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Soy: The Pendulum Swings the Other Way

Soy foods have become a regular staple in health food stores, and articles promoting it as a superfood that belongs prominently in every diet are plentiful. After the Food and Drug Administration approved food labeling that stated 25 grams of soy protein along with a low cholesterol and low saturated fat diet could reduce the risk of heart disease, the soy bandwagon got quite crowded. Articles demonstrating longevity among Chinese and Japanese due in good part to soy in their diets were cited as a reason to increase consumption of soy protein. The tide has turned however, and many adverse effects of soy have been found which actually encourage limiting the amount of soy you should include in your diet.

Without going back too far into history, soybeans weren't used as food until they were fermented. Eating them raw can be poisonous, and unfermented soybeans actually block the action of the essential enzyme trypsin and other enzymes that are necessary for protein digestion. That said, tofu, a puree of cooked soybeans combined with calcium or magnesium sulfate to make a bean curd dates back the second century B.C.. An increase in the number of vegetarians in recent years has also spurred soy use as an alternate and "healthy" source of protein to replace meat, fish and eggs.

So where has thinking changed along the way? One is the myth that soy is a natural product. Most soy in the United States is genetically modified and subject to crop spraying with pesticides and herbicides. Another is the aforementioned FDA dictate of soy as a protection against heart disease. The American Heart Association Science advisory paper reviewed studies and clinical trials and found it took almost half the amount of daily protein consumed as soy to make an average of 3% reduction in LDL cholesterol, not a significant outcome.

Soybeans are known goitrogens. Goitrogens block the uptake of iodine in the thyroid gland, iodine being the building block for thyroid hormone. As such, glands enlarge and become less efficient and eventually thyroid hormone levels are suppressed. As thyroid is necessary for metabolism, a hypothyroid state can ensue as gland size grows.

Soy isoflavones mimic the effect of estrogen, and as such soy products for years have been promoted as beneficial in reducing menopausal symptoms in females. Soy intake is helpful in this regard, but obviously its effects in males are unwanted as testosterone levels decrease and some physical feminization can occur. Soy's effect on cancers such as breast cancer, prostate cancer and colorectal cancer have been contradicting, and there is no clear evidence that soy reduces the risks in each of these situations.

In other situations where soy products have been advocated, newer studies have not shown it to be advantageous. Vegetarians who rely on soy to replace meat and dairy products often need calcium, magnesium and zinc supplements, and menstruating women very often require additional iron supplementation. Soy in female children provides isoflavones (plant estrogens, in effect) to raise their levels above normal and sometimes induce early puberty. Too much estrogen-like substance in newborns (often given soy formula in place of milk) can negatively influence proper hormone balance in growing babies and children. The American Academy of Pediatrics only advocates soy formula for those with a preference for vegetarian diet for their children and in those with hereditary lactase deficiency, and doesn't feel studies confirm that colicky babies necessarily do better when soy formula is substituted.

So does this mean completely abandoning soy because it is potentially dangerous and not beneficial? A lot of the literature is controversial as to its benefits and risks. The studies are particularly tough because everyone metabolizes soy differently, so there's no standard amount that can be tested uniformly. Soy foods in the diet are generally not harmful, especially as an added substance in the body and not a full replacement of animal and dairy sources of protein. However, soy in larger amounts does have its dangers, and resulting vitamin and mineral deficiencies in a soy-based diet as well as the effect on the endocrine system (thyroid hormone and estrogen) have to be monitored and supervised by a physician to ensure good overall health.

Authored by Dr. Bob Goldstone, M.D.

The information contained on this page is not intended to provide medical advice, which should be obtained directly from your physician.