Soy and Human Health

• The Astonishing Functional Food: Soy Protein and Soy Constituents
• Soy Protein and Coronary Heart Disease
• Soy and Digestive Tract Health
• Soy Foods in Chronic Renal Disease
• How Can Soy Help Diabetes?
• Soy Protein Enhances Energy, Stamina and Sport Performance
• Soy and Cancers
• Soy and Breast Cancer
• Soy and Menopausal Symptoms
• Soy and Pre-Menstrual Syndromes
• Soy and Bone Health
• Losing Weight Healthily with Soy
• Soy and Urological Cancer
• Soy Lecithin and Human Health
• Clinical Abstracts on Soy
• Soy Clinical Reviews in Reputable Medical Journals: 1995-2002

Soy and Cancers - Some recent clinical reviews

Thyroid Cancer

Thyroid cancer incidence is three times higher in women than men. It is one of the five most common types of cancer occurring in young women and in recent Asian immigrants. Female hormones and changeable lifestyle factors (e.g., dietary intake) may be important in thyroid carcinogenesis. A population-based case-control study of thyroid cancer in women, ages 20-74, was conducted in the San Francisco bay area. Of 817 cases, diagnosed in 1995-1998 (1992-1998 for Asian women), and identified through the cancer registry, 608 (74%) were interviewed. All three classes of phytoestrogens examined (isoflavones, coumestans, lignans) and four of the seven specific compounds were associated with a reduced risk of thyroid cancer. The odds ratio for the highest quintile of total phytoestrogen consumption compared with the lowest was 0.64 (95% confidence interval: 0.41-0.98). Risk reduction was apparent for both white and Asian women. Despite the association between soybean consumption and goiter, a major risk factor for thyroid cancer, soy-based foods and phytoestrogens in particular appear to be associated with a reduced risk of thyroid cancer in women. Possible mechanisms include antioxidant effects, direct effects on endogenous estrogen and thyroid hormone levels, or antiestrogenic effects resulting from competitive binding to the estrogen receptor.

Prostate Cancer

It has been observed that genistein induces apoptosis and inhibits growth and prostate-specific antigen (PSA) production and secretion in androgen-dependent (LNCaP) and androgen-independent (PC3 and VeCaP) prostate cancer cell lines. To determine the effect of soy isoflavones on serum PSA levels, patients received 100 mg soy isoflavones orally twice daily for a minimum of 3 mo in the absence of progression or toxicity. Serum levels of total genistein and daidzein, PSA, testosterone, insulin-like growth factor-1, and insulin-like growth factor binding protein-3 levels were measured and toxicity was assessed monthly. Forty-one patients were enrolled; 4 patients in group I, 18 in group II, and 19 in group III, with a median PSA level of 13.3 mg/L (391 pmol/L). Forty patients were evaluated for PSA response. A total of 226 mo of supplementation was given with a median of 6 mo per patient (range 1-10 mo). Three of 4 patients in group I, 15 of 18 in group II, and 6 of 19 in group III achieved stable disease. The rate of linear rise in serum PSA levels decreased by 71% (from 14% to 4%, P = 0.03) in group II and by 56% (from 27% to 16%, P = 0.07) in group III patients. Although significant increases in serum isoflavones were observed after supplementation, no significant changes were observed in serum levels of testosterone, insulin-like growth factor-1, or 5-hydroxy-methyl-deoxyuridine. Interestingly, insulin-like growth factor binding protein-3 level decreased significantly after soy isoflavone supplementation (P = 0.0007). Although the mechanism is unclear, soy isoflavones appear to decrease the rate of rise in serum PSA and stabilize the disease in patients with hormone-sensitive as well as hormone-refractory prostate cancer.

Breast Cancer

Debate exists over the possible effects of soy protein on breast tissue. A technique called Breast Enhanced Scintigraphy Testing (BEST) combines myocardial and breast imaging technologies into a single test that yields diagnostic information about myocardial function and distinguishes between normal breast tissue, inflammatory breast tissue, and carcinoma of the breast. To determine whether soy protein has any effect on inflammatory changes of the breast, women with inflammatory breast changes as defined by BEST imaging were asked to consume soy protein daily and were restudied 6 mo later. BEST imaging was performed on 197 women and 3 men over 2.5 y. There were 104 cases of women with inflammatory changes of the breast with a maximal count activity of 229 ± 50. Of these 87 women, 40 were started on a 24-g/d regimen of soy protein containing 160 mg isoflavones and 1000 mg saponins. Of the 40 women, 30 have been studied both before and after 6 mo of soy protein consumption. Of the 30 women studied to date, the maximal count activity was 245 ± 40 when initially evaluated by BEST imaging. After 6 mo of dietary supplementation with soy protein, the maximal count activity was 202 ± 32. Using a two tailed t-test for comparison, it was found that a statistically significant (P <0.05) difference between the inflammatory changes noted before and after soy protein consumption. No other dietary or lifestyle changes were reported by the women during follow-up evaluation. BEST demonstrated a reduction in breast inflammation in 30 women consuming daily soy protein during a 6-mo follow-up evaluation.

In a recent study suggests that increased, consistent isoflavone intake 40mg/day affects estrogen metabolism by altering the steroid hormone concentrations and menstrual cycle length, thereby demonstrating a potential for reducing the risk for breast cancer.