Pulmonary hydrogen and methane excretion following ingestion of an unabsorbable carbohydrate: a study of twins.

Pulmonary excretion of hydrogen and methane after administration of an unabsorbable disaccharide (lactulose) was determined in 228 adult Hungarian twins, 60 monozygous (MZ) and 54 dizygous (DZ) pairs. More than 98% of the subjects (224 of 228) excreted large amounts of hydrogen between 90 and 180 min after lactulose administration. Methane excretion in the fasting state was observed in 124 of 228 of the probands (54.4%), and 68 of 228 (29.8%) produced additional methane in response to lactulose ingestion. In contrast to hydrogen production, both methane excretion and production were significantly more frequent in females than in males. In the total group, and more distinctly in females, the correlation between peak hydrogen and methane concentrations was negative. Twin concordance of fasting methane excretion and lactulose-induced methane production was near 70% in both MZ and DZ pairs. Heritability estimates of methane excretion and production based on intrapair correlation and variance were smaller than unity, and intrapair correlation coefficients were larger in twin pairs living apart than in those living in the same household. Methane excretion is comparatively frequent in the Hungarian population, and a substantial proportion of fasting methane excreters (55%) produce additional methane from lactulose. The sex difference of methane excretion appears to be characteristic of European populations. The twin data disprove regular Mendelian inheritance of methane production and are suggestive of genetic effects in a multifactorial system.