Soy contains several well-researched compounds. Among the most well known are the isoflavones. There are three main isoflavones: genistein, daizein, and glycitein. Each of these has two different forms; the glycosylated form that is high in soybeans, and the aglycone form, which is high in fermented soy products such as tempeh.
Soy isoflavones are phytoestrogens. This means that they bind estrogen receptors and have estrogen-like biological activity. However, they are not a steroid molecule, like estrogen. Their activity can have a pro- or an anti-estrogen effect, depending on the cellular circumstance and given disease processes.
Because of this dual effect, soy isoflavones are known as an adaptogen. If there is not enough estrogen activity in the body, soy isoflavones will have a pro-estrogen effect by increasing the binding at estrogen receptors. If there is too much estrogen binding occurring, then the soy isoflavones will competitively bind the receptors and decrease the cellular response to estrogen.
The above described mechanisms allow soy isoflavones to be helpful in situations where more estrogen is needed, as well as those where less estrogen activity is required.
As the name implies (soy isoflavone), soy protein is extremely high in isoflavones. There are 2 milligrams of genistein and 2 milligrams of daizein per gram of soy protein. Genistein comprises roughly 50% of the total isoflavones in soy protein, whereas daizein is 40% and glycitein is only 10%. 
Soy isoflavones are considered to be anti-oxidants, anti-carcinogenic, anti-atherosclerotic, hypolipidemic, and anti-osteoporosis. They are an effective treatment option for heart disease, cancer, menopause, and osteoporosis.
- Soy isoflavones are an effective addition to any treatment protocol for heart disease and can also be used to prevent heart disease.
- Soy isoflavones are effective for individuals with high blood lipids as well. They can lower triglycerides and total cholesterol.  Soy isoflavones have also been shown to lower lower LDL, or bad cholesterol, levels. 
- Soy isoflavones can also help prevent heart disease by lowering homocysteine, an independent marker for heart disease risk. Supplementing with soy isoflavones can also reduce blood pressure. 
- Atherosclerosis can be prevented with soy isoflavones, due to the anti-oxidant activity, reducing oxidized LDL; which is implicated as one of the initial steps in the development of atherosclerosis. 
- Soy isoflavones are an effective treatment for menopausal complaints. They have been shown to increase cognitive function in postmenopausal women. Specific areas that have been affected in study include verbal memory and overall ability to learn new tasks. 
- Hot flashes can also be treated using soy isoflavones; particularly reductions in the severity and occurrences of hot flashes. 
- Women who suffer from menstrual migraines can use soy isoflavones as a prophylactic treatment to prevent recurrence. Studies have shown that soy isoflavones can reduce occurrence by as much as 50%. 
- Soy isoflavones can help prevent and treat osteoporosis. They have been shown to decrease bone resorption in postmenopausal women, who are most at risk due to the lack of estrogen. 
- Soy isoflavones are equally beneficial for individuals with diabetes. They have been shown to improve blood lipids in those with Type II diabetes, as well as to improve kidney function in diabetics with nephropathy.  In another study, they were proven to decrease insulin resistance at the tissue, improve glycemic control, and decrease overall cardiovascular risk associated with diabetes. 
- Finally, soy isoflavones can be protective against the development of hormone sensitive cancers such as breast and prostate cancers. Soy isoflavones were shown to be preventative against the development of breast cancer in premenopausal women.  They are also an effective and safe treatment for hot flashes for postmenopausal women who have a history of breast cancer and cannot take estrogen. Supplementation of soy isoflavones has shown to reduce cellular markers in the blood that are related to prostate cancer risk such as the PSA test.  This may prove to be a protective effect.
The recommended daily intake of soy isoflavones to achieve therapeutic effect is 50 mg of soy isoflavones per day. Many supplements will state the isoflavone content contained in the product. Soy protein contains approximately 5 mg of isoflavones per gram. Therefore, if one consumes 10 grams of soy protein, the recommended 50 mg of isoflavones will be met.
There are no side effects associated with the use of soy isoflavones. Soy isoflavones should be used with caution in men with prostate cancer or women with breast cancer, or those with a family history of these diseases. Women who are pregnant or nursing should not take soy isoflavones in amounts exceeded normal dietary intake due to the lack of long-term studies in these populations. 
1. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Soy isoflavones. March 2005.
2. Wang Y, Jones PJ, Ausman LM, Lichenstein AH. Soy protein reduces triglyceride levels and triglyceride fatty acid fractional synthesis in hypercholesterolemic subjects. Atherosclerosis. 2004 Apr; 173(2): 269-275.
3. Jenkins DJ et al. Effects of high and low isoflavone soy foods on blood lipids, oxidized LDL, homocysteine, and blood pressure in hyperlipidemic men and women. Am J Clin Nutr. 2002 Aug; 76(2): 365-372.
4. Jenkins DJ et al. Effects of high and low isoflavone soy foods on blood lipids, oxidized LDL, homocysteine, and blood pressure in hyperlipidemic men and women. Am J Clin Nutr. 2002 Aug; 76(2): 365-372.
5. Jenkins DJ et al. Effects of high and low isoflavone soy foods on blood lipids, oxidized LDL, homocysteine, and blood pressure in hyperlipidemic men and women. Am J Clin Nutr. 2002 Aug; 76(2): 365-372.
6. Kritz-Silverstein D et al. Isoflavones and cognitive function in older women: The Soy and Postmenopausal Health in Aging (SOPHIA) Study. Menopause. 2003 May-Jun; 10(3): 196-202.
7. Burke GL et al. Soy protein and soy isoflavone effects on vasomotor symptoms in peri- and postmenopausal women: The Soy Estrogen Alternative Study. Menopause. 2003 Mar-Apr; 10(2): 147-153.
8. Burke BE, Olson RD, Cusack BS. Randomized controlled trial of phytoestrogen in prophylactic treatment of menstrual migraine. Biomed Pharmacother. 2002 Aug; 56(6): 283-288.
9. Herkenss LS et al. Decrease bone resorption with soy isoflavone supplementation in postmenopausal women. J Women’s Health. (Larchmt) 2004 Nov; 13(9): 1000-1009.
10. Teixeira SR et al. Isolated soy protein consumption reduces urinary albumin excretion and improve serum lipid profile in men with type II diabetes mellitus and nephropathy. J Nutr. 2004 Aug; 134(8): 1874-1880.
11. Jayagopal V et al. Beneficial effects of soy phytoestrogen intake in postmenopausal women with type II diabetes. Diabetes Care. 2002 Oct; 25(10): 1709-1714.
12. Maskarinec G et al. Effects of a 2-year randomized soy interaction on sex hormone levels in premenopausal women. Cancer Epidemiol Biomarkers Prev. 2004 Nov; 13(11): 1736-1744.
13. Kumar NB et al. The specific role of isoflavones in reducing prostate cancer risk. Prostate. 2004 May 1; 59(2): 141-147.
14. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Soy isoflavones. March 2005.