Reduced food consumption is a major manifestation of zinc (Zn) deficiency. Many manifestations of Zn deficiency are complications of anorexia nervosa and bulimia nervosa. We evaluated serum and 24-hour urinary Zn values in 12 healthy volunteers and 33 eating disorder patients before and after hospitalization which included either Zn supplementation (75 mg Zn/day) or placebo. Bulimics had depressed serum Zn concentrations (p<0.025). Admission urinary Zn was lower in bulimics (258 +/−44 micrograms/day), and significantly depressed in anorexics (196 +/−36 micrograms/day, p<0.005) vs controls (376 +/−45 micrograms/day). During hospitalization, serum Zn concentrations increased in all supplemented patients vs no change with placebo. Urinary Zn excretion increased in supplemented bulimics (p<0.001) and placebo (p<0.05). Urinary Zn excretion markedly increased in supplemented anorexics (179 +/−65 to 1052 +/−242 micrograms/day); however, placebo values fell or remained unacceptably low (admission 208 +/−48 micrograms/day; discharge 160 +/−17 micrograms/day). By dietary history, controls consumed the Recommended Dietary Allowance (RDA) for Zn (11.95 +/−1.25 mg/day); anorexics 6.46 +/−1.14 mg/day; and bulimics 8.93 +/−1.29 mg/day. We suggest that Zn deficiency may act as a“sustaining”factor for abnormal eating behavior in certain eating disorder patients.