The Science of Soy - The East Viewpoints: Part A3 - Soy and Prostate Cancer in Japanese Men

Soy foods, including tofu have been in traditional Chinese diet over thousands of year, according to Chinese literature. The reduced risk of chronic disease, including metabolic syndrome such as cardiovascular diseases, obesity and diabetes and lesser menopause symptoms in advanced age, may be aided by eating a lot of soy food accompanied with large portion of vegetables and fruits. Indeed, according to the study, only 10% of women in the East are experience symptoms of menopause in advanced age compared to over 70% of their Western counterparts.
According to Dr. Mark Messina, Ph.D., Soy foods contributed from 6.5%8  to 12.8%7  of total protein intake in older adult in Japan.(b)

The approval of cardiovascular benefit of soy by FDA in 1999 accompanied with the discovery of health benefits in clinical studies over past decade, prompted the promotion and advertisement of soy's health benefits in every aspect in Western society. Evidences could be seen by walking through the supermarkets and drug  stores.  Soy supplements and products such as tofu, soy milk, soy-based infant formula, and meatless “texturized vegetable protein” burgers were widely available. According to the United Soybean Board’s 2004–2005, 25% of Americans consume soy foods or beverages at least once per week, and 74% view soy products as healthy.

Today, the promotion of soy are no longer existed, it may be results of discovery of adverse effect in single ingredient and animal studies, as intake of soy is associated to induce risk certain mammary cancers and infertility. The publication of the result have drawn many criticisms. According to Thomas Badger, director and senior investigator at the Arkansas Children’s Nutrition Center in Little Rock, these effects are seen only under certain experimental conditions that are not likely to occur in humans—and therein lies the crux of the debate(a). Equol (4',7-isoflavandiol), an isoflavandiol metabolized from daidzein may be the causes, as 90% of Eastern population are equol producers but only 30% in the West.
The explanation of the positive effect of soy isoflavones in reduced risk of mammary cancers by  University of Goettingen may be interesting, as researchers said" Most importantly, there is dispute as to whether isoflavones derived from soy or red clover have negative, positive or any effect at all on the mammary gland or endometrium. It is beyond any doubt that soy products may have cancer preventing properties in a variety of organs including the mammary gland. However, these properties may only be exerted if the developing organ was under the influence of isoflavones during childhood and puberty.

Soybean is the genus Glycine, belonging to the family Fabaceae, one of the legumes that contains twice as much protein per acre as any other major vegetable or grain crop, native to Southeast Asia. Now, it is grown worldwide with suitable climate for commercial profits.
Nutrients
1. Carbohydrates
2. Dietary fiber
3. Fat
4. Protein
5. Essential amino acid
6. Vitamin A
7. Vitamin B6
8. Vitamin B12
9. Vitamin C
10. Vitamin K
11. Calcium
12. Iron
13. Magnesium
14. Phosphorus
15. Potassium
16. Sodium
17. Zinc
18. Etc.
Phytochemicals
1. Isoflavones
2. Genistein
3. Saponins
4. Beta-sitosterol
5. Daidzein

I. Soy in Eastern population
A. The Japanese population
Japan, an island nation in the Pacific Ocean, lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south(1). According to Moriyama, Japanese women and men live longer and healthier than everyone else on Earth, it may be result of  healthier Japanese diet and lifestyle. According to the World Health Organization, the Japanese have an average of 75 years healthy living with disability-free, it may be due to average soy intake 10 to 70 times higher than in Western people(1a)(1b).

A3. Soy and Prostate cancer in Japanese Men
Prostate cancer is defined as a condition in which the cells of prostate has become cancerous, causing abnormal cell growth with possibility of spreading to the distant parts of the body. Most prostate cancers are slow growing and enlarged prostate and prostate cancer may be detected during physical (rectum) exams.

The widespread of prostate cancer, once considered a disease of aging male, now have become major concerns of governments and scientific community in South East Asian with tendency to effect even younger age population. Suggestions emerged of over consuming bad fats in any time in history accompanied with unhealthy diet and life style may be the possible causes of the disease, linking to the economic prosperity over 2 decades.

In fact, the incidence of prostate cancer in Asia is still lower if compared to their Western counterparts.
The Research Center for Cancer Prevention and Screening, National Cancer Center. suggested that isoflavones and soy food are associated with a dose-dependent decrease in the reduced risk of localized cancer, in a population-based prospective study in 43,509 Japanese men ages 45 to 74 years with  participants responded to a validated questionnaire, which included 147 food items. During follow-up from 1995 through 2004, 307 men were newly diagnosed with prostate cancer, of which 74 cases were advanced, 220 cases were organ localized, and 13 cases were of an undetermined stage(5).

Environment, Diet,  intestinal microbiota and Geography
The testing of North American Japanese and Japanese in Japan showed the environment factor may be involved in the development of prostate cancer regardless to genetic similarity(7). The incidence of the disease increased vary both from country to country and ethnic group, with the highest incidence reported for Afro-Americans and the lowest for Asian men(2).

 The study of  the associations between nutritional and other lifestyle factors and the prevalence of prostate cancer in a case-control study of Japanese men, showed that soy isoflavone significantly decreased the risk of prostate cancer regardless to the intake of other nutrients such as  PUFA, (n-6) fatty acids or magnesium from other food sources(9).

