Circadian patterns of total 24-h hydrogen and methane excretion in humans ingesting nonstarch polysaccharide (NSP) diets and the implications for indirect calorimetric and D2 18O methodologies

OBJECTIVES: To quantify the relationship between substrate fermentation and total 24-h H2 and CH4 excretion on mixed diets and to assess errors incurred in the calculation of energy expenditure and fuel selection by the exclusion of these gases from standard calculations. DESIGN AND SUBJECTS: Twelve healthy, lean men were studied over two consecutive dietary periods of 3 weeks. Measurements of total H2 and CH4 excretion were made during 24h within a whole body calorimeter. Subjects were fed a diet containing 16 g or 38 g of nonstarch polysaccharide (NSP) and 16 g or 19 g resistant starch (RS). Colonic fermentation was measured by balance techniques during the two dietary treatments. RESULTS: There was an inverse non-linear relationship between H2 and CH4 excretion on both diets (r2 = 0.53; P < 0.001), but absolute excretion did not increase significantly as the intake of NSP and RS (from 28 +/- 3 and 48 +/- 4 g/day) increased. No relationship was found between daytime and 24-h measurements of H2 and CH4. H2 and CH4 excretion introduces an error of less than 0.2% and 1% in calculations of energy expenditure and CO2 production from the standard human equations used in indirect calorimetric (IC) and doubly labelled water (DLW) methodologies respectively, and less than 2% in fuel utilisation calculated as % non-protein energy expenditure from IC. CONCLUSIONS: This study provides evidence that neither daytime nor total 24-h rates of H2 or CH4 excretion accurately predict degree of fermentation of NSP+RS in either individual subjects or groups of subjects, probably because of changes in the stochiometry of the fermentation process.