THE DOWNSIDE OF SOYBEAN CONSUMPTION
by Beatrice Trum Hunter, who is one of America’s foremost food experts and an Honorary Member of NOHA. She is the Food Editor of Consumers’ Research Magazine and the author of many books on food issues, including Food Additives and Federal Policy: The Mirage of Safety; The Great Nutrition Robbery; and her classic Natural Foods Cookbook.
Soy consumption is being promoted vigorously. Despite many alleged benefits, there is a downside, which is being ignored.
The raw soybean contains numerous anti-nutrients. Although processing can reduce them, it does not eliminate them.1 The raw soybean is an anti-coagulant (an agent that prevents blood clotting). The anti-coagulant property is not reversed by vitamin K, which is a highly effective blood-clotting agent. Green leafy vegetables and liver are excellent sources of vitamin K. Many Americans are low in vitamin K. Soy’s anti-coagulant property is attributed to its anti-trypsin activity. Trypsin is a special enzyme needed to digest protein. In addition, trypsin allows vitamin B12 to be assimilated. Thus, by blocking trypsin activity, the soybean, as an anti-trypsin agent, increases the requirements for vitamin B12 and actually creates vitamin B12 deficiency.2
The raw soybean contains other anti-nutrients, including phytic acid (from phytates), which binds and prevents mineral absorption (especially zinc, calcium, and magnesium).3 Phytic acid is present in grains, too. Thus, vegetarians who depend on soybeans and many soy-containing products, as well as phytate-containing grains, are at even higher risk of deficiencies of these minerals.4 Phytates are present in plant foods but not in animal foods.
Hemagglutinins are also anti-nutrients in the raw soybean. These substances have an ability to agglutinate (clump together) the red blood cells in humans and in other animal species, and significantly suppress growth. These anti-nutrients are known also as "phytoagglutinins" or "lectins."5
These various anti-nutrients present in the raw soybean can be reduced somewhat by proper heat treatment or by sprouting. However, the substances will still be present, albeit at lower levels. The only satisfactory method known at present to deactivate these anti-nutrients is by use of traditional fermentation. This process involves a slow chemical change, triggered by bacteria, molds, and yeast. Fermentation deactivates the enzyme inhibitors, trypsin inhibitor, phytic acid, hemagglutinins, and vitamin antagonists present in raw soybeans. The fermentation process renders the nutrients in soybeans more available and digestible.
Unfortunately, the fermentation process is used with only a few soybean products, and ones that are not especially familiar in the American cuisine, nor readily available. The main fermented soybean products are tempeh (a soybean-based entree), miso (a soybean paste used in soups and sauces), and natto (fermented whole soybeans). Tempeh and miso are available in many health/natural food stores in the United States. Natto, common in Japan, is unfamiliar and unavailable to most Americans. Natto is reported to have a strong odor, a sticky texture, and generally is not favored by novices. Because miso is used merely as a flavoring, the sole fermented soybean food that is an acceptable dish is tempeh.
Contrary to popular notions, soybean products such as tofu and bean curd—familiar and available to Americans—are not fermented. Rather they are processed by precipitation. This method deactivates some but not all of the anti-enzyme agents, and deactivates only a little of the phytates.
Soybeans, even processed ones, have anti-thyroid properties.6 The estrogenic isoflavones (particular plant pigments) in soy—genistein and daidzein—are much touted for their health benefits. What is unpublicized is that they are anti-thyroid agents. Individuals who consume soybean products habitually (the recommendation currently in vogue) may encounter long-range thyroid disturbances. Animal studies relate the isoflavones in soy to thyroid disorders, including goiter. Other studies relate soybean consumption not only to hypothyroidism, but also to low energy levels, poor mineral absorption, and infertility.7
Even at exceedingly low levels, hormones can exert profound biological effects, either beneficial or detrimental. The estrogenic isoflavones in soy are being promoted enthusiastically as health promoters. Although they appear to prevent breast cancer if supplied early, they may promote breast cancer at a later stage in life. Both human and animal studies suggest that soy may increase the risk of breast cancer.8,9,10,11
Frequently, studies are cited of the low breast cancer rate of Asian women who consume soy. However, confounding dietary factors must be considered. Asian women who forsake their traditional diets and embrace the Western diet increase their risk of breast cancer. Soy cannot be singled out as the sole factor.
How beneficial are soy products being offered to Americans? The anti-nutrients in modern soy products, including soy flour, can inhibit animal growth. In humans, they can cause intestinal problems, reduce protein digestion, and lead to chronic deficiencies in the uptake of amino acids.12,13
Soy contains a high amount of fatty acids, which turn rancid rapidly when the soybean is converted into soy flour. Full-fat soy flour is especially prone to such deterioration, and has a disagreeable taste that is difficult to mask. Rancid foods are toxic, and should be avoided.
