Health Effects of Soy Beans


Miso, soy sauce, tempeh, tofu—these and other foods derived from soybeans have been a cornerstone of Asian cuisine and nutrition for centuries.  Not until World War II, however, were soybeans introduced to US as a substitute for other protein-rich foods and as a source of edible oil.

Therapeutic Uses

Soy is widely consumed in the Asian diet.  Its therapeutic uses are mainly for[3]:

  • Protein Source
    • Contains a full complement of essential amino acids, making it a complete protein[21,22]
  • Heart Health[2,3]
    • In 2006, an American Heart Association review concluded that soy bean may confer benefits to cardiovascular health for the following reasons:
      • Their high content of protein, omega-3 fatty acids, tryptophan, fiber, iron, and a bunch of other minerals..
      • If you use soy beans or products to replace foods high in animal protein, which contains saturated fat and cholesterol.
      • Soybeans are 5% saponins which act like soap, emulsifying fats and binding to cholesterol, thereby interfering with its absorption into the body. This action may help reduce blood cholesterol levels.

Some other studies have also found that soy beans and products may offer protection against:

  • Menopausal symptoms
  • Cancer[1,2,15,16,17]
  • Osteoporosis[18]

Good vs. Bad Soy Products

Large epidemiological studies in Asian countries have shown that lifelong traditional consumption of soy may offer some protection against menopausal symptoms, breast cancer, and osteoporosis.  However, studies in non-Asian populations have yielded conflicting results.


The differences may come from three reasons in author's own opinion:

  • Good vs. bad soy products
    • Bad
      • Highly processed soy bean products which are made with soy protein isolate, preservatives, and food additives.
        • In Dr. Kim's opinion[4], they’re no better than French fries, donuts, and regular fast food fare.
      • Unfermented soy products contain[8,25]
        • High levels of phytic acid or phytates which blocks the absorption of essential minerals like calcium,[33] magnesium, iron, and especially zinc in the intestinal tract. 
        • Trypsin inhibitors and hemaglutinin that stunt human growth
        • Researchers have discovered that consuming unfermented soy may be linked to reduced male fertility[26], increased cancer risk, damaged brain function, developmental abnormalities in infants, and early onset of puberty.
    • Good
      • Good soy beans and products include whole soy beans (or Edamame[12]) and fermented soy products.  Examples of fermented soy products include:
        • Miso[13]
        • Fermented bean curd[6](豆腐乳)
        • Natto[9]
        • Tempeh[10]
        • Doenjang  (Korean version of miso)[11]
        • Naturally fermented soy sauce[14] 
        • Stinky Tofu[24]
      • The fermentation process removes the phytates, trypsin inhibitors and hemaglutinin. 
      • Fermented soy foods have long been a staple in Asian diets and are generally beneficial when combined with other foods such as rice, sea foods, fish broth, organ meats and fermented vegetables.
      • Fermented soy products have more bioactive molecules than those that are non-fermented. This is because beta glucosidase from bacteria cleaves sugar off isoflavones in soy, converting them into the active compounds diadzein, genistein, and glycetein.
      • Note that Dr. Brownstein has a different opinion on edamame.  He says that we should also avoid it.
  • Different physiology
    • Traditionally soy products have been consumed by Asians, but not non-Asians, regularly for centuries.
    • In [7], it shows that the guts of different primates can be fine-tuned to their diet in very sophisticated ways.  
    • In [19], Dr. Agus has suggested that:
      • Studies carried out at the renowned Mayo Clinic in Rochester, Minnesota, may not have much significance to people who live in other regions of the country, say Newark, New Jersey, or New Orleans, Louisiana.  The reason for this has everything to do with demographics and the genetics of ethnicity.
  • GMO vs. non-GMO
    • Most soy beans grown in America is GMO, which is stringently regulated by EU, while non-GMO soy beans are grown in Asian countries (especially in Japan) if traditional farming is practiced.

Anti-Cancer Properties[1,2,16,17]

Of any plant, soy contains the highest concentration of isoflavones, a class of phytoestrogen compounds that are structurally similar to estrogen.  Isoflavones in soy products are anti-proliferative, anti-oxidant, and anti-inflammatory and demonstrate activity against cancer in multiple studies. The antiangiogenic activity of genistein was initially detected in a study of healthy Japanese individuals who consumed a traditional soy-rich Japanese diet. Their urine was found to contained genistein and daidzein and to inhibit angiogenesis in cultured cells. In men who consumed a Japanese versus Western diet, urinary genistein was 7052 nmol/day compared to 184.4 nmol/day, respectively.


In prostate cancer patients, drinking 500 mL of soy a day for 6 months either reduced their levels of prostate-specific antigen (PSA) or prolonged PSA doubling time by more than two times. Soy’s effects on colorectal cancers have also been studied.


A study of over 73,000 women in China showed that daily intake of soy products such as soy milk, tofu, and fresh soybeans decreased premenopausal breast cancer risk. Likewise, American women of Asian descent who consume a traditional soy-based diet have a low incidence of breast cancer. Early soy intake (>1.5 times per week) during childhood was found to reduce later breast cancer risk by 58% in a study of Asian women in California and Hawaii. Similarly, Japanese men in Hawaii who consume a high soy diet had low mortality from prostate cancer.


