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Bean intake reduces inflammation
Inflammation is increasingly viewed as an important component in the etiology of chronic diseases including cancer, coronary heart disease and arthritis. The inflammatory response orchestrates host defenses to microbial infection and mediates tissue repair and regeneration, which may occur due to infectious or non-infectious tissue damage. Epidemiological evidence points to a connection between inflammation and a predisposition for the development of cancer, since long-term inflammation leads to the development of dysplasia. The results from epidemiologic studies suggest that nearly 15 percent of the worldwide cancer incidence is associated with microbial infection. Inflammation may contribute to the development of heart disease by making the inner lining of arteries swell, thereby narrowing the opening through which blood flows. In addition, inflammation may impair endothelial function. Elevated concentrations of soluble adhesion molecules—which are surrogate measures for endothelial dysfunction—and inflammatory biomarkers are closely associated with the incidence of atherosclerosis, insulin resistance and type 2 diabetes.
Recently, Iranian researchers evaluated the impact of diet on inflammatory status in 486 Tehrani female teachers aged 40 to 60 years [1]. A trained dietitian administered a validated semi-quantitative food frequency questionnaire for assessment of usual dietary intakes. Legume intake was calculated by summing up the consumption of beans including lentils, peas, chickpeas, and broad beans, and chickling vetch. The cutoffs for intake tertiles (g/wk) were <102, 102- ≤237 and ≥237. Inflammation was assessed by measuring levels of E-selectin, sICAM-1, sVCAM-1, hs-CRP, TNF, SAA, and IL-6.
Soluble cell adhesion molecules (sCAMs or cell surface binding proteins) are a class of cell adhesion molecules that may represent important biomarkers for inflammatory processes involving activation or damage to cells such as platelets and the endothelium. They include soluble forms of ICAM-1, VCAM-1, and E-selectin. High-sensitivity C-reactive protein is a protein found in the blood, that is synthesized in the liver and binds to phosphocholine expressed on the surface of dead or dying cells in order to activate the complement system via the C1Q complex. Tumor necrosis factor-α is a cytokine involved in systemic inflammation and is a member of a group of cytokines that stimulate the acute phase reaction. It is produced chiefly by activated macrophages, although it can be produced by other cell types as well. Serum amyloid A belongs to a family of apolipoproteins associated with high-density lipoprotein (HDL) in plasma, made by the liver that is secreted in response to inflammatory stimuli. And IL-6 is an interleukin that acts as both a pro-inflammatory and anti-inflammatory cytokine. It is secreted by T cells and macrophages to stimulate immune response, e.g. during infection and after trauma.
In this study, after controlling for potential confounders, individuals in the highest tertile of legume intake had lower serum concentrations of E-selectin (percent difference between the lowest and highest tertile: -14.1%; P = 0.04), soluble intercellular adhesion molecule-1 (-20.3%; P < 0.01), and soluble vascular cell adhesion molecule-1 (-15.6%; P = 0.01) compared with those in the lowest tertile. Legume intake was also inversely associated with serum concentrations of hs-CRP, TNF, and IL-6, even after controlling for potential confounders and dietary variables (percent difference between the lowest and highest tertile for hs-CRP: -39.2%, P < 0.001; for TNF: -15.9%, P = 0.04; and for IL-6: -39.5%, P < 0.01).
The authors of this study discussed the potential mechanisms through which legume consumption might affect adhesion molecules and inflammation. These include the low-glycemic index nature of legumes, and their high dietary fiber and phytochemical content. In regard to fiber, when the authors controlled for dietary fiber intake from non-legume sources, the associations with legumes were attenuated. This was also the case for magnesium intake. The authors concluded that if efforts could be made to increase the availability of leguminous foods, chronic disease risk could potentially be reduced.
Synopsis and implications of findings
Beans are low in total and saturated fat and high in protein and fiber. Those attributes alone make beans a healthful addition to the American diet. In addition, there is evidence that beans lower cholesterol [2]. In the current study, Iranian women age 40-60 years of age who were in the upper tertile of bean intake had lower levels of multiple indicators of inflammatory status. Since increased inflammation is thought to be involved in the etiology of coronary heart disease it is clear there are multiples ways in which legume consumption can decrease chronic disease risk. It is especially noteworthy that relative modest bean intake (≥40 g/week) was associated with such pronounced benefits.
Possible mechanisms by which beans reduce cancer risk
Epidemiological studies, such as the Nurses’ Health Study II and the Four-Corners Breast Cancer Study, have found intake of common beans and lentils to be associated with reduced breast cancer risk. Animal research has also shown significant inhibition of the post-initiation stage of chemically induced mammary carcinogenesis in the rat by the common bean. However, the means by which legume intake decreases cancer risk is unclear. In the current study, the impact of bean consumption on cell signal pathways was investigated as a means of identifying the mechanisms by which beans may reduce cancer risk [3]. At 21 days of age, female Sprague–Dawley rats were injected with 1-methyl-1-nitrosourea to induce mammary tumors. Seven days following carcinogen injection, all rats were randomized to diet groups on a percentage weight basis, 7.5, 15, 30 or 60% legume. Rats were fed their assigned diets ad libitum until the end of the study at 46 days post-carcinogen. In the highest bean intake group, carcinoma burden was reduced 62.2% (P < 0.001) and histological and western blot analyses revealed that the dominant cellular process associated with reduced burden was induction of apoptosis. Analysis of mammary carcinomas revealed changes in the phosphorylation states of mammalian target of rapamycin (mTOR) substrates (4E-binding protein 1 and p70S6 kinase) and mTOR regulators adenosine monophosphate-activated protein kinase and protein kinase B (Akt) (P < 0.001). mTOR is a serine/threonine protein kinase that regulates cell growth, cell proliferation, cell motility, cell survival, protein synthesis, and transcription. Effects on mTOR signaling in carcinomas were also found at lower dietary concentrations of beans (7.5-30% wt/wt). Plasma concentrations of insulin and insulin-like growth factor-1 were reduced by 36.3 and 38.9%, respectively, (P < 0.001), identifying a link to Akt regulation. Plasma C-reactive protein, a prognostic marker for long-term survival in breast cancer patients, was reduced by 23% (P < 0.001) in bean-fed rats. Identification of a role for the mTOR signaling network in the reduction of cancer burden by dietary bean is highly relevant given that this pathway is deregulated in the majority of human breast cancers.
Synopsis and implications of findings
Legumes are dietary staples in many parts of the world, providing a variety of nutrients including protein, potassium and B vitamins. However, bean intake in many Western countries is relatively low and below the recommended intake. The current study suggests that bean intake could inhibit the development of mammary cancer primarily by inducing apoptosis, or programmed cell death. Since even relatively low bean intake still induced favorable changes in cell signaling, the results suggest that even modest bean intake may help to reduce cancer risk.
1. Esmaillzadeh A, Azadbakht L. Legume Consumption Is Inversely Associated with Serum Concentrations of Adhesion Molecules and Inflammatory Biomarkers among Iranian Women. J Nutr. 2012; 142: 334-9.
2. Bazzano LA, Thompson AM, Tees MT, Nguyen CH, Winham DM. Non-soy legume consumption lowers cholesterol levels: A meta-analysis of randomized controlled trials. Nutr Metab Cardiovasc Dis. 2011; 21: 94-103.
3. Thompson MD, Mensack MM, Jiang W, Zhu Z, Lewis MR, McGinley JN, Brick MA, Thompson HJ. Cell signaling pathways associated with a reduction in mammary cancer burden by dietary common bean (Phaseolus vulgaris L.). Carcinogenesis. 2012; 33: 226-32.