Absorption, endogenous excretion, and balance of zinc in growing rats on diets with various sugars replacing starch.

The effect of partially replacing starch for various sugars on the apparent and true absorption, endogenous excretion, and balance of zinc was investigated in a study with growing rats. Six groups of five or six animals with an initial live weight of 39.4 +/- 2.7 g were fed diets that had the same Zn content (22 mg/kg), but differed in the sugar content: 1. Starch only (56%); 2. Glucose (15%); 3. Fructose (15%); 4. Sucrose (30%); 5. Galactose (15%); and 6. Lactose (30%). At the start of a 15-d fecal and urinary collection period, each animal was given an intramuscular injection of 380 kBq 65Zn for estimating endogenous Zn excretion by isotope dilution. The ratio of the specific activity of fecal Zn (after 12 d) to that of urinary Zn (after 9 d) was applied to reflect the ratio of endogenous to total fecal Zn collected from day 10 to 15. This ratio averaged 0.59, without significant differences among treatments. For this period, apparent and true absorption averaged 87.1 and 94.7% of Zn intake, respectively, and did not significantly differ among diets. Urinary excretion of 65Zn and of stable zinc by the galactose-fed rats was markedly higher than that by the other animals. Their Zn balance was, per unit weight gain, comparable with that of the other groups (30.7 vs 28.2 to 30.2 micrograms/g).