Digestion of so-called resistant starch sources in the human small intestine

Abstract

Background: Resistant starch sources, which are only partially digested in the small intestine, can be used to increase colonic availability of short-chain fatty acids. Objective: To study the characteristics of the fermentation of resistant starch, the digestion of resistant starch in the small intestine has to be quantified. We compared the metabolic fates of highly digestible cornstarch (DCS), Hylon VII (type 2 resistant starch), and Novelose 330 (type 3 resistant starch), which are of corn origin and, therefore, naturally enriched in ¹³C. Design: After administration of 40 g starch or glucose to 7 healthy volunteers, glucose and exogenous glucose concentrations in serum and ¹³CO₂ excretion in breath were analyzed for 6 h. ¹³C abundance in carbon dioxide was analyzed by isotope ratio mass spectrometry (IRMS) and ¹³C abundance in glucose by gas chromatography–combustion IRMS. Results: By comparing the area under the curve (2 h) of exogenous glucose concentration in serum (¹³C glycemic index) after intake of starch or glucose, ¹³C glycemic indexes for DCS, Hylon VII, and Novelose 330 were calculated to be 82 ± 23%, 44 ± 16%, and 43 ± 15%, respectively. Comparison of 6-h cumulative percentage dose recovery in breath showed that 119 ± 28% of DCS, 55 ± 23% of Hylon VII, and 50 ± 26% of Novelose 330 was digested in the small intestine. Conclusion: The exogenous glucose response in serum and the ¹³CO₂ excretion in breath can be used to estimate small intestinal digestion of resistant starch, which amounts to ≈50%.