High or prolonged exposure to estrogens has been indicated to be one risk factor for breast cancer. 50 % of all estrogens are excreted in the bile and partly reabsorbed in enterohepatic circulation. By consuming whole grain bread it is possible to reduce the absorption of biliary estrogens and increase the fecal output of these hormones. Furthermore, whole-grain rye bread contains high amounts of lignans which have been shown to reduce breast cancer risk in rodents.
So far only one study has measured rye bread intake and a few studies have reported whole grain intake in relation to breast cancer risk the results not supporting risk lowering effects of whole grains. More information can be gathered from studies reporting fibre intake. In Case-control epidemiologic studies show that a high fibre diet reduces breast cancer risk. However, most prospective studies have not been able to show any fibre effects on risk. Only one prospective study has revealed that cereal fiber is protective in pre-menopausal subjects. On the other hand, in other study significant negative correlations have been found between fibre intake and breast cancer risk.
Rye has several possible mechanisms e.g. high lignan and fibre content, through which it could reduce the risk of breast cancer, but so far the evidence on the effects is still inadequate and more research on the subject is needed to confirm the relation.
Aubertin-Leheudre M, Gorbach S, Woods M, Dwyer JT, Goldin B, Adlercreutz H. (2008). Fat/fiber intakes and sex hormones in premenopausal American healthy women. J Steroid Biochem Molec Biol 112: 32-9.
Cade, JE, Burley VJ, Greenwood DC. (2007). The UK Women´s Cohort Study Screening Group. Dietary fibre and risk of breast cancer in the UK women´s Cohort Study. Int J Epidem 36: 431-438.
World Cancer Research Fund/American Institute for Cancer Research. (2007). Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective. Washington DC: AICR.
Mattisson I, Wirfält E, Johansson U, Gullberg B, Olsson H, Berglund G. (2004). Intakes of plant foods, fibre and fat and risk of breast cancer-a prospective study in the Malmö Diet and Cancer cohort. Br J Cancer 90: 122-127.
La Vecchia C, Chatenoud L. (1998). Fibres, whole-grain foods and breast and other cancers. Eur J Cancer Prev 7 (suppl 2): S25-28.
Adlercreutz H, Martin F (1980). Review. Biliary excretion and intestinal metabolism of progesterone and estrogens in man. J Steroid Biochem 13, 231-244.
Adlercreutz H. (2010) Can rye intake decrease risk of human breast cancer? Food Nutr Res 54:10.3402/fnr.v54i0.5231.
Egeberg R, Olsen A, Loft S, Christensen J, Johnsen NF, Overvad K, Tjonneland A. (2009) Intake of whole grain products and risk of breast cancer by hormone receptor status and histology among postmenopausal women. Int J Cancer 124:745-750.
Nicodemeus KK, Jacobs DR Jr, Folsom AR. (2001) Whole and refined grain intake and risk of incident postmenopausal breast cancer (United States). Cancer Causes Control 12(10):917-925.