Nutrients
Soybeans are an excellent source of protein and molybdenum. They are a very good source of iron, calcium, phosphorus, and dietary fiber. They are a good source of vitamins B1, B2, B6, and E and folic acid. They also contain other health promoting compounds, including phytosterols, lecithin, isoflavones, phytoestrogens, and protease inhibitors. The amino acid profile of soy is a little low in methionine and tryptophan, but is still regarded as an excellent source of protein, soybeans (38% protein), soy flour (40 to 50% protein), soy protein concentrates (70% protein), and soy protein isolates (90 to 95% protein).

Reduce LDL Cholesterol
Increased consumption of soy foods has been associated with reduction in LDL cholesterol in both clinical and observational studies. Human studies have also shown that soy protein is effective in lowering plasma cholesterol, LDL cholesterol and triglyceride concentrations.

In one 8-week randomized, placebo-controlled trial in 117 patients with high cholesterol levles, LDL cholesterol was significantly reduced by 5.9% after consuming 15-25g/day of soy protein.

A meta-analysis of thirty studies concluded that a daily dietary intake of 25g of soya protein resulted in small, highly significant reductions in total and LDL cholesterol (-6%)

A preparation combining isolated soy protein with soy fibers and phospholipids has been shown to have twice the lipid-lowering effect of a preparation containing isolated soy protein alone.

Cancer Prevention
Soybean consumption is thought to be one of the major reasons for the relatively low rates of breast cancer and prostate cancer in Asian countries.

The isoflavones daidzein and genistein, found in soybeans and soy products have been shown in epidemiological studies to be protective against breast cancer and prostate cancer.

These two isoflavones act as phytoestrogens (dietary estrogens) that reduce the effects of estrogen, neutralizing some of estrogen’s cancer causing potential.

Although there no studies demonstrating an increase in the risk of breast cancer among women eating soy, there is suggestion that soy phytoestrogens can behave like estrogen and potentially increase breast cancer risk. Test tube studies have shown that genistein stimulates the growth of estrogen-positive breast cancer tumors, and women with this type of breast cancer tumor should avoid soy.

Results of numerous studies are suggestive of a possible relationship between phytoestrogen intake and reduced prostate cancer risk.
The results of the Japan Collaborative Cohort Study suggest that a high intake of soy bean curd (tofu) might have preventive effects against the risk of ovarian cancer.

Testosterone
There has been some evidence suggesting a mild inverse relationship between soy protein intake and testosterone levels in males. A study published in the Journal of the International Society of Sports Nutrition concluded that a 12-week supplementation with soy protein did not decrease serum testosterone or inhibit lean body mass changes in subjects engaged in a resistance exercise program.

Another study suggests that higher intake of soy foods and soy isoflavones is associated with lower sperm concentration. Population statistics are however contradictory to this result.

Coronary Artery Disease
In a study of forty-one hyperlipidemic men and postmenopausal women it was concluded that consumption of soy products reduces coronary artery disease risk because of both modest reductions in blood lipids and reductions in LDL cholesterol, homocysteine, and blood pressure.