Diet and Cancer
Promising New Research on Soy and Breast Cancer
A recent study from Johns Hopkins School of Medicine suggests that soy foods like Silk® Soymilk may help modestly reduce breast cancer risk, but further research is needed.
Scientists have been investigating soy foods' possible role in reducing breast cancer risk for more than 15 years. Many indicators have suggested that soy may help contribute to breast cancer protection. For instance, in Japan—where soy foods are prominent—breast cancer is only about half as common as it is in the U.S.(1) However, it is important to note that establishing a direct link between cancer risk and diet, especially specific foods, is difficult.
In the recent Johns Hopkins investigation, researchers gathered and analyzed data from 18 previous studies. Their findings indicate that women consuming higher quantities of soy were 14% less likely to develop breast cancer than women who consumed relatively little soy. However, these results were not universal to all women. Furthermore, since women who consume soy foods may be more likely to maintain an overall healthy diet and lifestyle, their apparent reduced cancer risk cannot necessarily be attributed solely to soy.
While some evidence, including this latest study, suggests that soy foods like Silk Soymilk may modestly reduce breast cancer risk, no solid conclusions can be made at this time. Nevertheless, professionals agree that because of their many known benefits, soy foods are an excellent choice for a healthy diet and lifestyle.
Understanding Cancer
Approximately 10 million Americans today are cancer survivors, with close to one and a half million new diagnoses of cancer each year in the United States.(2) According to the National Institutes of Health, medical costs for cancer are approximately $190 billion per year.
Throughout the world, cancer rates differ greatly. For example, prostate cancer occurs 50 times more frequently in Uganda than in China, and women in Denmark are three times more likely to develop breast cancer than those in Japan.(2) Rates in the United States for these cancers fall somewhere in the middle.
Much of the difference in cancer rates can be explained by lifestyle, including diet. In fact, approximately one-third of cancer deaths are thought to be related to lifestyle factors. In contrast, genetics are not a very important factor in cancer risk.(3) When people move from one country to another, it generally takes only one or two generations before cancer rates among family members are the same as those in long-time residents of their adopted homeland.(4)(5)
The cancer process starts with damage to DNA, the genetic material of the cell, which results in a mutation—or a change in the way the DNA instructs the body to make new cells. This can result in chaotic, uncontrolled growth of abnormal cells. As these cells multiply, they can form a large mass called a tumor and begin to spread to other parts of the body, a process call metastasis. Tumors that invade a vital organ can gradually prevent that organ from performing its function. Unfortunately, it can take years before the cancer grows to a point where it can be detected by medical tests.
Diet Affects Cancer Risk
Diet and other lifestyle factors can affect the cancer process even at the earliest stages. For example, smoking, excessive sun exposure and alcohol can all lead to mutations in DNA. On the other hand, compounds in some foods, especially fruits and vegetables and also soy products, can help repair damaged DNA, reducing the risk of abnormal cell growth.
Even after cancer cells begin to multiply, some food components may slow or reduce tumor growth. Compounds in citrus not only stimulate enzymes that help repair DNA damage (6), but also inhibit tumor growth.(7) A compound in grapes and wine called resveratrol has similar effects.(8) And substances in soy products such as tofu and soy milk have been shown in animals to slow the growth of a variety of tumors and inhibit metastasis.(9)(10)
Strategies for Reducing Cancer Risk
Diet has been studied most extensively in relation to colon, breast and prostate cancers. Leading health organizations suggest the following dietary and lifestyle strategies for reducing your risk for cancer:
- Limit intake of fat, especially saturated fats from animal sources. High-fat diets have been linked in many studies to increased risk for different cancers such as cancer of the prostate (11) and endometrium (the lining of the uterus).(12)
- Eat plenty of fruits and vegetables. These foods are sources of many potentially beneficial compounds, including antioxidants that have been shown to inhibit the cancer process.
- Eat a diet high in fiber. It’s not clear whether fiber itself reduces cancer risk, or whether those who eat high-fiber meals just happen to also reap the benefits of a diet that is rich in whole plant foods and low in animal products. But either way, there is evidence that populations consuming a diet based on fiber-rich foods such as whole grains, beans, fruits, vegetables and nuts, are at lower risk for cancer.
- Reduce alcohol intake. Even moderate drinking may increase cancer risk, especially for cancer of the breast and esophagus.(13)
- Stay active. Physical exercise may help reduce risk for some cancers.(14)(15)
- Avoid Smoking and exposure to second-hand smoke.
