Coupling of Zinc Dose to Frequency in a Regularly Recurrent Pattern Shows a Limited Capacity of Excessive Dietary Zinc to Compensate for a Previously Deficient Intake

Abstract

The impact of feeding a proportional dose of zinc in a regularly recurrent pattern (idiorrhythmic feeding) on body growth of weanling rats was studied to assess the extent to which an intake exceeding the requirement could compensate for a previously deficient intake. The idiorrhythmic regimen (I) was designed so that the overall dose-time equivalent (modulo; Mx) was kept constant over a selected period of time (epoch; E), whereas the actual dose and frequency varied regularly according to a predetermined pattern; that is, I = dnth(Mx)/dnth, where Mx and dnth are the selected dose-time equivalent and the sequential number of zinc-dosing days, respectively. For example, 3 mg Zn·kg-1 diet fed every day (I = 3/1) and 24 mg Zn·kg-1 diet fed 1 d in an 8-d period (7 d of feeding a zinc-deficient diet) (I = 24/8) are dose-time equivalents because they both provide 72 mg Zn·kg-1 over a 24-d E. Modulos of M3, M6, M12 and M24 were used, which provided 3, 6, 12 and 24 mg Zn·kg-1·d-1 dose-time equivalents during a 24-d E. Each modulo had seven analogous idiorrhythms: I = Mx/1, 2Mx/2, 3Mx/3, 4Mx/4, 5Mx/5, 6Mx/6 and 8Mx/8; for example, with 8 Mx/8, 24, 48, 96 or 192 mg Zn·kg-1 diet was fed every 8th d; on the other 7 d a diet without a zinc supplement was fed for M3, M6, M12 and M24, respectively. Zinc dose-rate idiorrhythm generated a complex, gestalt-like, biphasic growth response pattern where an intake of dietary zinc exceeding requirements had either no effect (M3 or average of 3 mg kg-1 diet) or fully compensated for only 1 (M6 and M12 or average of 6 and 12 mg Zn·kg-1 diet) or 2 (M24 or average of 24 mg Zn·kg-1 diet) d.