13C appearance in plasma glucose and breath CO2 during feeding with naturally 13C-enriched starchy food in normal humans.

We have used a recently developed technique (isotope-ratio mass spectrometer) to measure 13C appearance in plasma glucose and breath CO2 in eight normal subjects during feeding with naturally 13C-enriched starch. 13C in CO2 and plasma glucose, metabolites and insulin concentrations, carbohydrates, and lipid oxidation were measured after ingestion of 76 g glucose equivalent of crackers, pasta, or polenta. 13C in plasma glucose displays a very different pattern from plasma glucose concentration. It increases steadily for 90 min before reaching a plateau for approximately 2 h and slowly declines during the last 2 h of the study. No significant difference was observed with the three different starchy foods tested although plasma glucose tended to be higher during feeding with polenta. In summary measurement of 13C in plasma glucose during feeding with naturally 13C-labeled carbohydrates yields new insight in the study of carbohydrate bioavailability in humans.