DIETARY ZINC SUPPLEMENTS DO NOT ENHANCE CATCH-UP GROWTH OF RATS DURING RECOVERY FROM PROTEIN-ZINC MALNUTRITION WHEN THE DIETS ARE BASED ON EITHER ISOLATED SOYBEAN PROTEIN OR CASEIN

Young male rats were fed a low-protein (LP) diet (3% albumin) with 9 ug Zn/g diet for 21 d which halted the growth process. Relative to baseline values (d 0), the LP diet resulted in decreases of 19%, 47%, and 13% in serum albumin, serum zinc, and tibia zinc, respectively. Control rats were fed a balanced diet containing 15% albumin and 12 ug Zn/g for the same 21 d. The major objective of the study was to determine the efficacy of dietary zinc at and above the normal requirement (12 ug/g) to support catch-up growth after severe malnutrition. Following the 21 d LP or C periods, rats were fed for another 21 d with diets containing either 20% isolated soybean protein or 20% casein and supplemented with 1 of 3 levels of zinc ranging from 12 ug/g to 45 ug/g; a 2x2x3 factorial design was used. The rats recovering from protein malnutrition gained weight faster than the controls, but after 21 d the catch-up growth was still incomplete. Soybean protein, compared to casein, significantly depressed recovery of body weight, body length, and serum albumin. Dietary zinc supplementation of 36 ug/g was sufficient to replete both serum and tibia zinc but did not significantly improve catch-up growth in any of the tissues measured.