There are health benefits to soy, but many of them have since been proven to not be as beneficial as previously thought according to a large body of emerging research. Soy is soy safe? Do the benefits of eating soy outweigh the risks?
The Popularity of Soy
The upswing in soy consumption in the US as a healthy food was in direct response to the October 26, 1999, statement released by the FDA that authorized the use of health claims about the role of soy protein in reducing the risk of coronary heart disease (CHD) on labeling of foods containing soy protein.
In 2000, the American Heart Association (AHA) Nutrition Committee released a scientific advisory on soy protein and coronary heart disease. At that time, the conclusion was that "it is prudent to recommend including soy protein foods in a diet low in saturated fat and cholesterol. Since then, many well-controlled studies on soy protein and soy-derived isoflavones substantially added to the knowledge base. However, recent studies since 2006 suggests that soy's cardiovascular benefits may have been overestimated by the early studies that formed the basis for its health claim.
Soy Nutritional Benefits
Soy beans are rich source of protein, including all essential amino acids (the only such vegetable source). Soy beans are also a rich source of calcium, iron, zinc, phosphorus, magnesium, B-vitamins, omega 3 fatty acids and fiber.
Soy and Health
There are healthy reasons to eat soy in moderation.
• There are limited studies that indicate that soy improves bone health, since by replacing animal protein with soy protein may help to prevent calcium loss from the bones.
• Recent study shows that soy has low glycemic index, so they do not raise blood sugar levels as other carbohydrates.
• Soy lowers blood cholesterol when it is combined with a diet low in saturated fat and cholesterol.
• Eating more high-fiber foods like fruits, vegetables, whole grains and soyfoods may help you to lose weight.
Soy Not so Healthy?
According to the Nutrition Committee of the American Heart Association (AHA), recent clinical trials have failed to confirm that soy protein has clinically important favorable effects on cardiovascular health. Additionally, the efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate are not established; evidence from clinical trials is meager and cautionary with regard to a possible adverse effect. For this reason, use of isoflavone supplements in food or pills is now not recommended by the AHA.
Soy products such as fresh or frozen soybeans (edamame), tofu, soy nuts, and some soy burgers can be beneficial to heart health when they displace foods such as hamburgers, cheese and other sources of saturated fat from the diet, however the provide very little advantage of other complete proteins, such as whey, casein, egg and lean poultry sources. Recent clinical trials have shown that consumption of soy protein compared to other proteins, such as those from milk or meat, can lower total and LDL-cholesterol levels however these scientific studies show that 25 grams of soy protein daily in the diet is needed to show a significant cholesterol lowering effect.
Things to consider when choosing soy as a protein source:
• Soy contains a group of protease inhibitors that can inhibit the digestion of protein by interfering with the activity of two important enzymes, trypsin and chymotrypsin. Protease inhibitors interfere with cell communication, protein metabolism and cell growth and may inhibit normal growth and repair functions in children. At first the soy industry claimed that these inhibitors were destroyed by cooking, but that has been disproved. Protease inhibitors have been shown to survive cooking and processing to a small but significant degree Certainly significant for a small child. On a good note, this action may produce an anti-cancer effect in humans by interfering with the growth and spread (metastisis) of tumors.
• Soy has high concentrations of certain chemicals that combine with essential minerals to deposit insoluble salts difficult for your kidneys to eliminate.
• Excessive soy consumption may inhibit brain repair functions. A study with Japanese-Americans found a disturbing correlation between soy consumption and cognitive impairment (refer to:[v] 2. White LR, Petrovitch H, Ross GW, Masaki KH, Hardman J, Nelson J, Davis D, Markesbery W, Brain aging and midlife tofu consumption. J Am Coll Nutr 2000 Apr;19(2):242-55).
• There are studies that suggest a causal relationship between soy phytoestrogens and early puberty in girls and delayed physical maturation in boys.
• Two components of soybeans (eg genistein and daidzein) have estrogen-like activity in humans and animals, which is not necessarily a good thing, especially for prepay women and the fetus. (refer to: Soy Infant Formula Could Be Harmful to Infants: Groups Want it Pulled. Nutrition Week, Dec 10, 1999;29(46):1-2). A study published in the British medical journal, Lancet found that infants fed soy formula had levels of phytoestrogens that were 13000-22000 times higher than natural estrogen concentrations in early life. High doses of the phytoestrogens genistein and daidzein have also been found to interfere with thyroid function and while this would have no effect on a person eating a varied diet, those using soy as their primary source of protein may suffer, even to the point of thyroid disease.
Bottom Line on Soy and Health:
Eaten in moderation soy’s benefits, especially if replacing meat that is high in saturated fats, probably outweigh the risks, however, care should be employed by sensitive populations (pregnant women, children, etc.) when choosing soy as a staple in the diet.