function in health and disease, and the intimate critical relationship between diet, bacteria, and quality of life.
Gastroenterologists are still recovering from the impact that a bacterium, Helicobacter pylori, has had on upper gastrointestinal tract pathology. In this context, it is interesting to note that the large bowel is the most heavily colonised part of the gastrointestinal tract yielding up to 1012bacteria per gram of intestinal contents in healthy human subjects. It is a complex ecosystem in which the numerous and different species of bacteria degrade and ferment substrates that have escaped digestion in the small bowel. Major genera include bacteroides, bifidobacteria, lactobacilli, clostridia, and enterobacteria, and the main products of bacterial fermentation of the substrate that reaches the colon are short chain fatty acids (SCFA) and gases including hydrogen, carbon dioxide, and, in some individuals, methane. The relevance of SCFA, is that they act as a source of energy for intestinal mucosal cells and reduce the pH of colonic contents. One particular SCFA, butyrate, may be important in protecting against colorectal cancer. The relevance of fermentation to human metabolism can be gauged from the fact that the energy equivalent of 15–40 g of carbohydrate is metabolised by the large bowel.
The book outlines the technological revolution that has occurred in understanding the natural microbial world. Molecular biology has invaded gut microbiology, with the limitations of enrichment cultural techniques being integrated into techniques based upon the detection of the genomic DNA or the analysis of rRNA.
A fascinating aspect of the book that concerns and affects all of us are the chapters on food. With the craze of low carbohydrate diets in order to counter obesity that are sweeping the US, it is refreshing to realise the importance of carbohydrates and the concept of functional food. These foods target specific functions in the body in a positive way due to the presence of health enhancing ingredients. Colonic foods are an example of such functional foods that target the large intestine. These are foods that contain an ingredient that does not undergo significant modification during transit through the small intestine, but reach the colon where they are utilised by the resident bacteria producing metabolites that influence the physiological and biochemical processes in a beneficial manner. Dietary fibre is the best known of the “colonic foods” and is divided into soluble and insoluble fibre. Soluble fibers include pectin, guar gum, B glucan, and psyllium and result in modest reductions in blood lipids, affecting the total and LDL cholesterol fractions. Insoluble fibres (cellulose and lignin) are mainly responsible for faecal bulking. Dietary fibre may play a protective role in diverticular disease and colorectal cancer. Other functional foods are the fructans and resistant starch which, in animal models, affect the triglyceride rich fractions. A novel and potentially important approach to prevention and therapy of colonic diseases is the concept of prebiotics and probiotics. The probiotic approach involves adding live microorganisms to the gastrointestinal tract while prebiotics enhance certain components of the existing flora. Probiotics have potential in the prevention and treatment of rotavirus infections, lactose malabsorption, and food allergy. Tentative claims for benefits of prebiotics include reduction in obesity, improved control of non-insulin dependent diabetes, reduction in the risk of atherosclerotic cardiovascular disease, and prophylaxis of acute gastroenteritis.
How does the above affect individuals? It seems that we should include the following foods in our diet: garlic, onions, asparagus, chicory, dandelion, artichokes, soy beans, leeks, Jerusalem artichokes, wheat, bananas, and rye. Quite a tall order!
The authors have made an important contribution to the concept of the local and systemic effects of the colon, and outlined the benefits of a healthy colon and the evolvement of the idea that functional foods have prophylactic and therapeutic properties. A minor criticism is that there is a repetition of ideas in certain chapters. I would highly recommend this excellent work for gastroenterologists as a seminal study. Gastroenterologists, primary care physicians, and nutritionists will find this book a useful guide, but it will also provide a basic understanding for all health workers.