Beans & Cancer

Beans are a natural source of antioxidants and phytochemicals, and research shows that regular bean consumption may reduce the risk of certain types of cancer. Beans unique composition of fiber, as well as important micronutrients and antioxidants, makes them an important food choice for many reasons, including their possible anti-cancer properties for certain types of cancer, including colorectal, breast, and prostate.

COLORECTAL CANCER

Colorectal cancer (CRC) is cancer that starts in the color or rectum (the largest parts of the intestine). Despite the strong relationship between dietary habits and risk of CRC, and some suggestion of a protective effect, epidemiologic studies (studies that follow people over time to see if there are correlations between lifestyle and dietary habits and health outcomes) are generally insufficient to conclude that dry beans decrease CRC risk.

One cross-sectional study specifically related bean consumption to cancer mortality. Data compiled from 41 countries revealed that countries with the greatest consumption of beans had the lowest mortality ratesdue to colon cancer. (Correa, 1981) Nine case control studies have been conducted where legume intake on CRC risk was evaluated. Five case-control studies reported a protective effect of legume consumption on some aspect of CRC risk (Iscovich, 1992; Steinmetz, 1993; LeMarchand, 1997; Deneo-Pellegrini, 2002; Agurs-Collins, 2005), three reported no association (Lavecchia, 1988; Bidoli, 1992; Kampman, 1995), and one reported increased risk. (Haenszel, 1973) Another case-control study reported on fiber from pulses, rather than pulse intake and found a significant protective effect for individuals in the highest quartile of legume fiber intake. (Benito, 1991)

In a prospective study examining dietary patterns and disease risk as part of the Adventist Health Study, significant inverse associations between legume consumption—including beans, peas, and lentils—and colon cancer were found. (Singh, 1998) After 6 years of follow-up, the authors reported that overall, individuals consuming legumes > 2 times/week were 47% less likely of developing colon cancer when compared to individuals consuming legumes never to < 1 time/week.

Two studies have reported a protective effect of legumes against adenoma (tumor) recurrence. Lanza et al (2006) studied changes in specific subcategories of fruit and vegetable intake and risk of adenoma recurrence as part of the Polyp Prevention Trail in the United States. The authors reported a 65% reduced risk of advanced adenoma recurrence for subjects in the highest quartile of change in dry bean intake from baseline compared to individuals in the lowest quartile. There was no effect of change in bean intake on non-advanced adenoma recurrence. In a cohort of the Nurses Health Study, women consuming four or more servings of legumes per week had a 33% lower risk of adenoma recurrence than those consuming less than one serving/week. (Michels, 2006)

Three experimental studies have examined the relationship between dry bean consumption and chemically-induced colon cancer in rats. Hughes et al (1997) fed rats diets containing either pinto beans or casein as the protein source. They found that feeding pinto beans inhibited colon tumor incidence by 52% and significantly reduced the number of tumors that developed. In a similar study design, Hangen and Bennink (2002) also reported a protective effect of dry beans on experimental colon cancer. They found that feeding either black beans or navy beans to rats inhibited colon cancer by ~57%, and they also developed fewer tumors. In this study, the chemopreventive properties of beans was associated with significantly more resistant starch reaching the colon, resulting in higher colonic acetate and butyrate production, and a decrease in body fat.

In the last study, Rondini and Bennink (2012) also found that black beans inhibited chemically-induced tumors in rats. Black beans reduced the number of animals with colon tumors both early and late after carcinogen administration. Because the effect of beans on cancer development appeared to be due to a delay in the development of tumors from normal-appearing colonic mucosa, they further profiled gene changes in normal appearing colon tissue from black bean and casein-fed animals. They anticipated that the genes most important to black bean-induced suppression of tumor formation would have altered expression (increased or decreased) that paralleled tumor incidence. They identified 145 genes differentially expressed by beans compared to casein-fed animals. Bean-feeding induced changes in genes consistent with reduced cell proliferation and inflammation and enhanced energy metabolism.

These data provide preliminary evidence that including beans into the diet may affect molecular pathways in the colon that affect the development of cancer.

BREAST CANCER

Breast cancer is one of the most common cancers in the United States, and it is estimated that 1 in 8 U.S. women will develop invasive breast cancer over the course of her life. (Breast Cancer, 2015) Recognizing the risk factors and understanding the lifestyle choices that may reduce cancer risk is important and the research has continued to grow.