Other suggested that legumes (not limited to soy products) and certain categories of vegetables may protect against prostate cancer(10).

DR. Akaza H. said "not having equol converting bacteria in the intestine (non-equol producers) can be a risk factor for prostate cancer and that one direction for future research will be to examine the possibility of improving the intestinal environment to enable equol production"(13).

Genes differentiation
1n gene differentiation, estrogen related genes may be the culprits for the development of prostate cancer. In an one hundred and eighty cases and 177 controls selected from three geographic areas of Japan study,  though analysis by the multifactor dimensionality reduction method, soy isoflavones, showed to exhibit its anti prostate cancer, depending to differ between the genotypes of estrogen related genes(3).
According to Dr. Kimura T., the incidence of prostate cancer  in Asia is much lower than that in African Americans and European Caucasians and soy food consumption, more popular in Asian populations, is associated with a 25% to 30% reduced risk of prostate cancer, it may be as a result of  genetic mutation of approximately 30 genetic polymorphisms in populations of countries in the West.(1).

Serum of isoflavones
In a case-control study within the Japan Public Health Center-based Prospective of a total of 14,203 men aged 40 to 69 years who had returned the baseline questionnaire and provided blood samples observed from 1990 to 2005, showed that plazma genistein level is associated inversely to the risk of prostate cancer(4).

Other in the study of four isoflavonoids in plasma of 14 Japanese and 14 Finnish men, also showed  that the mean plasma  of total individual isoflavonoid levels of Japnaese are 7 to 110 times higher Japanese than in the Finnish men. Genistein, a tyrosine kinase inhibitor, occurred in the highest concentration(11).

In the experiment of  Urinary excretion of lignans and isoflavonoid phytoestrogens in Japanese men and women consuming a traditional Japanese diet showed that the excretion of isoflavonoids correlated with soybean-product intake is associated to reduced  mortality in breast and prostate cancer of Japanese women and men(12).

In view of above, the Loma Linda University, insisted that  soy isoflavones should be tested against different populations of prostate cancer patients for its efficacy(6). Other suggested that the lower incidence of prostate cancer in Japanese men may be a result of traditional Japanese diet with a lot of soy foods and fishes(8) and promotes the production of Soy-derived food products and the metabolization of the isoflavones to enhance equol production to those of non producers of Asian and European/North American populations(13).

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References
(1) East meets West: ethnic differences in prostate cancer epidemiology between East Asians and Caucasians by Kimura T.(PubMed)
(2) Hereditary prostate cancer and other genetic predispositions to prostate cancer by Cussenot O¹, Valeri A, Berthon P, Fournier G, Mangin P.(PubMed)
(3) Polymorphisms in estrogen related genes may modify the protective effect of isoflavones against prostate cancer risk in Japanese men by Sonoda T¹, Suzuki H, Mori M, Tsukamoto T, Yokomizo A, Naito S, Fujimoto K, Hirao Y, Miyanaga N, Akaza H.(PubMed)
(4) Plasma isoflavones and subsequent risk of prostate cancer in a nested case-control study: the Japan Public Health Center by Kurahashi N¹, Iwasaki M, Inoue M, Sasazuki S, Tsugane S.(PubMed)
(5) Soy product and isoflavone consumption in relation to prostate cancer in Japanese men by Kurahashi N¹, Iwasaki M, Sasazuki S, Otani T, Inoue M, Tsugane S; Japan Public Health Center-Based Prospective Study Group.(PubMed)
(6) An overview of the health effects of isoflavones with an emphasis on prostate cancer risk and prostate-specific antigen levels by Messina M¹, Kucuk O, Lampe JW.(PubMed)
(7) Prostate cancer in native Japanese and Japanese-American men: effects of dietary differences on prostatic tissue by Marks LS¹, Kojima M, Demarzo A, Heber D, Bostwick DG, Qian J, Dorey FJ, Veltri RW, Mohler JL, Partin AW.(PubMed)
(8) A case-control study of diet and prostate cancer in Japan: possible protective effect of traditional Japanese diet by Sonoda T¹, Nagata Y, Mori M, Miyanaga N, Takashima N, Okumura K, Goto K, Naito S, Fujimoto K, Hirao Y, Takahashi A, Tsukamoto T, Fujioka T, Akaza H.(PubMed)
(9) Nagata Y¹, Sonoda T, Mori M, Miyanaga N, Okumura K, Goto K, Naito S, Fujimoto K, Hirao Y, Takahashi A, Tsukamoto T, Akaza H.(PubMed)
(10) Vegetables, fruits, legumes and prostate cancer: a multiethnic case-control study by Kolonel LN¹, Hankin JH, Whittemore AS, Wu AH, Gallagher RP, Wilkens LR, John EM, Howe GR, Dreon DM, West DW, Paffenbarger RS Jr.(PubMed)
(11) Plasma concentrations of phyto-oestrogens in Japanese men by Adlercreutz H¹, Markkanen H, Watanabe S.(PubMed) (12) Urinary excretion of lignans and isoflavonoid phytoestrogens in Japanese men and women consuming a traditional Japanese diet by Adlercreutz H¹, Honjo H, Higashi A, Fotsis T, Hämäläinen E, Hasegawa T, Okada H.(PubMed)
(13) Prostate cancer chemoprevention by soy isoflavones: role of intestinal bacteria as the "second human genome" by Akaza H.(PubMed)