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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Pinto Beans Are a Source of Highly Bioavailable Copper in Rats¹

USDA, Agricultural Research Service, Grand Forks Human Nutrition Research Center, Grand Forks, ND 58202

^* To whom correspondence should be addressed. E-mail: preeves{at}gfhnrc.ars.usda.gov.

The trace element copper (Cu) is a required nutrient in the diets of humans. It has been found in animal studies to be essential for efficient iron absorption and oxygen utilization and for aiding free-radical degradation. Dry beans (Phaseolis vulgaris) are potentially good sources of Cu; thus, the objective of this study was to determine the bioavailability of Cu from dry beans using the pinto bean as the source. Dry beans were obtained from a local market, cooked according to package directions, and dried. Weanling male Sprague-Dawley rats (8 groups of 8 rats each) were fed a Cu-deficient diet (AIN-93G) for 4 wk followed by 2 wk of Cu repletion with diets containing 0–6.5 mg Cu/kg diet added as CuSO₄ or with 0.6 and 1.5 mg Cu/kg incorporated into rat diets as pinto beans at 10 and 20%. Standard response curves were developed based on repletion-induced recovery of 10 indices of Cu status, including organ Cu concentrations and Cu-dependent enzyme activities, in response to increasing dietary Cu as CuSO₄. Recovery of these variables in rats fed the pinto bean diets was compared with the standard response curve at similar levels of dietary Cu. Based on the recovery of all 10 variables, the relative bioavailability of Cu from dry beans was at least 100% of that with the highly available CuSO₄. For 3 of the variables, liver and heart Cu concentrations and serum superoxide dismutase 3 activity, estimated bioavailability values of Cu from beans were 138, 140, and 134%, respectively, of those from CuSO₄. We conclude that the dry pinto bean is a good source of dietary Cu with respect to both concentration and bioavailability.