- Use sunscreen when outdoors.
Soy Foods and Cancer Risk
Although it is easiest to identify overall eating patterns that affect cancer risk, research suggests that certain individual foods have unique properties that may reduce risk. For example, tomatoes contain an antioxidant called lycopene that may help protect against prostate cancer. A group of vegetables that includes broccoli, cabbage and Brussels sprouts contains compounds that are linked to a lower risk for colon cancer.
Soybeans and the foods made from them may play a unique role in reducing risk for some cancers. They are the only commonly-consumed foods that provide significant amounts of isoflavones, compounds that have been studied for more than 15 years for their proposed anticancer effects.(9) There is particular interest in the role of soy foods and isoflavones in reducing risk of breast and prostate cancer.
Soy Foods and Breast Cancer
Soy isoflavones may be one of the reasons that women in Japan have lower rates of breast cancer than Western women. A recent analysis of 12 population studies found that soy food intake was associated with a modest reduction in the risk of breast cancer.(16) But the most exciting findings are those showing that consuming soy foods early in life—in childhood and adolescence—may dramatically reduce breast cancer risk later in life.(16-18) This isn’t surprising, since there is growing evidence that early life factors such as birth weight, the age at which a girl begins to menstruate, and most importantly, the age at first pregnancy, are related to later breast cancer risk.(20)
In one study, Chinese women who had consumed at least 11 grams of soy protein (the amount in about 1 1/2 cups of soy milk) per day in their early teen years were 50% less likely to develop breast cancer compared to Chinese women who consumed little soy during adolescence.(17) Similarly, in a study of Asian Americans, lifelong consumption of soy foods was associated with a one-third reduction in breast cancer risk, whereas soy food consumption during adulthood did not affect cancer risk.(18) These studies suggest that that just one to two servings of soy foods per day in early adolescence is protective.
Soy Foods and Prostate Cancer
Men in Japan are just as likely as American men to develop prostate tumors, but they are far less likely to die of prostate cancer. This is because their small tumors—referred to as latent prostate cancer—rarely progress to the more advanced life-threatening disease.(21)(22) This is likely due to several factors, but according to the International Prostate Health Council, eating soy foods may be one.(23)
In animal studies, both isoflavone-rich soy protein and isolated isoflavones significantly inhibit the development of prostate tumors.(24) And in laboratory studies, adding isoflavones to prostate cancer cells makes the cells much more susceptible to radiation treatments.(25) That is, radiation more effectively destroys cancer cells when isoflavones are added to the mix. Furthermore, one study in China found that men who consumed the most soy were about half as likely to have prostate cancer as men who consumed the least.(26)
However, only clinical trials—studies in which subjects are actually fed soy—can form the basis for definitive conclusions about soy’s possible role in cancer protection. While there have been only a few of these studies, the results from one of them are especially interesting: In this small study of men who had been unsuccessfully treated for prostate cancer, consuming soy isoflavones favorably affected serum prostate specific antigen (PSA).(27) PSA, which is a protein produced by the prostate, is an indicator of prostate cancer risk. The men consumed 120 milligrams per day of isoflavones, which is the amount found in about four to five servings of soy.
Silk and a Healthy Diet
No single food or dietary pattern can guarantee protection against cancer. But following a diet that includes plenty of fruits and vegetables and is rich in other whole plant foods is an essential part of a healthy lifestyle. Products like Silk Soymilk can make a big difference. Including more Silk in your diet can help reduce your intake of animal fats while providing high-quality protein. And when you make Silk a part of your daily routines, you are assured of getting plenty of readily-absorbable calcium.(28) In addition, soy foods like Silk Soymilk are the best natural sources of isoflavones, compounds with a number of proposed cancer-fighting properties.
1. American Cancer Society. Cancer Facts and Figures 2006. Atlanta: American Cancer Society; 2006, p. 35
2. Society AC. Cancer Facts and Figures. 2005.
3. McCredie M. What have we learned from studies of migrants. Cancer Causes Control 1998;9:1-2.
4. Shimizu H, Ross RK, Bernstein L, Yatani R, Henderson BE, Mack TM. Cancers of the prostate and breast among Japanese and white immigrants in Los Angeles County. Br J Cancer 1991;63:963-6.
