(graph linked to study) Environmental Health Perspectives Supplements Volume 110, Number 3, June 2002 // Goitrogenic and Estrogenic Activity of Soy Isoflavones // Dr. Daniel R. Doerge and Dr. Daniel M. Sheehan // Division of Biochemical Toxicology, National Center for Toxicological Research, Jefferson, Arkansas. Abstract -- Soy is known to produce estrogenic isoflavones. Here, we briefly review the evidence for binding of isoflavones to the estrogen receptor, in vivo estrogenicity and developmental toxicity, and estrogen developmental carcinogenesis in rats. Genistein, the major soy isoflavone, also has a frank estrogenic effect in women. We then focus on evidence from animal and human studies suggesting a link between soy consumption and goiter, an activity independent of estrogenicity. Iodine deficiency greatly increases soy antithyroid effects, whereas iodine supplementation is protective. Thus, soy effects on the thyroid involve the critical relationship between iodine status and thyroid function. In rats consuming genistein-fortified diets, genistein was measured in the thyroid at levels that produced dose-dependent and significant inactivation of rat and human thyroid peroxidase (TPO) in vitro. Furthermore, rat TPO activity was dose-dependently reduced by up to 80%. Although these effects are clear and reproducible, other measures of thyroid function in vivo (serum levels of triiodothyronine, thyroxine, and thyroid-stimulating hormone ; thyroid weight ; and thyroid histopathology) were all normal. Additional factors appear necessary for soy to cause overt thyroid toxicity. These clearly include iodine deficiency but may also include additional soy components, other defects of hormone synthesis, or additional goitrogenic dietary factors. Although safety testing of natural products, including soy products, is not required, the possibility that widely consumed soy products may cause harm in the human population via either or both estrogenic and goitrogenic activities is of concern. Rigorous, high-quality experimental and human research into soy toxicity is the best way to address these concerns. Similar studies in wildlife populations are also appropriate.
The below is taken from Health & Learning Info, A 2 Z of Health, Beuaty, and Fitness -- an online magazine:
What Does the Thyroid Do? "The thyroid’s main job is to produce thyroid hormone. Hormones are chemicals that are secreted by glands which act like messengers telling specific body parts what to do. Thyroid hormones help the body make energy, keep body temperature regulated and assist other organs in their function. The thyroid produces two major hormones: triiodothyronine and thyroxine, commonly referred to as T3 and T4. (The “3” and the “4” relate directly to the amount of iodine molecules which are used to create these hormones.)" .... "Soy contains goitrogens, plant chemicals that inhibit thyroid function. And 99% percent of the soy we consume is genetically modified, otherwise known as GMO. Soy has one of the highest percentages of contamination by pesticides of any of our foods. Soy is rich in phytic acid, a chemical that blocks the uptake of essential minerals. Soy has the highest phytate levels of all the grains and legumes. The phytates have been found to be resistant even to long slow cooking in an effort to denature them. There exist hundreds of research articles on phytic acid and their effects, including binding with certain nutrients like iron to inhibit their absorption."
CNN.com: Health, Diet & Fitness
White, for one, worries that soy may speed the aging of brain cells. He recently found evidence that the brains of elderly people who ate tofu at least twice a week for 30 years were aging faster than normal. Tests designed to assess memory and analytical ability showed that their brains functioned as if they were four years older than their actual age, White says of his study published in the April 2000 issue of the Journal of the American College of Nutrition.
Another fear is that the estrogen-like substances in soy may dampen the function of the thyroid. Consuming 40 milligrams of isoflavones a day can slow the production of thyroid hormone, says Dr. Larrian Gillespie, author of "The Menopause Diet" and "The Goddess Diet." (One tablespoon of soy powder contains about 25 milligrams of isoflavones, while most isoflavone supplements come in 40-milligram pills.)
According to Gillespie, within a few weeks of regularly consuming 40 milligrams of isoflavones, some women feel fatigued, constipated and achy all over. Some also gain weight and have heavier menstrual periods. Menopausal women are at particular risk, since they're already prone to hypothyroidism. "Women think it's because of hormones and don't realize they're symptoms of hypothyroidism," Gillespie says. "Once they stop the soy, they say, 'I'm feeling fine again.' " ...