Textured soy protein, an inexpensive filler, became popular at one time as a hamburger extender. Presently, it is used extensively in processed foods, despite the fact that it contains anti-nutrients.
Protein isolates from soy are used in powder mixes intended for meal-replacement drinks.14 These isolates are obtained by means of a high-temperature process that denatures the protein extensively. In its damaged form, the protein is rendered low in nutritional value. Soy protein (and other protein isolates) cause negative calcium balance in humans and other animals and can contribute to the development of osteoporosis. The soy protein isolates are still high in mineral-blocking phytates, thyroid-depressing phytoestrogens, and potent enzyme inhibitors.15 Also, the high heat used in processing the isolates has been reported to increase the likelihood of forming carcinogenic compounds.16,17
Soy "milk" is used as a cow’s milk replacer, and is marketed for the general population.18 Also, it is used as a substitute for cow’s milk in infant feeding formulas intended for babies who are allergic to cow’s milk. Soy milk is not the equivalent of milk from humans (or from cows, goats, or sheep). Soy milk has several undesirable features when used in infant feeding formulas.19 Soy can exert adverse effects on the hormonal development of infants.20,21,22 Soy milk formula is devoid of cholesterol, a vital substance for proper development of the brain and central nervous system in infants. A study of infants fed soy formula showed a concentration of estrogenic compounds as much as 22,000 times higher than those in human breast milk or in milk-based formula. This startling finding caused speculation in the New Zealand Medical Journal that such an overload of estrogen in infants might result in precocious development of breast and secondary sex characteristics in very young females. In addition, it raised concerns that such an overload might result in male organs not developing normally at puberty.23,24
Soybean oil is likely to be partially hydrogenated. This processing results in the formation of undesirable, unhealthy trans fatty acids in the oil, and in food products made with soybean oil. To date, the vital information about trans fatty acids is not included in the "Nutrition Facts" panel of food labels. Soybean oil, as well as other soybean fractions, also may be from genetically altered soybeans.
Frequently, the soybean has been touted as a "complete" protein from a plant-derived food. Although the soybean may have a better nutritional profile than other beans, still it is low in some essential amino acids. Thus, it is an unbalanced, incomplete source of protein. Only when beans, including soybeans, are supplemented with some complete and balanced protein from an animal-derived food, can the combination achieve the status of being a complete protein food, with all essential amino acids present, and in a good state of balance.
At present, soy is among the major food allergens in the American diet. Individuals of all ages have developed soy allergies, attributable to the proliferation of soy and soy constituents in many commercially formulated products. Since the Food and Drug Administration (FDA) approved a health claim for soy25, more than another thousand new soy-containing products are predicted to flood the marketplace, in addition to the existing plethora. Infants fed soy milk formulas in order to avoid cow’s milk allergy, frequently develop allergy to soy. As soy is promoted aggressively and is available in increasing numbers of food and beverage products, the numbers of soy-allergic individuals are likely to increase, from lifetime over-consumption.
It is difficult to avoid soy and soy constituents unless one chooses basic foods and avoids processed ones. Even then, some soy gets into the diet, indirectly, from soy constituents in the feed of farm animal and farmed fish (in aquaculture).
The soy health claim now permitted is based on 25 grams of soy protein daily, alleged to reduce the risk of heart disease.25 Such a daily overload of soy inevitably increases the risk for soy allergenicity. The FDA determined that diets with four daily servings of soy protein can reduce levels of low-density lipoproteins (LDLs). Four daily servings of soy protein will promote the risk of more allergenic reactions. Also, they replace high-quality protein foods that have no anti-nutrients, with low-quality protein foods that have many anti-nutrients. In addition, the recommendation narrows the food base and negates the sound principle of choosing from as wide a variety of foods as possible.
FDA’s approval of the health claim for soy protein was in response to a petition by a leading soy producer. The soybean lobby exerts powerful clout. In addition, food and beverage processors favor soybean use because it is a low-cost filler, extender, and replacer in foods for humans and in feed for animal. It is a cost cutter that swells profits.
In view of the overall evidence against soy, is the health claim justified? Previous health claims have been approved in response to commercial interests and similarly based on highly selective evidence. One critic, Tom Valentine, observed in True Health that "no other dietary staple has so many anti-nutrient drawbacks as soy. Conversely, no other food has so many public relations firms and lobbyists working for it."
Despite the present popularity of the soybean, it is being threatened by a rival—mycoprotein. Single cell proteins, derived from bacteria, yeast, or fungi, are inexpensive meat alternatives. Mycoprotein, approved in many other countries, has been under FDA scrutiny for years. Now, the agency appears poised to approve its use in food and feed. Like the soybean, mycoprotein is touted for its functional, nutritional, and chemical benefits. Its imminent approval may launch a new food revolution. It is truly a new food constituent and will transfer food from being grown on the land to being produced in the laboratory. The soybean may be toppled.
