The human requirement for copper. I. Healthy men fed conventional, American diets

Each of 13 men was fed diets made from conventional foods for two to seven periods lasting 30 days in a metabolic ward. There was a total of 47 experimental periods. Supplementation of the basal diet with each of several bran or other fiber sources was done in no particular order; each subject was fed the unsupplemented diet for at least one period. The diet was designed to contain amounts of essential nutrients close to the Recommended Dietary Allowances; it resembled the "average" American diet as it contained 16% protein, 40% fat, and 44% carbohydrate. Only minimal variation in energy intake and physical activity of the men was permitted; body weight remained constant within +/- 2%. Copper in food, feces, and urine was measured during the last 12 days of each period. Linear regression of balance (intake minus the sum of fecal and urinary losses) revealed a daily requirement of 1.30 mg (95% confidence limits of 1.24 to 1.35 mg). On consideration of a calculated surface loss of 0.25 mg/day, the requirement is 1.55 mg/day. The requirement was unaffected by the type of fiber source. A review of published data revealed that this requirement substantially exceeds the amount of copper found in many conventional diets.