Measurements of pulmonary excretion of methane (CH4) were used to obtain information on the CH4-producing bacteria in man. Preliminary studies indicated that (a) all CH4 excreted by man is produced by colonic bacteria, (b) there is no appreciable utilization of CH4 by man, and (c) breath CH4 can serve as a relatively accurate indicator of CH4 production in the intestine.

The rate of pulmonary CH4 excretion varied enormously, ranging from undetectable (<5 x 10–6 ml/min) to 0.66 ml/minute. In general, the CH4 excretion rate for subjects was consistently very low (nonproducers) or relatively large (producers). 33.6% of the adult population were producers of CH4. Whereas diet, age over 10 yr, and sex did not influence the rate of CH4 production, some familial factor appeared to play an important role. 84% of siblings of CH4 producers also were producers, while only 18% of the siblings of nonproducers were found to be CH4 producers. This familial tendency appeared to be determined by early environmental rather than genetic factors.

These studies of CH4 excretion demonstrate that the exposure of individuals to intestinal bacterial metabolites may differ markedly and that these differences may be chronic and determined by familial factors.

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