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2Lepkovsky, S., "Antivitamins in Foods," Chapter 11 in Toxicants Occurring Naturally in Foods, Publication 1354: 98-104, National Academy of Sciences/National Research Council, Washington, DC, 1966.
3Tait, S., et al, "The availability of minerals in food, with particular reference to iron," Journal of Research in Society & Health, 103(2):74-7, April 1983.
4Sandstrom, B., et al, "Effects of protein level and protein source in zinc absorption in humans," Journal of Nutrition, 119: 48-53, January 1989.
5Liener, I. E., "Hemagglutinins in Foods," Chapter 6 in Toxicants Occurring Naturally in Foods, Publication 1354: 51-7, National Academy of Sciences/National Research Council, Washington, DC, 1966.
6Ikeda, T., et al, "Dramatic synergism between excess soybean intake and iodine deficiency on the development of rat thyroid hyperplasia," Carcinogenesis, 4: 707-13, April 21, 2000.
7Divi, R. L., et al, "Anti-thyroid isoflavones from soybean," Biochemical Pharmacology, 54: 1087-96, November 15, 1997.
8Hilakivi-Clarke, L., et al, "Maternal genistein exposure mimics the effects of estrogen in mammary gland development in female mouse offspring," Oncology Report, 5(3): 609-16, May-June 1998.
9Hilakivi-Clarke, L., et al, "Maternal exposure to genistein during pregnancy increases carcinogenic-induced mammary tumorigenisis in female rat offspring," Oncology Report, 6:1089-95, September-October 1999.
10Matone, G., et al, "Effects of genistein on growth and development of the male mouse," Journal of Nutrition, 86: 235-40, 1956.
11Petrakis, N. L., et al, "Stimulatory influence of soy protein isolate on breast secretion in pre- and post-menopausal women," Cancer Epidemiology and Biological Previews, 5: 785-94, 1996.
12McGuinness, J., et al, "The effects of long-term feeding of soya flour on the rat pancreas," Scandinavian Journal of Gastroenterology, 15: 497-502, 1980.
13Murphy, P. A., "Phytoestrogen content of processed soybean foods," Food Technology, 36: 50-4, 1982.
14Torum, B., "Nutritional quality of soybean protein isolates studies in children of preschool age," Chapter in Soy Protein and Human Nutrition, Harold L. Wicke, et al, (eds.), Academic Press, New York, 1979.
15Stob, M., "Estrogens in Foods," Chapter 2 in Toxicants Occurring Naturally in Foods, Publication 1354: 18-23, National Academy of Sciences/National Research Council, Washington, DC, 1966.
16Constantinou, A., "Interaction between genistein and estrogen receptors may enhance mammary tumor growth," American Association for Cancer Research, April 2000, reported in "The Power of Soy," Guterman, L., Today’s Chemist at Work (publication of the American Chemical Society), June 2000, page 47.
17Dees, C., et al, "Dietary estrogens stimulate human breast cells to enter the cell cycle," Environmental Health Perspectives, 105 (Supplement 3): 633-6, 1997.
18Wallace, G. M. "Studies on the processing and properties of soy milk," Journal of Science & Food Agriculture, 22: 526-35, October 1971.
19Fort, P., et al, "Breast and soy-formula feeding in early infants and the prevalence of autoimmune thyroid disease in children," Journal of the American College of Nutrition, 9:164-7, September 1990.
20Setchell, K. D. R., et al, "Exposure of infants to phyto-oestrogens from soy-based infant formula," Lancet, 350: 23-7, 1997.
21Setchell, K. D. R., et al, "Isoflavone content of infant formulas and the metabolic fate of these phytoestrogens in early life," American Journal of Clinical Nutrition, 68 (Supplement): 1453S-61S, 1998.
22Setchell, K. D. R., "Phytoestrogens: the biochemistry, physiology, and implications for human health of soy isoflavones," American Journal of Clinical Nutrition, 68 (Supplement): 1333S-46S, 1998.
23Irvine, C., et al, "The potential adverse effect of soybean phytoestrogens in infant feeding," New Zealand Medical Journal, 108: 318, May 24, 1995.
24James, V., "Comments on isoflavones in soy-based infant formulas," Journal of Agricultural Food Chemistry, 46: 3395, 1998; also, Fitzpatrick, M. G., "Comments," 3396-7.
25Food & Drug Administration, "Food labeling; health claims: soy protein and coronary heart disease," FDA 21CFR, Part 101; Docket No. 98P-0683, October 26, 1999Article from NOHA NEWS, Vol. XXVI, No. 4, Fall 2001, page 3.