Galactose is one of the monosaccharides of importance in human nutrition. It is converted to glucose-1-phosphate in the liver and subsequently stored as glycogen, or is converted to glucose and released into the circulation. The increase in plasma glucose is known to be modest following galactose ingestion. Whether this is due to a small increase in hepatic glucose output, or to a relatively large increase in hepatic glucose output but a concomitant increase in glucose disposal, is not known in humans. Therefore, the rates of glucose appearance (Ra) and disappearance (Rd) were determined over an 8-hour period in normal subjects using an isotope dilution technique. The subjects ingested 50 g galactose or water alone in random order at 8 AM on separate occasions. Plasma glucose, glucagon, lactate, urea nitrogen, total amino acids, and uric acid and serum insulin and triglycerides also were determined. Following galactose ingestion, there was a modest transient increase in peripheral glucose and insulin concentrations. This was associated with a modest increase in the glucose Ra. The calculated amount of glucose appearing in the circulation as a result of galactose ingestion was 9.8 g, while the amount of glucose disappearing over the 8 hours was 9.9 g. Thus, following ingestion of 50 g galactose by overnight-fasted men, approximately 20% appears as additional glucose in the circulation. Data obtained in animals suggest that a large amount of the galactose is stored as glucose in glycogen. Nevertheless, the conversion of galactose to glucose in the liver may have been greater than suggested by the increase in glucose appearance in the circulation due to substitution for other gluconeogenic substrates.
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From the Metabolic Research Laboratory and Section of Endocrinology, Metabolism, and Nutrition, Veterans Affairs Medical Center, Minneapolis; and the Departments of Medicine, and Food Science and Nutrition, University of Minnesota, Minneapolis, MN. Submitted February 14, 2000; accepted June 9, 2000. Supported by Merit Review funds from the Department of Veterans Affairs. Address reprint requests to M.C. Gannon, PhD, Director, Metabolic Research Laboratory (111G), VA Medical Center, One Veterans Drive, Minneapolis, MN 55417. Copyright © 2001 by W.B. Saunders Company 0026-0495/01/5001-0009$10.00/0 doi:10.1053/meta.2001.19442