Soya

Soya

It's What's for Dinner

Alison Solomon and Jennifer Baker

Dietary Sources:

Soya comes from the soya bean pods that are located in the soya plant. The scientific name is Glycin Max and it is from the Pea family (Fabaceae). Soya bean pods were first cultivated in China over 4000 years ago. Today, they are mostly cultivated in North and South America inaddition to China.

Beneficial effects:

A. Soya beans contain antioxidants. These compounds protect cells from damage that is caused by free radicals. These free radicals are believed to be responsible for many cancers and premature aging.

B. Soya beans have cholesterol- lowering properties. They lower LDL (Low-density lipoprotein) and raise HDL (High-density lipoprotein).

C. Soya beans can increase bone mineral density and decrease calcium loss in aging women.

D. Soya beans contain natural plant hormones known as isoflavones. These isoflavones are also called phytoestrogens. The phytoestrogens are similar to the estrogens that our bodies produce naturally. During menopause, the body produces less estrogen. However, phytoestrogens located within the soya bean can be absorbed by the body, and thus mimic estrogen.

Principal Uses:

A. Protection against cancer. Studies have shown that populations that eat a diet rich in soya products suffer less breast, colon endometrial, ovarian, and prostate cancer. This is due to the antioxidant effects of genistein, one active component of soya beans.

B. Protection against risk of heart disease. There is less incidence of coronary heart disease in communities that eat a diet rich in soya beans. This is due to its lowering of the LDL cholesterol level.

C. Protection against bone disease. There is less incidence of osteoporosis in populations that eat a soya-rich diet. This is due to soya's ability to decrease calcium loss and increase bone mineral density.

D. Nature's hormone replacement therapy. Due to the action of the phytoestrogens that are located within the soya bean, there is a lower incidence of menopausal symptoms in women. In Japan, hot flashes are so uncommon that they do not even have a word that describes them.

Available Forms:

There are a wide variety of products made from soya bean. Some examples are:

A. Tofu- soya bean curd made from coagulated soya milk. It is sometimes known as soya cheese. Can be purchased as silken tofu or firm tofu.

B. Textured Vegetable protein- defatted soya flour which has been processed and dried to give a sponge-like texture. It can be flavored to resemble meat. It is usually incorporated into vegetarian burgers, sausages, and canned foods.

C. Tempeh- fermented soya bean paste. It has a chewy texture and can be used as a meat substitute in recipes.

D. Miso- fermented condiment made from soya bean, grain, salt, and water. Used to give flavor to soups, stews, casseroles, and sauces.

E. Soya sauces- fermented soya beans with cracked roasted wheat, salt and water.

F. Soya milk- used as a substitute for dairy milk. It provides a large amount of protein. Most brands add calcium, Vitamin-D2, Vitamine-Bl2, and VitaminB2.

Dosage Ranges:

Western diets usually get 5mg of phytoestrogens a day while the Japanese diet provides 5-20 times that amount. Experts recommend that 40-60mg of soya a day is needed for optimal nutritional therapy. This is equivalent to 120g tofu, 1.3 liters of soymilk, or 35g of soy flour.

Interactions:

There are two principal drug-interactions with soya. The first one is monoamine oxidase inhibitors. Soya products contain tyramine, which can cause a hypertensive reaction in patients currently taking monoamine oxidase inhibitors. Soya foods to avoid are fermented soya bean and soya bean pastes that contain a significant amount of tyramine. Soya products that should be used with caution are soy sauces. The second drug interaction involves L-thyroxine. Soya products decrease the absorption of Lthyroxine in infants with congenital hypothyroidism. This becomes a problem if the infant is receiving soy-based formula. The L-thyroxine dose should be increased if an infant with congenital hypothyroidism is fed soy-formula. After the soy-formula is discontinued, the L-thyroxine dose should be decreased.

Summary of Clinical Trials

Pollard & Luckert Study: The purpose of this study was to examine if eating a diet high in isoflavones has a protective effect on prostate related cancers. Isoflavones contain genistein, which has been speculated to have anticarcinogenic activity. In this experiment, Lobund-Wister rats were studied because they are inherently susceptible to both spontaneous and induced cancers of the prostate and seminal vesicle. The parameters that were monitored were the number of L-W rats that developed the tumors and the length of their latency period. There were two phases of this experiment. In the first phase, 24 L-W rats were fed a high isoflavone diet and 24 L-W rats were fed a low isoflavone diet before initiation of methylnitrosourea. The results were that 8/24 rats on a high isoflavone diet developed tumors with an average latency period of 10 months and 10/24 rats on a low isoflavone diet developed tumors with an average latency period of 7.3 months. In the second phase, 35 L-W rats were fed a high isoflavone diet and 33 LW rats were fed a low isoflavone diet after initiation of methylnitrosourea. The results were that 18/35 rats on a high isoflavone diet developed tumors with average latency period of 10.6 months and 20/33 rats on a low isoflavone diet developed tumors with an average latency period if 9.3 months. They concluded that a high isoflavone diet decreased both the number of rats that developed tumors and the latency period of the tumors.

Kurowska Jordan et al Study: The purpose of this study was to determine if substituting soybeans for cow's milk improves the lipid profile of patients with hypercholesterolemia. 17 men and 17 women with hypercholesterolemia participated in this study. The study was a randomized, three-treatment crossover trial with two-two weeks washout periods. The three periods were the following: four weeks of cow's milk, 4 weeks of cow's milk and soy oil, and 4 weeks of soybean. During the soybean only treatment period, the HDL cholesterol increased a mean 9% and the LDL/HDL ratio decreased a mean 14% as compared to the cow's milk treatment period. They concluded that soybeans increase HDL cholesterol levels as compared to cow's milk. They also conclude that this is due mainly to soy protein because combination of cow's milk and soil oil did not effect HDL cholesterol levels.

References

Bingham, Shelia. "Carcinogens and anticarcinogens in Human Diet" British Medical Journal. 313(7050): 176, 1996 July.

Jabber MA, Larrea J, & Shaw RA. "Abnormal thyroid function tests in infants with congenital hypothyroidism: the influence of soy-based formula." Journal of the American College of Nutrition. 16(3):280-2, 1997 Jun.

Kurowska EM, Jordan J, Spencer JD, et al. "Effects of substituting dietary soybean protein and oil for milk protein and fat in subjects with hypercholesterolemia." Clinical & Investigative Medicine. 20(3): 162-70, 1997 Jun.

Langley, Gill. "Legal decent, honest, truthful." British Medical Journal. 311(7017): 1442, 1995 Nov.

Maclean, William C. "Cow's milk and the diabetes debate." Pediatric. 96(3):5412, 1995 Sept.

Petrakis NL, Barnes S, King EB, et al. "Stimulatory influence of soy protein isolate on breast secretion in pre and postmenopausal women." Cancer Epidemiology, Biomarkers & Prevention. 5(10):785-94, 1996 Oct.

Pollard M & Luckert PH. "Influence of isoflavones in soy protein isolates on the development of induced prostate-related cancers in L-W rats." Nutrition & Cancer. 28(1):41-5, 1997.

Pusztai A, Grant G, Bardocz, et al. "Both free and complexed trypsin inhibitors stimulate pancreatic secretion and change duodenal enzyme levels." American Journal of Physiology. 272(2Ptl):G340-50, 1997 Feb.

Wagner JD, Cefalu WT, Anthony MS, et al. "Dietary soy protein and estrogen replacement therapy improve cardiovascular risk factors and decrease aortic cholesteryl ester content in ovariectomized cynomolgus monkeys." Metabolism: Clinical &; Experimental. 46(6):698-705, 1997 Jun.

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