Trypsin Inhibitor Activity and Tannin Content Do Not Affect Calcium Bioavailability of Three Commonly Consumed Legumes

Calcium bioavailability from legumes containing a range in trypsin inhibitor activity (TIA) and tannin concentration was studied. Three cultivars (Phaseolus vulgaris) were hydroponically grown and intrinsically labeled with ^4SCa. Raw and cooked legumes were fed to six groups of 6-wk old male Sprague-Dawley rats. Another group received an intraperitoneal (IP) injection of ⁴⁵Ca. An eighth group was fed a casein metal extrinsically labeled with ⁴⁵Ca. The absorption of calcium from legumes by rats averaged 47.1 ± 7.5% of IP dose. Average phytate content of the legumes was 1.7% and oxalate 0.37%. Raw legumes had an average of 15000 TIA units/g of whole bean, which were completely removed by cooking. Calcium absorption was unaffected by TIA or tannin content. Reduced availability of bean calcium was likely due to phytate and/or oxalate present in legumes.