In the Nurses Health Study, Adebamowo et al (2005) found a significant inverse association with bean and lentil intake and risk of breast cancer. A statistically significant difference in relative risk was found comparing the average intake for highest bean and lentil eaters (2 or more times/week) to the lowest eaters (<1 time/month). However, utilizing the same cohort, Fung et al (2005) reported on dietary patterns and risk of postmenopausal breast cancer and found no association between legume intake (4-6 servings/week vs. < 1 serving/week) and risk of breast cancer.

Three case-control studies have examined bean intake in relation to risk of breast cancer. Silva et al (2002) conducted a case-control study on vegetarianism and risk of breast cancer in South Asian immigrants living in England. They reported significant, inverse associations between the highest (>107.4 g/day) and the lowest (<35 g/day) quartiles of pulse, lentil, and dhal (Indian dish made with lentils) consumption and risk of breast cancer in middle-aged women. A non-significant inverse association was also found for intake of non-starch polysaccharides from pulses when comparing highest (>2.6 g/day) to lowest (<0.9 g/day) quartile of intake. In a case-control study in China, Shannon et al (2005) found no association between non-soy legumes and breast cancer risk when comparing highest (> 3.9 servings/week) to lowest (<1.9 serving/week) quartile. The last case-control study, conducted in Argentina, found an increased risk in individuals consuming higher intakes of pulses. (Iscovich, 1989)

One study reported on fiber from beans, looking at food groups and micronutrient associations with risk of early-stage breast cancer in women in the U.S. (Potischman, 1999) They found an insignificant, inverse association between cases and controls for intake of fiber from beans when comparing the highest (>1.89g/day) to lowest quartile (<0.72 g/day) of intake.

Two ecological studies (studies looking at risk-modifying factors on health outcomes) found a negative association between legume consumption and breast cancer mortality (Armstrong, 1975 and Lagiou, 1999). In Correa et al’s cross-sectional study, they examined data from 15 countries looking at bean consumption and breast cancer mortality. (1981) Data revealed that countries with the greatest consumption of beans had the lowest breast cancer mortality rates.

PROSTATE CANCER

Prostate cancer is the second most common cancer in men in the United States (after skin) and is the second leading cause of death from cancer in men (National Cancer Institute, 2015). Prevention and early detection are key to reducing prostate cancer morbidity and mortality, and identify dietary approaches to reduce this risk is an important area of research.

One case-control and one cohort study specifically identified beans and a reduced risk of prostate cancer. The case-control study reported a reduced risk for prostate cancer with increasing consumption of baked beans (Key, 1997). An odds ratio of 0.844 (95% CI; 0.709 – 1.00) was determined per increase in serving of baked beans per week. A cohort study conducted in the Netherlands found an inverse relationship between consumption of broad beans and risk of prostate cancer. (Schuurman, 1998) Both studies reported that consuming beans reduced the risk of prostate cancer, but the results from the cohort study were not statistically significant.

Four studies compared the frequency of bean and lentil consumption to risk for prostate cancer. Mills and colleagues (1989) found that eating beans and lentils significantly reduced risk of prostate cancer. A meta-analysis of three case-control studies (Key, 1997; Villeneuve, 1999; Cohen, 2000) showed a statistically non-significant protective relationship between bean and lentil consumption and risk of prostate cancer odds ratio (OR) of 0.956. A cohort study did not report quantified data. but they did indicate that the association between prostate cancer mortality and bean and lentil consumption was not statistically significant. (Hsing, 1990) Finally, one case-control study reported a non-significant increase in prostate cancer was associated with eating beans, lentils, and peas. (Key, 1997)

Kolonel et al (2000) studied dietary patterns and risk of prostate cancer in the U.S. and Canada. When they differentiated between soy and non-soy legumes, an inverse relationship between non-soy legume (i.e. dry beans and lentils) consumption and prostate cancer was determined. Dry beans are the most commonly consumed non-soy legume in the U.S. and Canada, so this study suggests that eating beans may reduce risk of developing prostate cancer.

There were five case-control studies (Key, 1997; Kolonel, 2000; Lee, 1998; Jain, 1999; and Hodge, 2004) when the food category was broadened to include all pulses (dried beans, peas, chickpeas and lentils). Four ecological studies reported a protective effect of legume consumption on prostate cancer risk (Armstrong, 1975; Howell, 1974; Hebert, 1998; and Ganmaa, 2002). One cross-sectional study specifically examined bean consumption and mortality rates from prostate cancer. (Correa, 1981) Data from 15 countries revealed that countries with the greatest consumption of beans had the lowest death rates due to prostate cancer.

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