Journal of the American College of Nutrition, Vol 5, Issue 5 443-450, Copyright © 1986 by American College of Nutrition
Metabolic effects of dietary versus parenteral fructose
C. B. Niewoehner
Fructose has been considered as an alternative sweetener to sucrose because
it results in less glycemia when given to normal subjects or to those with
mild noninsulin-dependent diabetes mellitus. Oral fructose also results in
efficient glycogen synthesis. However, multiple hepatotoxic effects have
been reported following parenteral fructose administration. We have
examined the effects of large oral fructose and glucose loads (4 g/kg) and
of graded intravenous fructose doses (50-500 mg/kg) on hepatic metabolism
and glycogen synthesis in normal, fasted rats. Fructose was absorbed more
slowly than glucose when given by gavage (59% vs 91% absorbed in 120 min).
Oral fructose administration resulted in greater liver and muscle glycogen
synthesis, despite smaller increases in plasma glucose and insulin
concentrations, than was found after oral glucose administration. Increases
in percent glycogen synthase I (active form) occurred after both oral
fructose and glucose loads (67% vs 115% increase). There was no evidence of
hepatotoxicity even after a very large oral fructose load. When small (less
than or equal to 125 mg/kg) iv doses of fructose were given, the portal
vein fructose concentration remained less than or equal to that found after
oral fructose administration (1.1 mM). The percent synthase I increased up
to threefold, and there was no evidence of hepatotoxicity. Larger iv doses
resulted in a fall in percent synthase I, an increase in percent
phosphorylase a, and inorganic phosphate and nucleotide depletion. We
conclude that the slow absorption of an oral fructose load prevents
hepatotoxic effects and permits efficient glycogen synthesis.
