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Title: A study of breath methane excretion
Author: McKay, Linda F.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1981
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Anaerobic bacterial metabolism in the colon produces hydrogen, methane, volatile fatty acids and carbon dioxide. Hydrogen and methane are excreted in flatus and the expired breath. Investigations in this Thesis attempted to identify factors which may influence methane excretion in man and explain why all subjects do not excrete methane. The proportions of methane producing subjects in two healthy populations studied in Edinburgh were 33% and 70% respectively. Age and sex did not significantly alter methane excretion. Dietary intakes, faecal components and bowel function were found to be similar in methane producing and non-methane producing subjects. An association was found between the ingestion of the pentose fraction of non-cellulosic polysaccharides and the concentration of breath methane in methane producing subjects. This association may be the result of a steady metabolic state in the caecum. Ingestion of pentose monomers D(+) xylose and L(+) arabinose increased methane excretion, in methane producing subjects, over five hours of study. The lack of gas production following acute complex polysaccharide administration could be due to a relatively slow metabolic response of colonic bacteria. Production of methane following the acute administration of free pentoses and the absence of methane production after the ingestion of polysaccharide sources may indicate that the release and availability of free pentose monomers from plant polysaccharides may be rate limiting steps in this process. Patient groups with clinically defined diseases appeared to have altered prevalences of methane production compared to control populations. In healthy populations there is great variation in the proportion of methane producers and the concentrations excreted. It is therefore unlikely that the methane status of an individual could be used as a diagnostic aid. Results of methane status may only be significant in population studies. The inaccessability of the human caecum necessitates the use of animal models and in vitro bacterial cultures. Caecectomy and the feeding of an elemental diet to intact rats abolished methanogenesis. A gum arabic supplemented control diet increased methanogenesis whereas methane excretion remained absent when gum arabic was added to the elemental diet. Methanogenic bacteria appear to colonise the caecum and require a fibrous residue or matrix for colonisation and as a substrate. Small but significant amounts of methane were produced by Clostridium histolryticum, C. perfrincens and C. septicum in pure culture. Simple in vitro experiments with the addition of various substrates to the growth medium of two control methanogens, Methanobrevibacter ruminantium and Methanosarcina barkeri, and C. histolyticum gave a confusing pattern of results, however L(+) arabinose increased gas production from each of the bacteria. Human methane production may result from the metabolism of other gastrointestinal organisms such as Clostridia.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available