Soy products may also be effective against recurring breast cancer among survivors. A Chinese study found 5,000 breast cancer survivors on a soy-rich diet (greater than 15.5 grams a day) were at lower risk for cancer recurrence and mortality.

Recommendations

Try to consume fermented soy products more and unfermented ones less.  Because most fermented soy products are salty, you should consume them in moderation[4,8,20].  Another reason for you to consume soy foods in moderation is that: 

  • The soybean isoflavones, genistein and daidzein, have been found to inhibit thyroid hormone synthesis[32,34-38]
  • “Some studies show that if you eat a lot of soy, or drink a big glass of soy milk, within one hour of taking a thyroid hormone, it might affect absorption,” Dr. Nasr says.[34]

You should also choose organic soy products over Genetically Modified soy products.


Finally, based on a review paper and other researches[23,27,28], you should NOT feed infants with soy-based formula.  On the other hands, early and exclusive breastfeeding provides immunological protection against infectious diseases and well as reduced risk of chronic diseases for both mother and child[31].  


References

  1. The Soy - Breast Cancer Controversy (The University of Texas MD Anderson Cancer Center)
  2. Edamame (Eat to Defeat Cancer)
  3. National Geograpic Guide to Medicinal Herbs
  4. Soy Health by Dr. Ben Kim
  5. Fermented bean curd (Wikipedia)
  6. 营养食品—豆腐乳
  7. Human Ancestors Were Nearly All Vegetarians 
  8. Dangers of soy
  9. Nattō
  10. Tempeh
  11. Doenjang
    • In traditional Korean cuisine, jukyeom (죽염, 竹鹽), which means "bamboo salt", is prepared by roasting salt at temperatures between 800 and 2000 °C[12] in a bamboo container plugged with mud at both ends. This product absorbs minerals from the bamboo and the mud, and has been shown to increase the anticlastogenic and antimutagenic properties of the fermented soybean paste known in Korea as doenjang.
  12. Edamame (Wikipedia)
  13. Miso (Wikipedia)
  14. Soy Sauce (Wikipedia)
  15. Consuming Soy Early in Life May Reduce Later Breast Cancer Risk
  16. Shu XO, et al. Soy and intake and breast cancer survival.  JAMA 302(22):2437-2443, 2009. 
  17. Guha N, et al. Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study.  Breast Cancer Res Treat 118:395-405, 2009.
  18. Soy foods: are they useful for optimal bone health?
  19. The End of Illness by David B. Agus, MD
  20. THE PLOY OF SOY by: Fallon, Sally
  21. Soy Benefits National Soybean Research Laboratory
  22. Nutrition Facts of Tofu 
    • Protein quality = 106
  23. Soy, phyto-oestrogens and male reproductive function: a review.
  24. Stinky Tofu (Wikipedia)
  25. Did You Know That Raw Soybeans Are Toxic?
  26. Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic
  27. Infant feeding with soy formula milk: effects on puberty progression, reproductive function and testicular cell numbers in marmoset monkeys in adulthood
  28. Infant feeding with soy formula milk: effects on the testis and on blood testosterone levels in marmoset monkeys during the period of neonatal testicular activity
  29. Soy Isoflavones (Linus Pauling Institute)
  30. The Soy Controversy
  31. Ip S, Chung M, Raman G, ChewP, Magula N, DeVine D, Litt M, Trikalinos T, Lau J. Breastfeeding and maternal and infant health outcomes in developed countries. Evidence Report/Technology Assessment Number 153. 2007 April; AHRQ Publication No. 07-E007.
  32. Hendler SS, Rorvik DM, eds. PDR for Nutritional Supplements. 2nd ed. Montvale: Thomson Reuters; 2008.
  33. The Effect of Phytic Acid on the Absorption of Calcium and Phosphorus
    • The effect of phytate was: (1) a great reduction in the absorption and retention of calcium; (2) an increase in the absorption and retention of phosphorus.
  34. Thyroid Issues? What You Need to Know About Diet and Supplements
  35. Brent GA. Environmental Exposures and Autoimmune Thyroid Disease. Thyroid 2010 July; 20(7): 755—761. doi: 10.1089/thy.2010.1636
    • Soy protein and soybean isoflavones have been associated with reduced T4 absorption (important for hypothyroid infants on soy formula), interference with thyroid hormone action, and, in a few studies, increased thyroid autoimmune disease
    • In clinical studies, the usual intake of dietary soy in those with normal thyroid function has no consistent adverse effects
    • Most studies of isoflavone interference with thyroid hormone action have been in vitro
    • A case–control study of children with autoimmune thyroid disease showed that cases received significantly more soy formula as infants compared to their nonaffected sibling controls 
  36. de Souza dos Santos MC, Goncalves CFL, Vaisman M et al. Impact of flavonoids on thyroid function. Food and Chemical Toxicology, Volume 49, Issue 10, October 2011, Pages 2495-2502.
  37. Doerge DR and Chang HC. Inactivation of thyroid peroxidase by soy isoflavones, in vitro and in vivo. Journal of Chromatography B, Volume 777, Issues 1—2, 25 September 2002, Pages 269-279.
  38. Messina M and Redmond G. Effects of Soy Protein and Soybean Isoflavones on Thyroid Function in Healthy Adults and Hypothyroid Patients: A Review of the Relevant Literature. Thyroid. March 2006, 16(3): 249-258.
    •  Some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients
    •  It is important for soy food consumers to make sure their intake of iodine is adequate

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