Carbohydrate malabsorption and intestinal gas production

Virtually all patients complaining of excessive flatulence have high concentrations of H₂ in their flatus. H₂ is produced by certain strains of colonic bacteria during the fermentation of malabsorbed carbohydrates. Other colonic bacteria utilize H₂, and the H₂ available for excretion represents the net of production and consumption. These two processes show marked individual variability. Studies using breath H₂ as an indicator of carbohydrate malabsorption have shown that a variety of carbohydrates are malabsorbed by normal subjects, including leguminous vegetables, lactose and most of the commonly ingested flours with the exception of rice flour. Excessive flatulence appears to occur when large quantities of carbohydrates are delivered to the large intestine of subjects whose flora is particularly adept at producing gas. The treatment of flatulence usually requires dietary measures to reduce the quantity of carbohydrate reaching the colon, i.e. a low lactose, low wheat diet.