Use of pulmonary hydrogen (H2) measurements to quantitate carbohydrate absorption

Abstract

A technique was developed to quantitate the absorption of ingested carbohydrate by means of continuous measurements of pulmonary H₂ excretion. This technique is based on the observation that H₂ is produced in the colon when carbohydrate is fermented by colonic bacteria, and this H₂ is then excreted by the lungs. The quantitative relationship of pulmonary H₂ excretion to unabsorbed carbohydrate was studied in nine subjects. After ingestion of 6.5, 13, and 26 g of lactulose (a nonabsorbable disaccharide), H₂ excretion increased linearly, averaging (±1 SEM) 13±3.5, 23±7.2, and 49±7 ml per 2 hr. Because of consistent individual differences in H₂ excretion per gram of lactulose, the variability of this linear response was less in a given subject, with the H₂ excretion after 6.5 g and 26 g lactulose dosages averaging 55±4.2% and 214±16% of that observed after the 13 g dose. It was further demonstrated with fecal homogenates, as well as in rats after direct intracecal instillation of carbohydrate, that there was no significant difference in the rate of H₂ formation from lactulose as compared with the normally ingested sugars. Thus, a subject's H₂ excretion after a 13 g dose of lactulose can be used as a standard to convert H₂ excretion after ingestion of other carbohydrates into grams of carbohydrate not absorbed. Application of this technique to seven partially gastrectomized patients indicated all subjects malabsorbed a portion of a 100 g dose of glucose whereas six of seven completely absorbed a 25 g dose. Malabsorption of physiologic quantities of various carbohydrates was clearly demonstrated in one subject. This technique appears to provide quantitative information on carbohydrate malabsorption not readily obtained by presently available techniques.