A new study has identified a mechanism of action by which the common dry bean (Phaseolus vulgaris L.) inhibits tumor growth in a rodent model of breast cancer. Consumption of dry beans has been reported to be associated with reduced cancer risk among people and reduced cancer burden in rodent models of cancer. In the study, the authors first conducted experiments using a high dietary concentration (60%) of beans in rats with carcinogen-induced mammary tumors.

The bean-fed rats developed significantly fewer and smaller mammary tumors than control rats who were not fed beans. The cellular process most associated with the reduced tumor burden was induction of apoptosis (programmed cell death). Additional analysis of mammary tumors revealed changes in the rapamycin (mTOR) pathway, which has been implicated in breast cancer. The authors also conducted experiments using lower dietary concentrations of bean (7.5% to 30%). Effects on mTOR signaling were also found at the lower dietary concentrations. In addition, circulating insulin and insulin-like growth factor-1 levels were reduced by 36.3 and 38.9%, respectively, in the bean-fed rats. Plasma C-reactive protein (CRP), a marker of inflammation, as well as a prognostic marker for long-term survival in breast cancer patients, was reduced by 23% in the bean-fed rats. The authors comment that identification of a role for the mTOR signaling network in association with bean-induced reduction of tumor burden is highly relevant, given that this pathway is deregulated in the majority of human breast cancers.

Comments regarding the study

Black beans, kidney beans, navy beans, pinto beans, pink beans, red beans and white beans are all dry beans (Phaseolus vulgaris L.). The following beans, some of which we do not recommend for breast cancer survivors, are not true dry beans: adzuki beans, black-eyed peas, chickpeas, fava beans, lentils, lima beans, and mung beans. The chemopreventive potential of dark beans such as black beans and navy beans appears to be greater than that of light-colored beans such as white beans due to the pigments in their seed coats. However, these pigments do not explain most of the anti-cancer effects of consuming dry beans.

Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.