Submitted to: Journal of Nutritional Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/1995
Publication Date: N/A
Interpretive Summary: It is important to know how one nutrient in the diet affects the absorption and utilization of another. For example, diets with high zinc have been shown in the past to reduce the absorption of copper into the body. However, recent work in our laboratory has shown that this effect is not consistent among diets offered to experimental animals. One of the diets that seems to prevent zinc from affecting copper status in adult rats is the new American Institute of Nutrition diet called AIN-93G. It differs from other diets in that it contains nutrients that might themselves affect copper status of an animal, such as the amino acid cystine and the ultratrace nutrient nickel, and thus, lessen the effects of zinc. We designed experiments to see if these dietary components were involved in preventing the zinc effect on copper status. The results showed that although the component cystine affected some indicators of copper status, it in itself was not the agent affecting the interaction between copper and zinc. Neither did the ultratrace element nutrient mix containing nickel have an effect on zinc-induced low copper status. However, the ultratrace element mix significantly stimulated growth when rats were fed a marginally copper-deficient diet but not when the rats were fed copper-adequate diets. So, it remains a mystery why the AIN-93G diet prevents a zinc effect on copper status and some other diets do not.
Technical Abstract: Although previous studies have shown that copper status of rats is compromised when they consume a diet with high zinc, studies using the new AIN-93G rodent diet did not show this effect. Because the new diet formulation contains components such as L-cystine and an ultratrace element mix that might affect copper metabolism, a study was done to determine if these components interfered with the effect of zinc. A 2 x 2 x 2 x 2 factorial study was designed with 2 dietary concentrations of copper, 3 and 9 mg/kg of diet; with L-cystine or DL-methionine; with or without the ultratrace element (UTE) mix; and with 2 concentrations of zinc, 35 and 350 mg/kg of diet. After 5 weeks, measures of copper status were made. Results showed that serum ceruloplasmin amine oxidase activity, a very sensitive copper status indicator, was not affected by feeding high zinc in the diet. Other status indicators such as serum copper or liver copper concentrations also were not affected by high-zinc feeding. It was concluded that the lack of an effect of high zinc on copper status when using the AIN-93G diet was not the result of using L- cystine or ultratrace elements in the diet. Other findings showed that dietary UTE stimulated growth in rats fed the marginal-copper diet but not in rats fed the high-copper diet. Rats fed diets containing DL-methionine had significantly higher concentrations of liver and intestinal copper that those fed diets with L-cystine.