A model to produce pure zinc deficiency in rats and its use to demonstrate that dietary phytate increases the excretion of endogenous zinc.

An early effect of zinc deficiency in rats is loss of appetite with consequent malnourishment. To obviate the need for pair-feeding, rats were fed liquid semipurified diets by gastric tube feeding. Rats tube fed a zinc-deficient diet at a daily rate of 90-110 g/kg thrived for 6-7 days and then rapidly became seriously ill. In contrast rats fed the deficient diet ad libitum stopped growing after 3 days but remained relatively healthy. Animals tube fed a zinc-replete diet or the deficient diet with subcutaneous injections of zinc grew normally and suffered no ill effects. Rats tube fed the deficient diet and supplemented parenterally with zinc excreted significantly more endogenous zinc into small intestinal luminal washings and into feces than unsupplemented rats. Sodium phytate, added to the tube feed in three groups of rats fed the deficient diet and supplemented daily with 0, 0.33 and 3.3 mg Zn/kg, significantly increased the zinc content of luminal washings in all three groups, increased fecal zinc excretion in two groups and lowered body zinc levels, estimated by femur zinc, in two groups. Tube feeding provides a means to study: 1) pure zinc deficiency without malnourishment of other nutrients; and 2) the excretion of endogenous zinc into the gastrointestinal tract.