Soy is an excellent source of protein. One-half cup of cooked soybeans has 14 grams of proteins and 4 ounces of tofu has 13 grams of protein. This is about twice the protein found in one large egg or one 8-ounce glass of skim milk, and two-thirds the amount of protein in 3 ounces of lean ground beef.

Unlike animal sources of protein (e.g., beef, chicken), soy contains no cholesterol and very little saturated fat. In addition, soybeans are the only plant source of protein that provides a “complete” protein – a protein that contains all the amino acids essential to human growth and development.

Soy is also high in fiber and rich in B vitamins and polyunsaturated fats. It is rich in essential fatty acids such as omega-3 fats, which are vital to human health.

People who replace even a small amount of their meat protein intake with soy products can achieve a reduction in their intake of calories, saturated fat and cholesterol. There is some evidence that soy foods may help with blood sugar control and may also help lower the risk for some of the possible complications of diabetes.

There is conflicting evidence about the role of a soy diet in helping prevent or reduce symptoms associated with various illnesses and conditions. They include:

• Cancer. The evidence on the relationship between soy and cancer remains cloudy. Some studies suggest that soy components may prevent the growth and spread (metastasis) of cancer tissue and tumors in some areas of the body. There are a variety of compounds found in soy foods with possible anti-cancer activities. However, other studies appear to show that soy consumption may actually raise the risk of some types of cancer by interacting with the hormone estrogen in a negative way. Some physicians now recommend that patients avoid soy if they have certain forms of cancer (e.g., cancer of the breast, ovaries or uterus) as well as those with a family history of estrogen-dependent breast tumors. 
  
  One recent, large study even found that while a soy-rich diet decreases the risk of localized prostate cancer, it may actually increase the risk of advanced prostate cancer. The researchers theorize that this contradictory conclusion may be the result of how tumors change over time. Or, it may result from how soy interacts with different kinds of tumor subtypes.

  Some physicians now recommend that patients avoid soy if they have certain forms of cancer (e.g., cancer of the breast, ovaries or uterus) or if they have a family history of estrogen-dependent breast tumors.

   
• Cholesterol. In recent years, the American Heart Association (AHA) and the U.S. Food and Drug Administration (FDA) have both recommended that people with high cholesterol eat more soy protein on a daily basis. The recommendation followed a number of studies that appeared to find that soy protein intake was found to help reduce blood lipid levels (e.g., LDL cholesterol and triglycerides). Some recent studies appear to back up this claim. Tulane University in Louisiana conducted a study that linked increased soy intake with lower total cholesterol. However, recent studies have cast doubt on the cholesterol-reducing benefit of a diet high in soy proteins. For more information, see Ongoing research.
  
  
• Diarrhea in children. Infants and young children (up to 3 years old) who have diarrhea often experience fewer bowel movements and a reduction in the incidence of diarrhea after switching to soy formula.
  
  
• Menopause. Many women consume soy products or take isoflavone supplements to relieve symptoms of menopause. Research in this area is still in the preliminary stages. However, because soy contains a plant estrogen (phytoestrogen) that is similar in structure to the estrogen produced in the human body, some researchers speculate that increasing the intake of these phytoestrogens could help reduce the severity of menopausal hot flashes.
  
  
• Osteoporosis. Many soy products contain calcium and isoflavones, both of which have been associated with reducing the risk of osteoporosis. However, not all soy products are good sources of calcium. The AHA recently stated that evidence of soy’s power in preventing or reducing risks of osteoporosis appears to be mixed. 
  
  In fact, a recent study found a strong link between consuming soy protein supplements and reduced bone loss in nonobese, postmenopausal women. However, not all soy products are good sources of calcium. In addition, the AHA recently stated that evidence of soy’s power in preventing or reducing risks of osteoporosis appears to be mixed.

Researchers continue to study the health effects of soy foods. The following are some of the possible health benefits of soy, although further research is necessary before a recommendation can be made:

• Reduce high blood pressure
  
  
• Prevent the growth of cancer tissue and tumors in some areas of the body
  
  
• Maintain bone density
  
  
• Strengthen the immune system
  
  
• Control blood sugar levels in diabetics
  
  
• Reduce inflammation

Certain bacteria found in the intestines that promote better health (probiotics) can be found in some unpasteurized and fermented soy products. Probiotic foods contain these friendly bacteria and help protect these bacteria from stomach acids and other unfriendly bacteria.

Probiotics may produce several desirable effects in the body, including helping to control cholesterol levels, manufacturing vitamins, acting as an anti-carcinogenic (cancer) agent, relieving symptoms of anxiety, enhancing bowel function, and recirculating hormones (like estrogen) back into the bloodstream.

There are many different components in soybeans that are being studied for possible health effects. These components and the proposed health benefits include: