Zinc and nitrogen balance in adolescent females fed varying levels of zinc and soy protein

Abstract

Zinc and nitrogen balances were determined in 14 girls, 12.5 to 14.5 years of age, during a 30-day period. Diets were composed of ordinary foods and supplied 100% of the Recommended Daily Allowance for protein. The lunch menus were typical of those served in School Lunch Programs except that milk was omitted and calcium supplements were added. The dietary variables were the levels of zinc and the amount of defatted soy which replaced the meat in noon meals. The diets were: S₀Z_13.4 (13.4 mg zinc and no soy); S₃₀Z_13.4 (13.4 mg zinc and 30% of meat replaced by soy); and S₃₀Z_7.4 (7.4 mg zinc and 30% of meat replaced by soy). Subjects fed 7.4 mg zinc daily lost significantly (P < 0.01) less zinc in their feces than the subjects fed the higher level of zinc during the 18-day collection period. Partial substitution of soy for meat in lunch menus did not affect fecal or urinary zinc or nitrogen losses. Mean retentions of zinc by subjects fed Diets S₀Z_13.4, S₃₀Z_13.4 and S₃₀Z_7.4 were +0.53, +0.42 and ~~0.32 mg/day, respectively. Nitrogen retention was not significantly affected by zinc intake. However, nitrogen and zinc retentions were significantly correlated (r = 0.416, P < 0.015).