Publications & Bibliography
|
Our Main Topics
International Programs
Nutrition Portal
|
|
 |
THE LARGE INTESTINE IN NUTRITION AND DISEASE
Under the responsability of Dr. John Hedley Cummings
SUMARY OF THE MONOGRAPH
The classical view of the human colon is that of an organ which absorbs salt and water and provides a mechanism for the orderly disposal of waste products of digestion. It is now clear, however, that it has a major role in digestion through the salvage of energy, and possibly nitrogen, from carbohydrate and protein not digested in the upper gut. This is achieved by the metabolism of anaerobic bacteria and is known as fermentation.
The principal dietary substrates for fermentation in man are starch, non-starch polysaccharides (NSP) which are the major plant cell wall carbohydrates, oligosaccharides and some sugars. These are broken down to short-chain fatty acids (SCFA) (acetate, propionate and butyrate), the gases H2 and CO2 and stimulate bacterial growth, or biomass. SCFA are rapidly absorbed, acetate reaches muscle where it serves as a fuel for the tissues, whilst propionate is largely cleared by the liver and may contribute to the regulation of lipid metabolism. Butyrate is metabolised by the colonic epithelium, which derives 60-70% of its energy from bacterial fermentation products. Butyrate is an important regulator of cell growth and differentiation.
Hydrogen disposal in the colon is either by excretion through the lung or in flatus, or through further metabolism to methane, sulphide and acetate.
Stimulation of biomass leads to increased faecal bulk and bacterial protein synthesis.
The principal chronic colonic diseases, constipation, cancer, diverticular disease and ulcerative colitis, are also affected by fermentation and its products. Bowel habit is partly determined by the amount of carbohydrate reaching the colon, whilst in ulcerative colitis there is evidence for sulphur compounds and other bacterial end-products affecting cell metabolism.
Over the last decade, much progress has been made in our understanding of the pathology and molecular genetics of colon carcinogenesis. This has culminated in the development of a well-defined model for the aetiology of colon cancer. It has been proposed that the pathology of malignant tumours in the colon frequently (though not exclusively) follows a series of events known as the adenoma-carcinoma sequence. Certain genetic alterations are known to occur frequently in colonic adenocarcinomas. Fermentation in the large bowel is now understood to be a protective factor in colon cancer. The role of butyrate on colonic cells at the molecular level provides an exciting link between dietary factors and the development of colon cancer. Whilst the fermentation of NSP (fibre) undoubtedly generates butyrate, in vitro studies have shown that the fermentation of starch generates greater proportions of butyrate than the fermentation of other carbohydrates. Resistant starch may therefore be a significant dietary factor in colon cancer.
The recommendation for countries with Western-style diets to increase their intake of starch and NSP has become universal since it was first suggested by the US Senate Select Committee on Nutrition and Human Needs in 1977 — the McGovern Report. Limits for starch intake have usually been set by default, that is starch is considered to be an energy filler in the diet once limits have been set for fat and protein.
The specific advantages of consuming starch are that as a substitute for saturated fat it will lower blood cholesterol, substituting for sugar will reduce the risk of dental caries and, together with resistant starch, may contribute to the prevention of bowel cancer. Moreover, many starchy foods such as cereals, pulses and vegetables contain a wide variety of micronutrients which sugary and fatty foods do not.
A number of national bodies have now made quantitative recommendations for increases in "dietary fibre" intake but, because of the lack of an agreed definition of fibre and of a method for measuring it, these recommendations do not cross international boundaries very well.
Therefore, the BNF, WHO and the UK Department of Health have opted for NSP as the best index of fibre. However theevidence points to the goal of a diet characterised by high NSP (and starch) intakes.
Language: english
Edited by the Danone Institute of Belgium
Published in 1996
155 pages
To download the entire monograph,, click here.
For more information about this initiative, you can contact the Danone Institute of Belgium.
|
|
Our Network
|
