Fecal hydrogen production and consumption measurements - Response to daily lactose ingestion by lactose maldigesters

The alteration of hydrogen (H-2) metabolism, which accounts for the large decrease in breath H-2 excretion following prolonged ingestion of malabsorbed carbohydrate (lactulose, lactose in lactose maldigesters) was studied in six lactose-maldigesting adults. Metabolic inhibitors of the three main H-2-consuming reactions (methanogenesis, sulfate reduction, and acetogenesis) were used to independently measure H-2 production and consumption in fecal samples obtained after 10 days of either dextrose or lactose feeding. Absolute fecal H-2 production (net of production minus consumption) after 3 hr of incubation with lactose was approximately threefold lower after lactose adaptation (242 +/- 54 mu l) compared to dextrose adaptation (680 +/- 79 mu l, P = 0.006). Fecal H-2 consumption was not affected by either feeding period. We conclude that decreased absolute H-2 production, rather than increased H-2 consumption, is responsible for the decrease in breath H-2 observed with lactose feeding.