Soy protein comes from soybeans and offers multiple health benefits, some of which are just beginning to be discovered. This column reviews the health benefits of soy products with a special focus on women and children's health. To date, little has been written or researched that is directly related to perinatal health. Thus, the column has a more broad focus so that childbirth educators have a general resource to gain knowledge related to the use of soy-based foods.
Keywords: soy protein, soy products, perinatal health
Soy protein has received increased attention in recent years among consumers, researchers, and the media. A report released in 1995 estimated that over 12,000 food products were available that contained soy protein (Anderson, Johnstone, & Cook-Newell, 1995 ), and sales of soy beverages rose more than 82% in 1999 (Nestle, 2002 ). A recent study from Europe found that individuals with a habitually health-conscious lifestyle (e.g. individuals who did not eat meat, but did eat fish, or were vegetarians or vegans) were more likely to consume soy foods than the average person (Keinan-Boker et al. 2002 ). The sample included 35,955 persons, from ages 35–74 years, who completed a 24-hour dietary recall interview. From this sample, 195 men and 486 women reported consuming soy products in the last 24 hours.
The purpose of this column is to review the benefits of soy protein and to discuss what populations are likely to benefit from an intake of soy protein. Very little information is available regarding the use of soy protein foods during pregnancy, postpartum, or infancy. Therefore, this column offers a more broad nutritional focus on soy protein with relevant information related to perinatal health interspersed throughout.
Soy protein refers to the protein that is found in soybeans that is often used to replace animal proteins in an individual's diet. The soybean is a legume that contains no cholesterol and is low in saturated fat (Lindsay & Claywell, 1998 ). Soybeans are the only vegetable food that contains all eight essential amino acids (Dudek, 2001 ; Morrison & Hark, 1999 ). Soybeans are also a good source of fiber, iron, calcium, zinc, and B vitamins (Lindsay & Claywell, 1998 ).
Benefits of Soy for Health Promotion
Obesity and Diabetes
Phytoestrogens are currently being researched to determine their usefulness in acting like synthetic estrogen to protect women from bone loss and maintain a healthy heart (Wardlaw, 2000 ). Soy protein has been found to positively influence bone and calcium balance in postmenopausal women (Arjmandi et al. 2003 ). Results were especially significant
for women who were not receiving hormone replacement therapy. These same results were not seen in young, healthy women who were still menstruating (Anderson et al. 2002 ).
Benefits of Soy for Special Populations
Vegetarians and Vegans
Vegetarians are individuals who, for various reasons, do not eat meat. Vegans, in comparison, are individuals who do not eat any products from animals, including eggs, milk, and cheese. Vitamin B12 is only found in animal products and, therefore, may be lacking in the diet of vegans. Use of soymilk is one way to obtain this essential vitamin (Dudek, 2001 ). Cereals and meat substitutes are other options.
Infants with Special Conditions
Infants born with lactase deficiency or galactosemia benefit from the use of soy-based formulas (Dudek, 2001 ). Parents who wish to put their newborn on a vegetarian diet may choose to use a soy-based formula. In addition, infants who are recovering from episodes of diarrhea (and are normally given breast-milk substitutes) may have soy formula recommended to facilitate their recovery. Soy-based breast milk substitutes (formulas) include Prosobee (Mead Johnson) and Isomil (Ross). While soy-based formulas meet an infant's growth and development needs, they do not offer any advantage over milk-based formulas (Whitney & Rolfes, 2002 ).
Infants who are not able to tolerate lactose formulas (those based on cow's milk, casein/whey-based formulas; e.g. Similac, Enfamil, Carnation) may be prescribed soy-based formulas if they are not breastfed (Wardlaw, 2000 ). Each year, about 20%–25% of infants are converted to soy protein formulas (American Dietetic Association and Dieticians of Canada [ADA], 2000 ). The development of lactose-free cow's milk protein-based formulas has made it unnecessary to switch infants to soy-based formula (ADA, 2000), though the practice is still common. The use of soy-based formula is effective in only about 20%–50% of infants because the soy protein eventually triggers a reaction in susceptible infants (Wardlaw, 2000 ). In this instance, predigested protein formulas can be used (e.g. Nutramigen, Alimentum). According to the ADA (2000). soy-based formulas are not recommended for preterm infants weighing less than 1,000 grams and for infants with low birth weightas a means for preventing or managing colic or gastroenteritis.
In a recent study, ingesting soy-based formula or soymilk was associated with peanut allergy in a geographically diverse sample of 13,971 preschool children (Lack, Fox, Northstone, Golding, & the Avon Longitudinal Study of Parents and Children Study Team, 2003 ). The authors proposed that the association of peanut allergy with the intake of soy products could be related to cross-sensitization through a common substance (Lack et al. 2003 ). More research is needed in this area.