Pathways for glucose disposal after meal ingestion in humans.

To characterize postprandial glucose disposal more completely, we used the tritiated water technique, a triple-isotope approach (intravenous [3-H(3)]glucose and [(14)C]bicarbonate and oral [6,6-(2)H(2)]glucose) and indirect calorimetry to assess splanchnic and peripheral glucose disposal, direct and indirect glucose storage, oxidative and nonoxidative glycolysis, and the glucose entering plasma via gluconeogenesis after ingestion of a meal in 11 normal volunteers. During a 6-h postprandial period, a total of approximately 98 g of glucose were disposed of. This was more than the glucose contained in the meal ( approximately 78 g) due to persistent endogenous glucose release ( approximately 21 g): splanchnic tissues initially took up approximately 23 g, and an additional approximately 75 g were removed from the systemic circulation. Direct glucose storage accounted for approximately 32 g and glycolysis for approximately 66 g (oxidative approximately 43 g and nonoxidative approximately 23 g). About 11 g of glucose appeared in plasma as a result of gluconeogenesis. If these carbons were wholly from glucose undergoing glycolysis, only approximately 12 g would be available for indirect pathway glycogen formation. Our results thus indicate that glycolysis is the main initial postprandial fate of glucose, accounting for approximately 66% of overall disposal; oxidation and storage each account for approximately 45%. The majority of glycogen is formed via the direct pathway ( approximately 73%).