Fecal Hydrogen Production and Consumption Measurements (Response to Daily Lactose Ingestion by Lactose Maldigesters)

The alteration of hydrogen (H₂)metabolism, which accounts for the large decrease inbreath H₂ excretion following prolongedingestion of malabsorbed carbohydrate (lactulose,lactose in lactose maldigesters) was studied in six lactose-maldigesting adults.Metabolic inhibitors of the three mainH₂-consuming reactions (methanogenesis,sulfate reduction, and acetogenesis) were used toindependently measure H production and consumption in fecal samples obtained after10 days of either dextrose or lactose feeding. Absolutefecal H₂ production (net of production minusconsumption) after 3 hr of incubation with lactose was approximately threefold lower after lactoseadaptation (242 ± 54 l) compared to dextroseadaptation (680 ± 79 l, P = 0.006). FecalH₂ consumption was not affected by eitherfeeding period. We conclude that decreased absolute H₂ production,rather than increased H₂ consumption, isresponsible for the decrease in breath H₂observed with lactose feeding.