Frequently Asked Questions
Click on the question regarding soy to learn the answer.
1. What is the historical background of soy?
2. When was soy first introduced in the United States?
3. Is soy protein a nutritionally complete protein?
4. How does soymilk compare with cow’s milk?
5. Does calcium absorption differ between soymilk and cow’s milk intake?
6. Are there any FDA approved health claims about soy?
7. How much soy protein is in soyfoods?
8. What makes soy heart-healthy?
9. Is the soy heart health claim based on a meta-analysis that has since been disproven?
10. How are soybeans processed? Does processing affect the health benefits or safety of soy?
13. Are there any health benefits or risks associated with consuming foods that contain isoflavones?
14. Is there a recommended daily isoflavone intake?
15. Is taking an isoflavone supplement the same as eating soyfoods?
16. Is there any relationship between consumption of soyfoods and breast cancer risk?
17. Does eating soy provide more estrogen than the body can handle?
20. Is it safe for pregnant/lactating women to consume soyfoods?
21. Is it safe for infants to consume soy-based formulas?
22. Is it appropriate for children to consume soymilk?
23. What are protease inhibitors and do they have an adverse effect on growth?
24. Is soy protein an allergen?
25. Do soyfoods impact cognitive function?
26. Does phytic acid, which is found in soy, cause problems with mineral absorption?
27. Can people taking blood-thinning medication consume soyfoods?
Answer to Frequently Asked Questions
1. When did soybeans and soyfoods first appear?
Answer: Chinese historical documents suggest that soybeans have been grown and consumed for many thousands of years. Archeological finds and dating of early Chinese writings indicate that soybeans emerged as a domesticated crop in the eastern half of Northern China during the Chou dynasty (11th to 7th Century BC). The four most important soyfoods are miso, soy sauce, tempeh and tofu. Miso is a fermented soyfood that originated in China, and was modified in Japan where it has remained a staple of the diet for centuries. Soy sauce was a byproduct of miso production, and both were used to flavor foods, just as they are today. Tempeh, which originated in Indonesia, is made by fermenting cooked soybeans with a common mold. Tofu is the curd formed by adding certain salts to soymilk and is not fermented. Learn more about the history of soy.
2. When were soybeans and soyfoods first introduced in the United States?
Answer: In the United States, soybeans were first introduced in Georgia, where Samuel Bowen began planting soybeans on his plantation in the 1760s. He also patented processes to make soy sauce and vermicelli (soy noodles). Almost two hundred and fifty years later, pastas made with soy were introduced into the American marketplace.
Innovations in soyfood processing have created an array of soy-based foods that appeal to infants, children and adults. From 2000 to 2007, food manufacturers in the U.S. introduced over 2,700 new foods with soy as an ingredient, including 161 new products introduced in 2007 alone. The 1999 FDA approved health claim for soy and heart health brought many new introductions, leading to 406 new products in 2001, 278 in 2002, 336 in 2003, 448 in 2004, 291 in 2005, and 471 in 2006, according to the Mintel Global New Products Database. In the United States, soy drinks, tofu, cultured soy, non-meat alternatives, frozen dairy free soy treats, soy nuts, soy nut butter, and/or cereals and bars with soy can be found in most supermarkets. Learn more about the history of soy.
NUTRITIONAL PROPERTIES OF SOY
3. Is soy protein a nutritionally complete protein?
Answer: Yes, soy protein is the only complete plant protein that is equivalent to animal protein. Soyfoods contain all nine essential amino acids in the ratios needed for human growth and health, and they are readily digestible. The USDA, FAO/WHO Expert Consultation on Protein Quality, and the Institute of Medicine, Food and Nutrition Board evaluates protein quality using the Protein Digestibility Corrected Amino Acids Score (PDCAAS) method to determine protein quality. PDCAAS measures the amino acid pattern of proteins and factors in digestibility. According to the PDCAAS system, soy protein and egg whites have a maximum score of 1.0, followed by milk and meat proteins. (1)
4. How does soymilk compare with cow’s milk?
Answer: A number of fortified soymilks on the market today contain nutrients in level’s similar to cow’s milk and are good sources of calcium, vitamin A, riboflavin and phosphorus, as well as many other vitamins and minerals. Most soymilks are fortified with 300-400 milligrams of calcium, 120 IU of vitamin D, 500 mg vitamin A and 3 micrograms vitamin B12 per 8 ounces. These levels of nutrients are equivalent to cow’s milk; however, soymilk contains no cholesterol and is very low in saturated fat. (2) Learn more about soymilk.
5. Does calcium absorption differ between soymilk and cow’s milk?
Answer: No, recent research shows that calcium absorption from calcium-fortified soymilk is the same as that from cow’s milk. (7) Fortified soymilk usually contains more calcium than cow’s milk and is a significant source of calcium in the diets of non-dairy drinkers. Studies have also found that in comparison with animal protein, soy protein decreases calcium excretion, presumably due to the lower sulfur amino acid content of soy protein. Consequently, a soy-based diet allows one to maintain calcium balance with a lower calcium intake. (3 – 7) Learn more about soymilk and calcium.
