White beans provide more bioavailable iron than red beans: studies in poultry (Gallus gallus) and an in vitro digestion/Caco-2 model.

Iron-biofortification of crops is a strategy that alleviates iron deficiency. The common bean (Phaseolus vulgaris L.) is an attractive candidate for biofortification. However, beans are high in polyphenols that may inhibit iron absorption. In vitro studies have shown that iron bioavailability from white beans is higher than that from colored beans. In this study, our objective was to determine if white beans contain more bioavailable iron than red beans and to determine if the in vitro observations of bean-iron bioavailability would be evident in an in vivo feeding trial. We compared iron bioavailability between diets containing either white (Matterhorn) or red (Merlot) beans, which differ in polyphenol content. One-week-old chicks (Gallus gallus) were divided into four groups: 1. "WB": 40% white-bean diet; 2. "RB" :40% red-bean diet; 3. "WB+Fe": 40% white-bean diet; 4. "RB+Fe": 40% red-bean diet (51, 47, 179, and 175 ppm iron, respectively). Diets 1 and 2 had no supplemental iron; whereas 125 µg/g iron was added to diets 3 and 4. For 8 weeks, hemoglobin, feed consumption, and body weights were measured. Divalent metal transporter 1 (iron-uptake-transporter), duodenal-cytochrome-B (iron reductase), and ferroportin (iron-exporter) expressions were higher (p<0.05), villus-surface-area (tissue iron-deficiency adaptation) was greater in the "RB" group vs. other groups. Cecal microflora was similar between treatments. Hemoglobin, body-hemoglobin iron, and body weights were lower in the "RB" group vs. other groups (p<0.05). In vitro analysis showed lower ferritin formation (less bioavailable iron) in cells exposed to the "RB" diet. We conclude that the in vivo results support the in vitro observations; i. e., white beans contain more bioavailable iron than red beans.