SUMMARY In this paper aspects of the variability of methane producing status have been examined, and a survey of breath methane excretion in various clinical and control populations is reported. Prevalences of methane excretion were 54% in healthy controls, 53% in non-gastrointestinal patients and 32% in gastrointestinal patients. Patients with Crohn's disease, ulcerative colitis, and pneumatosis cystoides intestinalis had significantly lower prevalences of methane excretion (13%, 15%, and 11% respectively). Faecal constituents and in vitro incubation analysis were similar in breath methane excretors and non-excretors. Several patients did not excrete methane in the breath although methane was present in colonic gas. The results indicate that different gastrointestinal patient groups have different prevalences of breath methane excretion and that all healthy subjects may produce methane but only when the production reaches a threshold does it appear in the breath.Methane and hydrogen are produced during anaerobic bacterial activity in the large intestine and are excreted in flatus and expired breath. Human intestinal tract fermentation produces hydrogen, but methane is neither a universal constituent of colonic gas nor of expired breath.1 2

The gas above liquid cultures of a variety of human intestinal anaerobic bacteria was sampled and analysed by headspace gas chromatography. Hydrogen production was greatest with strains of the genus Clostridium, intermediate with anaerobic cocci and least with Bacteroides sp. Very few strains produced methane although small amounts were detected with one strain of B. thetaiotaomicron, C. perfringens and C. histolyticum. There may be a relationship between these anaerobic bacteria and several gastrointestinal disorders in which there is a build up of hydrogen or methane in the intestines.

1. Gum arabic (GA) is a water-soluble polysaccharide (molecular weight approximately 850000) containing 2. The metabolism of GA has been studied in the rat. Adult male Wistar rats were given GA incorpornted 3. Intestinal contents were examined for precipitable GA using acidified ethanol. GA was found from stomach 4. Caecal excision and restoration of intestinal continuity resulted in G A recovery from stomach to rectum. 5. Excreted methane, hydrogen and volatile fatty acids (VFA) were measured as indicators of bacterial activity in the caecum and colon. Methane excretion increased on the OBfGA diet and H, concentrations remained unaltered. The Elem diet abolished gas production. When the animals were given the Elem+GA diet, H, and methane were only produced after 28 d. Faecal VFA increased with increasing GA intake, acetate concentration increased and butyrate concentration decreased with increasing GA dosage. Significant decreases in concentrations of VFA were found from caecum to left colon and from left colon to faeces.6 . It can be concluded that GA degradation occurs in the caecum and is associated with increased methane excretion, increased VFA concentrations and changes in the proportions of various VFA in the faeces. rhamnose, arabinose, glucuronic acid and galactose.into either an Oxoid breeders (OB) diet or an elemental (Elem) diet.to small intestine but not in the caecum, colon or rectum.

In a population study the concentration of methane in the expired breath of methane-producing subjects was significantly related to the dietary intake of noncellulosic polysaccharide pentose (p less than 0.01) and to the intake of lignin (p less than 0.05). The single dose administration of complex polysaccharide sources rich in pentoses to fasting subjects did not result in an increase in methane production when measured over 5 h. The single dose administration of D(+) xylose and L(+) arabinose led to a significant increase in methane excretion in methane producers.

1. The influence of three diets ((1) high-fibre -low-fat, (2) low-fibre -high-fat, (3) commercial breeding diet) on the concentration of short chain fatty acids (SCFA) has been investigated in male and female rats up to 14 weeks of age.2. Hydrogen was detected in respired gas in all rats with no significant differences between diets or sex. Methane was detected only in control-fed rats at 12 weeks of age and thereafter. Caecal contents contained higher concentrations of SCFA than were found in faeces. There were no significant differences in the total faecal SCFA excreted by rats on the three diets. The proportions of SCFA in the caecum and faeces were influenced by diet.3. The production and excretion of hydrogen, methane and SCFA in the rat appeared to reflect different aspects of bacterial metabolism. Comparison of caecal and faecal SCFA may indicate differential absorption from the colon or differential metabolism by bacteria or colonic mucosa which may be influenced by diet.