Dietary Cooked Navy Beans and Their Fractions Attenuate Colon Carcinogenesis in Azoxymethane-Induced Ob/Ob Mice

Abstract

Based on the protective effects of cooked dry bean consumption in a human intervention study, we evaluated which fraction of cooked dry beans is responsible for its cancer-preventive effects. Cooked navy beans (whole beans), the insoluble fraction (bean residue) or soluble fraction of the 60% (vol:vol) ethanol extract of cooked navy beans (bean extract), or a modified AIN-93G diet (16.6% fat including 12.9% lard) as control diet were fed to 160 male obese ob/ob mice after 2 azoxymethane injections. In comparison to control-fed mice, dysplasia, adenomas, or adenocarcinomas were detected in fewer mice on either bean fraction diet (percent reduction from control: whole beans 54%, P = 0.10; bean residue 81%, P = 0.003; bean extract 91%, P = 0.007), and any type of colon lesions, including focal hyperplasia, were found in fewer mice on each of the 3 bean diets percent reduction from control: whole bean 56%, P = 0.04; bean residue 67%, P = 0.01; bean extract 87%, P = 0.0003. These results suggest that both the soluble and the insoluble fraction of the extract contribute to the cancer-protective effect of cooked navy beans.

ACKNOWLEDGMENTS

G. Bobe and K. G. Barrett contributed equally to the work. We thank the Michigan Bean Commission for the donation of navy beans. This research was supported financially in part by the Intramural Research Program of the National Institute of Health and National Cancer Institute and in part by a grant from the United States Agency for International Development through the Bean/Cowpea Collaborative Research Support Program (CRSP) and by the Michigan Agricultural Experiment Station.

Notes

^a Composition of 740 g whole navy beans and navy bean residue was 144 g fiber, 168 g protein, and estimated to be 243 g starch, 11 g fat, and 29 g total sugar (46). The bean residue diet was formulated to be equal to the whole bean diet in everything except for having lower concentrations of phenolics and oligosaccharides.

^b The bean extract diet was formulated to be equal to the whole bean diet except for having higher concentrations of phenolics and oligosaccharides.

^c Composition of AIN 93-MX mineral mix and AIN 93-VX vitamin as described in Reeves et al. (47).

^a 40 mice were assigned to each diet. Starting at Day 131 on the experimental diets, a total of 9 mice (control: 0; whole bean: 6; bean residue: 2; bean extract: 1) died spontaneously.

^b Within each column, incidences followed by different subscript letters differ significantly at P < 0.05. We observed only in the control group multiple lesions of the same type within 1 mouse (11 hyperplastic sites in 9 mice, 5 dysplastic sites in 4 mice, and 5 adenocarcinomas in 4 mice).