....Messina, for instance, recommends a daily serving of soy: perhaps 1 cup of soy milk or 3 to 4 ounces of tofu.
So, how much soy did Asians eat?
Not much, even though we, as a society have been led by expert mass marketing to think otherwise. Soy has never, ever been a food staple in Asian history. The exception was that the poor often used the soybean to fill their empty bellies during times of famine. Even then, the soybeans were prepared in such a way as to neutralize the natural and inherent soy toxins thus proving that even ancient Asians understood the soybean better than we do today.
To consume a serving of tofu and a couple of glasses of soy milk has become commonplace for many Americans. Soy is also touted as the original protein source for those perusing a vegetarian lifestyle.
This is absolutely in excess of the amount of soy that Asians consume. In native Asia, from where so much of this "research" is purported to have originated, a tablespoon or two of soy is simply used as a condiment. According to K. C. Chang, the editor of Food in Chinese Culture, the total caloric intake of soy in the Chinese diet during the 1930's was only 1.5 percent as compared to 65 percent for pork products.
The huge concern about consuming large amounts of soy products lies in the mega dosing of isoflavones. If consumers follow the nutritional advice of Protein Technologies International (manufacturers of soy-isolated protein) their daily genistein intake (an isoflavin found in soy) could exceed 200 milligrams per day. It goes without saying this level of genistein intake should be avoided.
Up until only two decades ago, soy was considered unfit to eat. By Asians, mind you! To see the hold soy products have on the USA marketplace is truly a miracle. Agricultural literature clearly depicts the soybean and its first and foremost use as a crop rotation plant used to fix nitrogen in the soil. Soybeans did not serve as any form of food until the advent of the Chow Dynasty. During this period, fermentation techniques brought us some of the soy edibles we see today, such as tempeh, soy sauce and natto. In the second century B.C., the Chinese discovered a porridge of cooked soybeans could be precipitated with calcium sulphate or magnesium sulphate (Plaster of Paris or Epsom salts) to make tofu. Sound healthy?
The Chinese did not eat unfermented soybeans as they did other legumes because the soybean contains large amounts of antinutrients (toxins). First among them is hemagglutinin, a clot promoting substance that makes red blood cells clump together. Soy is rich in enzyme inhibitors that block the action of much needed enzymes required to digest proteins. These inhibitors are not deactivated during cooking. They can cause gastric distress and chronic deficiencies in amino acid uptake. Protein inhibitors and hemagglutinin are scientifically proven to inhibit growth, as evidenced in studies of weanling rats that eventually failed to thrive.
Soy contains goitrogens, plant chemicals that inhibit thyroid function. And 99% percent of the soy we consume is genetically modified, otherwise known as GMO. Soy has one of the highest percentages of contamination by pesticides of any of our foods. Soy is rich in phytic acid, a chemical that blocks the uptake of essential minerals. Soy has the highest phytate levels of all the grains and legumes. The phytates have been found to be resistant even to long slow cooking in an effort to denature them. There exist hundreds of research articles on phytic acid and their effects, including binding with certain nutrients like iron to inhibit their absorption.
The marketing push for more soy products has been relentless and global. Public relations firms help convert research projects into newspaper articles and advertising copy. It has worked like a charm. Soy protein is now found in a majority of supermarket breads. Soy can be found blended in the regular old corn tortilla. Try to find a salad dressing in a health food store whose first ingredient is not soy oil. Advertising for a new soy enriched loaf from Allied Bakeries in Britain targets menopausal women seeking relief from hot flashes. It goes on and on.
For more information on the great soy misinformation please consult the well-written and respected book entitled The Whole Soy Story by Dr. Kaayla Daniel.
About The Author:
Dr. Linda Posh MS SLP ND brings a fresh perspective to natural health and nutrition. She packs a solid educational background with degrees in organic chemistry, psychology and a Masters in Communication Sciences and Disorders. Visit www.Nutra-Resources.com for information.
