Consumption of black beans and navy beans (Phaseolus vulgaris) reduced azoxymethane-induced colon cancer in rats.

Beans (Phaseolus vulgaris) are an important food staple in many traditional diets. There is limited evidence to suggest an inverse relationship between bean consumption and colon cancer. The objective of this study was to determine whether consumption of black beans and/or navy beans would reduce colon carcinogenesis in rats. Rats were fed a modified AIN-93G diet (control) or diets containing 75% black beans or 75% navy beans for 4 wk, and then colon cancer was initiated by administration of two injections of azoxymethane 1 wk apart. At 31 wk after the second injection, the incidence of colon adenocarcinomas was significantly lower (P < 0.05) in rats fed the black bean (9%) and navy bean (14%) diets than in rats fed the control diet (36%). Total tumor multiplicity was also significantly lower in rats fed the black bean (1.1) and navy bean (1.0) diets than in rats fed the control diet (2.2). The 44-75% reduction in colon carcinogenesis in rats fed beans was attributed to 1) more controlled appetites, leading to significantly less body fat, and 2) much greater concentrations of butyrate in the distal colon. It was concluded that eating black beans and navy beans significantly lowered colon cancer incidence and multiplicity.