The objective of the present study was to investigate the postprandial metabolism of two starches with contrasting rates of hydrolysis in vitro. Characterized using the Englyst method of in vitro starch classification, C*Set 06 598 contained predominantly rapidly digestible starch and C*Gel 04 201 contained predominantly slowly digestible starch. Each test starch, naturally enriched with 13C, was fed to ten healthy female volunteers as part of a moderate fat test meal (containing 75 g test starch and 21 g fat), in a double-blind randomized crossover design. The metabolic response to each starch was measured after an overnight fast, in an acute 6 h study, before and after 14 d of daily consumption of 75 g test starch. During each acute study, blood samples were taken at 15 min intervals for the first 2 h and at 30 min intervals for the remaining 4 h. Breath 13CO2 enrichment was measured at the same time points and indirect calorimetry was performed for 20 min every 40 min immediately before and throughout the study. Significantly more rapid, greater changes in postprandial plasma glucose, NEFA and serum insulin concentrations were observed after consumption of the rapidly digestible starch. Breath 13CO2 output over the first 3-4 h rose rapidly then began to decline following consumption of the rapidly digestible starch, but plateaued for the slowly digestible starch. The 14 d adaptation period did not affect any of the glycaemic or lipaemic variables but there was a reduction in postprandial plasminogen activator inhibitor-1 concentrations. These data confirm that starches characterized as predominantly rapidly digestible versus slowly digestible by the Englyst procedure provoke distinctly different patterns of metabolism postprandially.