Soy milk (also called soymilk, soya milk, soybean milk, soy bean milk, soy drink, or soy beverage) is a milk-like beverage made from soybeans.
Soy milk originated in China, a region where soybean was native and used as food long before the existence of written records. Later on, the soybean and soybean foods were transplanted to Japan. Soybean or “vegetable” milk is reputed to have been discovered and developed by Liu An of the Han Dynasty in China about 164 B.C. Liu An is also credited with the development of “Doufu” (soybean curd) in China which 900 years later spread to Japan where it is known as “tofu”.
Traditional soy milk, a stable emulsion of oil, water and protein, is simply an aqueous extract of whole soybeans. The liquid is produced by soaking dry soybeans, and grinding them with water. Soy milk contains about the same proportion of protein as cow’s milk~ around 3.5%; also 2% fat, 2.9% carbohydrate and 0.5% ash.
Nutritional Value of Soymilk
Plain, unfortified soymilk is an excellent source of high-quality protein, B-vitamins and iron. Some brands of soymilk are fortified with vitamins and minerals and are good sources of calcium, vitamin D and vitamin B-12. Soymilk is free of the milk sugar lactose and is a good choice for people who are lactose intolerant. Also, it is a good alternative for those who are allergic to cow’s milk. Children can enjoy homemade or commercially prepared soymilk after the age of 1 year. Infants under 1 year of age should be fed breast milk, commercially prepared infant formula or commercial soymilk infant formula.
Nutrients in 8 ounces of plain soymilk:
|Regular Soymilk||Lite Soymilk (reduced fat)|
Soy vs cow milk
Strictly speaking, soy ‘milk’ is not a milk at all – it is soy juice. It is largely promoted on the basis that it does not contain animal fat or lactose, it is of plant origin, and it contains components such as phytoestrogens which are suggested to be beneficial to health.
Soy protein is of relatively high quality (provided a powerful inhibitor of protein digestion is removed during processing), but its profile of essential amino acids is inferior to that of cows milk. In particular, the value of its protein is limited by its low level of sulphur amino acids. Soy beverage is naturally quite low in calcium (although some brands are fortified) and it contains phytate, a strong inhibitor of the absorption of several minerals, including iron (Hurrell, 1992; Reddy, 1996), zinc (Lonnerdal, 1994) and calcium (BNF, 1989; Heaney, 2000). An additional influence of soy protein on mineral bioavailability cannot be ruled out (Cook, 1981). In this context, concern has been expressed about the calcium status of children reliant on soy-based beverages and the impact of this on their bone health.
Claims for anticancer effects of phytoestrogens are based largely on epidemiological evidence suggesting that Asian populations traditionally consuming soy foods have lower rates of hormone-dependent and certain other cancers than populations consuming little or no soy (reviewed by Anderson, 1999). Despite the observed epidemiological associations, Anderson (1999) points out that the data from in vitro and in vivo studies are highly contradictory; some studies have indicated protective effects of soy or isoflavones against chemically-induced breast and colonic neoplasms; others have not. In particular, he cites research showing that isoflavones enhance the proliferation of human MCF-7 breast cancer cells in vitro , and that dietary genistein promotes the growth of MCF-7 cell tumors in vivo. Soy intervention studies in humans have shown that short- or long-term soy consumption has a stimulatory (i.e., oestrogenic) effect on the premenopausal female breast, as evidenced by epithelial cell proliferation, increased secretion of breast fluid, and elevated levels of plasma oestradiol. This is the opposite of what would be expected of soy isoflavones and could represent a cancer-promoting effect. Anderson (1999) discusses the range and complexity of the mechanisms by which phytoestrogens may either inhibit or promote cancer cell proliferation, some related to oestrogen agonist/antagonist effects, others unrelated to sex hormones. A consensus is emerging in the field that outcomes are unpredictable, with the possibility of both adverse and beneficial effects occurring in the same individual in different target organs, depending on the stage of the life cycle.
Misconceptions about the prevalence of lactose intolerance and allergies have led to increasing use of soy protein-based infant formulas. Although soy formulas offer no real advantage over cows milk formulas vis-à-vis colic or atopic disease, they are increasingly chosen as an alternative for vegan parents and for most infants with documented allergies (or fear of allergies) to cows milk protein. Yet a critical assessment shows that a substantial proportion of babies who develop allergy to milk proteins will also be allergic to soy-based formulas (Host, 1997). Furthermore, long-term studies have shown that atopic disease is no less common in children given soy formula (Kjellman, 1979; Miskelly, 1988; Burr, 1993), since infants susceptible to allergy tend to react to the first foreign protein to which they are exposed. The only reliable alternative formulas are based on fully hydrolyzed milk protein (Hide, 1994). The American Academy of Pediatrics does not recommend soy-based formula because of the risk of juvenile diabetes associated with it.
Structurally similar to estrogen, phytoestrogens common in soy-based formulas bind to estrogen receptors and partially promote and inhibit estrogenic activity. Although infants are able to digest, absorb and excrete these isoflavones as efficiently as adults, it remains unclear whether they are beneficial or detrimental to health. In a study done in the UK, it was estimated that a one- to two-month-old infant would consume approximately 5 mg isoflavone/kg body weight per day, whereas a four- to six-month-old infant would consume slightly less: approximately 4.5mg isoflavone/kg body weight per day. Consider this: per unit of body weight, the infant’s potential intake of phytoestrogens from isolated soy protein-based formula is higher than the amount demonstrated to influence a woman’s menstrual cycle. Also, phytoestrogens have demonstrated reproductive and developmental toxicity in livestock and experimental animals. In contrast, the isoflavone content of breast milk or cows milk is negligible.