Homeostatic control of zinc metabolism in men: zinc excretion and balance in men fed diets low in zinc.

Zinc metabolism was studied in 11 men. The study began with 28-d equilibration when dietary zinc was 159 mumol/d (X), followed by 35-d periods when the diet contained 21.9 (I), 37.5 (II), 51.6 (III), or 67.8 (IV) mumol Zn/d in random order, and ended with 35 d with X. The diet was conventional foods and egg white protein. Zinc balance, including surface and semen losses, was zero only during I. Semen zinc was unaffected by diet. Plasma zinc dropped to 0.44 and 0.49 mumol/L in two subjects during I and was significantly decreased during I compared with X (P < 0.0002). Urinary zinc declined with decreasing zinc intake. A combination of urinary and plasma zinc criteria from Baer and King (Am J Clin Nutr 1984; 39:556-70) could be used to distinguish stages of zinc deficiency. By these criteria, no subjects were deficient during IV, one was marginally deficient during III, three were marginally deficient during II, and seven were deficient during I.