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 13 C. Design: After administration of 40 g starch or glucose to 7 healthy volunteers, glucose and exogenous glucose concentrations in serum and 13 CO 2 excretion in breath were analyzed for 6 h.13 C abundance in carbon dioxide was analyzed by isotope ratio mass spectrometry (IRMS) and 13 C abundance in glucose by gas chromatography-combustion IRMS. Results: By comparing the area under the curve (2 h) of exogenous glucose concentration in serum ( 13 C glycemic index) after intake of starch or glucose, 13 C 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 13 CO 2 excretion in breath can be used to estimate small intestinal digestion of resistant starch, which amounts to Ϸ50%.Am J Clin Nutr 2000;72:432-8.

To diagnose hypolactasia, determination of lactase enzyme activity in small intestinal biopsy material is considered to be the golden standard. Because of its strongly invasive character and the sampling problems, alternative methods have been looked for. We analysed the 13C-glucose response in serum after consumption of 25 g of naturally enriched 13C-lactose. As an internal standard, 0.5 g of 2H-glucose was added and the 2H-glucose response in serum was measured simultaneously. The studies were performed in healthy volunteers with a background of genetically determined lactase nonpersistence (n = 12; low lactase activity) and lactase persistence (n = 27; high lactase activity). The results were compared with those of the lactose hydrogen breath test, the lactose 13CO2 breath test and the previously described 13C-lactose digestion test. After consumption of 13C-lactose and 2H-glucose, the mean ratio 13C-glucose/2H-glucose concentration in serum at 45-75 min was 0.26 +/- 0.09 in the low lactase activity group and 0.93 +/- 0.17 in the high lactase activity group (P < 0.01). Threshold of the ratio between digesters and maldigesters was calculated as 0.46. Accuracy of the new test was superior to all other tests. We conclude that the 13C/2H-glucose test has the potential of determining the small intestinal lactase activity in vivo and of estimating the amount of lactose which is digested in the small intestine.

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