Soy protein is far from the miracle food that some have claimed.  However, soy, especially tofu, has been found to have a small but significant effect in decreasing mortality rates.  Tofu is salt free and non-fermented.  In Champaign-Urbana, it can be purchased most cheaply at the Am-Ko food store. Soy sauce, in contrast, is extremely high in salt and is fermented.  Soy sauce is the primary cause of the very high stroke death rates in parts of Japan.  Fermentation creates carcinogens and is the primary cause for the high rates of stomach cancer in the Far East.

Bone Might be Preserved by Soy: Soy reportedly reduces heart disease and breast cancer. Two animal studies have found that soy decreases bone loss. Estrogen isoflavones daidzein and genistein may be reason. Sci News 1/2/99. Also Am J Clin Nutr ’98 68(suppl):1358S-63S

Bone: Soy Isoflavone Helps Bone in Women: First prospective controlled study of 69 women found less lumbar spine bone loss over 24 weeks in DB study. Am J Clin Nutr 2000 Sep;72(3):844-52

Bladder Cancer Increased by Soy: In the Singapore Chinese Health Study, 329,848 person-years of follow-up were accrued. Sixty-one bladder cancer cases were identified. The highest quartile of total soy intake (> or =92.5 g/1000 Kcal) was associated with a 2.3-fold increase in bladder cancer risk compared to the lowest after adjustment for cigarette smoking and level of education. Similar results were obtained for intakes of soy protein and soy isoflavones. Dietary soy and increased risk of bladder cancer: the Singapore Chinese Health Study. Sun CL, Yuan JM, Arakawa K, Low SH, Lee HP, Yu MC. University of Southern California. Cancer Epidemiol Biomarkers Prev. 2002 Dec;11(12):1674-7

Breast Cancer: Genistein Prevent Mice Breast Cancer: Am J Clin Nutr 12/98 suppl. High intake assoc with less human breast CA, e.g. Japan and Singapore. US 6-fold more breast cancer. High intake soy product = 4g soy protein/day. Soy milk=3% soy protein. Protective effect of soy substantially weaker among US-born Asian than non-US-born Asian-Am. ***. So soy may only be a marker for some other protective element.

Colon Cancer Decreased by Soy in Mice: Am J Clin Nutr 68(suppl):1394S-9S, ’98. Populations consuming soy have lower colon cancer. (Nutr Cancer ’94, 21:113-31) Genistein decreased rat precancerous lesions. The amount of phytochemicals in soy protein isolate is much lower than in soybeans and the isolate didn’t work as well.

Endometrial Cancer: Soy Associated with Less: Hawaiian study found highest soy (especially tofu) was associated with a risk rate of just RR 0.50 for endometrial cancer. Am J Clin Nutr 12/98.

Heart Attacks: Soy four time per week best: In a case control study of 600 acute heart attack victims and 1200 controls, vegetables showed no clear association with the risk of acute heart attacks, but fruit consumption appeared to reduce the risk in both men and women. The results also suggested that fish consumption was related to a decreased risk in men, although the trend was not statistically significant. In women only, tofu consumption was inversely related to the risk of heart attacks; relative risks for eating tofu <2, 2-3, and 4 times per week were 1.0, 0.8, and 0.5. Jpn Circ J 2001 Mar;65(3):200-6

Mortality: Soy Lowers Overall Mortality a Little in Japan: 29079 Japan followed over 7 years of follow-up, 2,062 participants (1,163 men and 899 women) died. The highest compared with the lowest quintile of total soy product intake was marginally significantly inversely associated with total mortality after adjustment for total energy and nondietary covariates (hazard ratio = 0.83). For women but not for men, n-3 fatty acids from fish were significantly inversely associated with total mortality. Results showed that soy intake may have moderate but beneficial effects on total mortality. Soy and fish oil intake and mortality in a Japanese community. Nagata C, Takatsuka N, Shimizu H. Gifu University, Japan. Am J Epidemiol. 2002 Nov 1;156(9):824-31.

Mortality: Small Differential Fish/Soy Benefit in Japan: 29000 adults 7 yr f/u with 2000 dying. High soy intake modest beneficial effect on mortality and fish only significant for females. However, even low intake quartile consumed 410 mg omega-3 per day v 800-1000 average and 1600 mg high with 0.87 HR males and 0.77 females p=0.38 for males. High soy 166 g/d v 40 g/d for low with HR 0.83 both sexes. Am J Epid ’02;156:824-31. 

Osteoporosis: Soy Protein No Help for Post-Menopausal Bones, Lipids, or Mental Functioning: In a DB PC study of 202 postmenopausal women given 25.6 g of soy protein containing 99 mg of isoflavones (52 mg genistein, 41 mg daidzein, and 6 mg glycetein or total milk protein as a powder on a daily basis for 12 months, cognitive function, bone mineral density, or plasma lipids did not differ significantly between the groups after a year. Effect of soy protein containing isoflavones on cognitive function, bone mineral density, and plasma lipids in postmenopausal women: a randomized controlled trial. Kreijkamp-Kaspers S, Kok L, Grobbee DE, de Haan EH, Aleman A, Lampe JW, van der Schouw YT. University Medical Center Utrecht, The Netherlands. JAMA. 2004 Jul 7;292(1):65-74

Prostate Cancer: Soy Milk Decreases: In a prospective study with 225 incident cases of prostate cancer in 12,395 California Seventh-Day Adventist men who in 1976 stated how often they drank soy milk., frequent consumption (more than once a day) of soy milk was associated with 70 per cent reduction of the risk of prostate cancer (relative risk = 0.3). Cancer Causes Control 1998 Dec;9(6):553-7

Stomach Cancer: Tofu Decreases, Salty Soy, Kimchi Increase: Case control and cohort studies show ginseng decreased the risk. Also, a recent case control study shows broiling or stewing meat increases the risk but pan frying does not. Salted fish, and salty soybean paste stews increase the cancer, while tofu, unfermented cabbage, spinach, sesame oil decrease the risk. Stomach cancer is the most prevalent cancer in Korea. Pickled vegetables, the very popular kimchi, increase the risk. Int J Cancer ’97;Suppl 10:7

Cholesterol: Increased HDL, Decreased LDL: With a diet of 40 grams of soy protein/day, especially if high in isoflavone soy protein which had 60% more. Sue Potter, U Ill, Urb-Ch Division of Nutr Sci. US men 6-fold more CHD death between 40-69 yo than Japan. And 8-fold difference for women. Benefit of soy not much from oil and protein hydrolysates do reduce

Protects DM Kidney: James Anderson, U Ky, Am J Clin Nutr ’98 68(suppl):1347S-53S

Soy Helps: Soy protein reduces heart disease and breast cancer. Two animal studies now suggest may help prevent osteo. Ovarectomized rates fed soy reverse bone loss (12/98 Am J Clin Nutr) maybe due to estrogenlike isoflavones daidzein and genistein.

Bone: Soy Isoflavones Help Lower LDL & Increase Bone Density: DB PC 6 months 40g/d soy protein with two levels of isoflavones/g vs milk protein. Both soy lowered LDL but only higher soy increases lumbar bone density. U Ill, Am J Clin Nutr 12/98;68(6 Suppl):1375; Same in another U Ill study of LDL. Am J Clin Nutr 9/98;68:545

Thomas E. Radecki, M.D., J.D.

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