The use of soy in the diet dates back to the Chinese Emperor Shen Nung in 2838 BC. Tofu (a protein-rich curd made from a hot water extract of soybeans) was developed in China and was introduced by Buddhist missionaries to Japan and Korea between the 2nd and 7th centuries. Tofu was even a revered food of the Chinese Emperors in the Ming to Chin dynasties.
Soybeans have been a staple in the diet of Southeast Asians for several centuries. It is estimated that the protein from soy foods comprises 20%-60% of their daily protein. Several studies suggest that Asian populations have lower incidences of cancer, heart disease and osteoporosis than do those of us living in the West. The high concentration of soy foods present in the diet is one factor thought to explain these findings.
Currently, there are a host of soy products found in most grocery stores and even some unusual ones found in natural foods stores. These include dried soybeans, soy oil, soymilk, soy flour, roasted soy nuts, tofu, tofu pate, tempeh, miso, soy sauce, natto, edamame, soy ice cream, soy cheese, soy candy bars, soy burgers and soy hot dogs, and probably a few I've forgotten or even hope not to run across (example: soy marshmallows). Soy milks and tofu are perhaps the most familiar soy foods to those of us who live in the West.
Soybeans are noteworthy for their high protein content, approximately 38%. They also contain 18% fat, primarily polyunsaturated fats and only a small amount of saturated fats. 13% of the soybean is made up of soluble carbohydrates (sucrose, stachyrose, raffinose, and others), 15% insoluble carbohydrates (dietary fiber), and 14% moisture, ash, and miscellaneous compounds.
So, when it comes to a well-balanced food, with good fats, high protein, and fiber, soy is a very attractive choice.
Many common vitamin and mineral nutrients are also found in soy, including iron, zinc, copper, magnesium, niacin, Vitamin B6 and folic acid. Many soy foods are also good sources of calcium. Not only does one half cup of cooked soybeans provide 88 mg of calcium, many brands of tofu are made using calcium sulfate as a coagulant and can contain between 120mg and 750 mg of calcium per ½ cup of tofu. Many soy milks are now also fortified with calcium; some contain 80 mg of calcium per cup but others as much as 300 mg of calcium per serving.
Perhaps the most well known compounds found in soy are the phytoestrogens. Phytoestrogens are plant compounds that have a molecular structure that is similar to, but not the same as estrogen, the main female hormone. Soybeans contain particular phytoestrogens called isoflavones. These isoflavones, because they have a similar structure to estrogen, are able to bind to estrogen receptors in the uterus, breast, brain, bone, arteries, etc. In some cases, they behave in a way that enables them to weakly mimic the effects of estrogen in some tissues, and in other situations, they are able to block the effect of estrogens. When it acts in a weak estrogen-like manner and where it is a weak estrogen blocker is complicated and not yet fully understood. Effects may vary depending on whether the woman is pre- or postmenopausal, whether she is on estrogen replacement therapy or not, other medications, nutritional influences, intestinal health, genetics and more.
There have been some controversies about soy, and in my opinion, most of the concerns have been exaggerated. Some have pointed out problems with thyroid function, inhibition of mineral and protein absorption, and concerns about hormonal effects. For the most part and in most individuals, soy foods will not interfere with thyroid function, will not compromise protein digestion, will not produce consequences in the uptake of minerals and will actually reduce the risk of hormone dependent cancers, not increase it. These problems are not likely to occur with 1-2 servings of soy foods daily, adequate iodine in the diet, using soy in the context of a healthy varied diet, and focusing on organic sources of soy.
Soy foods that are made from organically grown soybeans further enhance the health impact of the individual and the world we live in, because they are grown without pesticides or genetically modified seeds. This is an important issue for soy foods in particular, as genetically modified soy crops have increasingly dominated in the agriculture business. Fortunately, there are farmers and manufacturers who are committed to raising and producing organic soy products.