Copper is an essential nutrient for humans and is cofactor in enzymes that participate in critical body functions. Insufficient copper can lead to hematological and neurological abnormalities that may be irreversible if left untreated. Copper deficiency is believed to be rare in the U.S. population because typical dietary intake is usually sufficient to meet requirements. More recent evidence suggests that specific populations may be susceptible to copper deficiency in cases where copper absorption in the gut is impaired following gastric surgery or in individuals with high intakes of zinc. Preliminary studies by us and others have identified significant levels of moderate and severe symptomatic copper deficiency in patients who have undergone weight loss (bariatric) gastric bypass surgery. Copper deficiency in humans is difficult to recognize and treat because current diagnostic tools rely on measures of plasma concentrations of copper and ceruloplasmin, which are neither sensitive nor specific for copper deficiency, and early warning blood markers (biomarkers) have not been identified. Recent developments indicate that copper chaperone molecules and cuproenzymes such as cytochrome C oxidase and superoxide dismutase may be more sensitive to changes in copper status, but there has been very little work done in humans. The studies outlined here are aimed at assessing copper status using these biomarkers in gastric bypass surgery patients who are at risk for symptomatic copper deficiency. In addition, patients identified to be deficient will be supplemented with copper and this treatment will be evaluated using biomarker concentrations. The findings of these studies should provide insight into the effectiveness of novel biomarkers to identify those at risk and to guide appropriate treatment to prevent serious and permanent morbidity due to copper deficiency.