CIRCADIAN PATTERNS OF TOTAL 24-H HYDROGEN AND METHANE EXCRETION IN HUMANS INGESTING NONSTARCH POLYSACCHARIDE (NSP) DIETS AND THE IMPLICATIONS FOR INDIRECT CALORIMETRIC AND D-2 O-18 METHODOLOGIES

Objectives: To quantify the relationship between substrate fermentatio n and total 24-h H-2 and CH4 excretion on mixed diets and to assess er rors incurred In the calculation of energy expenditure and fuel select ion by the exclusion of these gases from standard calculations. Design and subjects: Twelve healthy lean men were studied over two consecuti ve dietary periods oi 3 weeks. Measurements of total H-2 and CH4 excre tion were made during 24 h within a whole body calorimeter. Subjects w ere fed a diet containing 16g or 38g of nonstarch polysaccharide (NSP) and 16g or 19g resistant starch (RS). Colonic fermentation was measur ed by balance techniques during the two dietary treatments. Results: T here was an inverse non-linear relationship between H-2 and CH4 excret ion on both diets (r(2) = 0.53; P < 0.001), but absolute excretion did not increase significantly as the intake of NSP and RS (from 28 +/- 3 and 45 +/- 4 g/day) increased. No relationship was round between dayt ime and 24-h measurements of H-2 and CH2. H-2 and CH4 excretion introd uces an error of less than 0.2% and 1% in calculations of energy expen diture and CO2 production from the standard human equations used in in direct calorimetric (IC) and doubly labelled water (DLW) methodologies respectively, and less than 2% in fuel utilisation calculated as % no n-protein energy expenditure from IC. Conclusions: This study provides evidence that neither daytime nor total 24-h rates of H-2, or CH4 exc retion accurately predict degree nf fermentation of NSP + RS in either Individual subjects or groups of subjects, probably because of change s in the stochiometry of the fermentation process.