5. Ziegler RG HR, Pike MC, Hildesheim A, Nomura AM, West DW, Wu-Williams AH, Kolonel LN, Horn-Ross PL, Rosenthal JF, Hyer MB. Migration patterns and breast cancer risk in Asian-American women. J Natl Cancer Inst 1993;85:1819-1827.
6. Gao K HS, Niu Y, et al. The citrus flavonoid naringenin stimulates DNA repair in prostate cancer
cells. J Nutr Biochem 2006;17:89-95.
7. Poulose SM HE, Patil BS. Citrus limonoids induce apoptosis in human neuroblastoma cells and have radical scavenging activity. J Nutr 2005;135:870-877.
8. Lee SC, Chan J, Clement MV, Pervaiz S. Functional proteomics of resveratrol-induced colon cancer cell apoptosis: Caspase-6-mediated cleavage of lamin A is a major signaling loop. Proteomics 2006;6:2386-2394.
9. Sarkar FH, Li Y. Soy isoflavones and cancer prevention. Cancer Invest 2003;21:744-57.
10. Zhou JR, Yu L, Zhong Y, Blackburn GL. Soy phytochemicals and tea bioactive components
synergistically inhibit androgen-sensitive human prostate tumors in mice. J Nutr 2003;133:516-21.
11. Fleshner N, Bagnell PS, Klotz L, Venkateswaran V. Dietary fat and prostate cancer. J Urol
2004;171:S19-24.
12. Littman AJ, Beresford SA, White E. The association of dietary fat and plant foods with endometrial cancer (United States). Cancer Causes Control 2001;12:691-702.
13. Boffetta P, Hashibe M. Alcohol and cancer. Lancet Oncol 2006;7:149-56.
14. Torti DC, Matheson GO. Exercise and prostate cancer. Sports Med 2004;34:363-9.
15. Bernstein L, Patel AV, Ursin G, et al. Lifetime recreational exercise activity and breast cancer risk among black women and white women. J Natl Cancer Inst 2005;97:1671-9.
16. Trock BJ H-CL, Clarke R. Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst 2006;98:459-471.
17. Shu XO, Jin F, Dai Q, et al. Soyfood Intake during Adolescence and Subsequent Risk of Breast Cancer among Chinese Women. Cancer Epidemiol Biomarkers Prev 2001;10:483-8.
18. Wu AH, Wan P, Hankin J, Tseng CC, Yu MC, Pike MC. Adolescent and adult soy intake and risk of breast cancer in Asian-Americans. Carcinogenesis 2002;23:1491-6.
19. Korde L FT, Wu A, et al. Adolescent and childhood soy intake and breast cancer risk in Asian-American women. Breast Cancer Res Treat 2005;88:S149.
20. Russo J, Mailo D, Hu YF, Balogh G, Sheriff F, Russo IH. Breast differentiation and its implication in cancer prevention. Clin Cancer Res 2005;11:931s-6s.
21. Yatani R, Kusano I, Shiraishi T, Hayashi T, Stemmermann GN. Latent prostatic carcinoma: pathological and epidemiological aspects. Jpn J Clin Oncol 1989;19:319-26.
22. Shibata A, Whittemore AS, Imai K, et al. Serum levels of prostate-specific antigen among Japanese-American and native Japanese men. J Natl Cancer Inst 1997;89:1716-20.
23. Griffiths K. Estrogens and prostatic disease. International Prostate Health Council Study Group. Prostate 2000;45:87-100.
24. Messina MJ. Emerging evidence on the role of soy in reducing prostate cancer risk. Nutr Rev 2003;61:117-31.
25. Hillman GG FJ, Kucuk O, Yudelev M, Maughan RL, Rubio J, Layer A, Tekyi-Mensah S, Abrams J, Sarkar FH. Genistein potentiates the radiation effect on prostate carcinoma cells. Clin Cancer Res 2001;7:382-390.
26. Lee MM, Gomez SL, Chang JS, Wey M, Wang RT, Hsing AW. Soy and isoflavone consumption in relation to prostate cancer risk in China. Cancer Epidemiol Biomarkers Prev 2003;12:665-8.
27. Hussain M SF, Djuric Z, et al. Soy isoflavones in the treatment of prostate cancer. J Nutr 2002;132:575S-576S.
28. Zhao Y MB, Weaver CM. Calcium Bioavailability of Calcium Carbonate Fortified Soymilk Is Equivalent to Cow's Milk in Young Women. J Nutr 2005;135:2379-82.