C-13 APPEARANCE IN PLASMA-GLUCOSE AND BREATH CO2 DURING FEEDING WITH NATURALLY C-13-ENRICHED STARCHY FOOD IN NORMAL HUMANS

We have used a recently developed technique (isotope-ratio mass spectrometer) to measure C-13 appearance in plasma glucose and breath CO2 in eight normal subjects during feeding with naturally C-13-enriched starch. C-13 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. C-13 in plasma glucose displays a very different pattern from plasma glucose concentration. It increases steadily for 90 min before reaching a plateau for almost-equal-to 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 C-13 in plasma glucose during feeding with naturally C-13-labeled carbohydrates yields new insight in the study of carbohydrate bioavailability in humans.