CuN subjects In order to be enrolled into the CuN control arm, subjects who have had RYGB surgery will be recruited and screened for eligibility (inclusion and exclusion criteria below). Subjects will have plasma copper concentrations in the normal range (80 - 155 μg/dL for women and 70 - 140 µg/dL for men, and/or ceruloplasmin activity above 62 units/L-1). Subjects will also be eligible if they can be matched for stage of weight management (either active weight loss or weight stable) and gender with a CuD subject. Subjects will be notified about their copper status and their eligibility and their willingness to participate in the study will be determined.