SOY AND HEART HEALTH
6. Are there any FDA approved health claims about soy?
Answer: Yes, on October 26, 1999, the Food and Drug Administration authorized a health claim that links the consumption of soy protein with a reduced risk of coronary heart disease. The FDA extensively reviewed over 50 scientific research studies and public comments before approving a health claim that recommends “25 grams or 4 servings of foods with 6.25 grams of soy protein daily to lower cholesterol.” (8) Since that time, numerous research studies and evidence based reviews of research on soy protein and LDL cholesterol have confirmed the FDA approved claim. (9 – 16) Learn more about soy and heart disease.
7. How much soy protein is in soyfoods?
Answer: The soy protein content of soyfoods varies from as little as 1-2 grams per serving to 18-20 grams per serving. On average, one can obtain 25 grams of soy protein by consuming three to four servings of soyfoods. Products that carry the FDA authorized health claim on the label must contain at least 6.25 grams of soy protein per serving, but usually contain much more. A wide variety of soyfoods carry the claim, including: regular and seasoned tofu, soymilk and soymilk products such as yogurt and cheese, cereals, meat alternatives, baked goods, soy nut butter, tempeh, soy dairy free frozen desserts, and soy protein bars and powders. (2, 8) Learn more about how much soy protein is in certain soyfoods.
8. What makes soy heart-healthy?
Answer: Soyfoods have many nutritional benefits that can contribute to a heart healthy diet. Soyfoods are low in saturated fat and cholesterol-free. According to a statement from the AHA, “soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, minerals and low content of saturated fat and no cholesterol.” (11,12) The soy protein also has the added benefit of lowering LDL cholesterol and possibly blood pressure (9 – 16). Learn more about soy and heart disease.
9. Is the soy heart health claim based on a meta-analysis that has since been disproven?
Answer: No, FDA conducted thorough scientific analysis of 27 separate studies during 1995-1999 that found soy protein decreased blood cholesterol about an average 3-6% and provided the justification for a health claim. The latest research on soy protein and blood cholesterol continues to confirm the FDA’s decision to approve the health claim for soy and heart disease. For example, a recent review of the original studies used to inform FDA’s decision and of studies conducted since, led by well-known cardiologist Cesare Sirtori, confirmed that the cholesterol-lowering effect held up even when baseline levels of cholesterol were taken into account. Another recent meta-analysis found that soy protein significantly decreases total cholesterol, LDL cholesterol, and triglycerides, and increases HDL cholesterol. In a recent clinical trial, women with metabolic syndrome who ate soyfoods were able to decrease their LDL cholesterol levels by 5-10%. (8 -16) Learn more about soy and cholesterol.
SOY PROCESSING
10. How are soybeans processed? Does processing affect the health benefits or safety of soy?
Answer: All soybeans used to make soyfoods undergo some type of processing and a number of different processes are used, both traditional and modern. Traditional methods include germination, cooking, roasting, and fermenting. More modern processing methods remove undesirable constituents through fractionation or extraction. Traditional and modern processing can increase the digestibility of soy proteins, remove indigestible sugars, inactivate enzymes that affect flavor, and prevent undesirable changes that may occur during storage. In addition, numerous human studies have demonstrated that modern processing of soy produces foods that provide the same high-quality protein as traditional soyfoods. Overall, processing of soy produces safe and healthy soyfoods. (17)
11. What are trypsin inhibitors and are there any risks associated with consuming either trypsin inhibitors? What is lysinoalanine, and are there any risks associated with consuming lysinoalanine?
Answer: Trypsin inhibitors are small proteins that are also present in many other plant products including raw legumes, cereals, potatoes, and tomatoes. Some groups have raised questions about the safety of consuming raw soybeans because they contain trypsin inhibitors, which may reduce the efficiency of protein digestion. However, trypsin inhibitors are mostly destroyed when soybeans are heat processed to make soyfoods. Therefore, because humans do not consume uncooked soybeans, there are no risks associated with consuming trypsin inhibitors. In addition, small amounts of trypsin inhibitors that remain in a food may have beneficial health effects in reducing tumor growth and preventing the spread of some cancers.
Lysinoalanine is an amino acid that is found in proteins of cooked foods. Some have questioned the safety of the lysinoalanine in soy, but proper processing of soybeans minimizes any formation of lysinoalanine. (17 – 19) Lysinoalanine may be produced during modern processing; however, no evidence of adverse effects such as kidney lesions have ever been associated with human consuming lysinoalanine or processed soybeans.
ISOFLAVONES
12. What are isoflavones?
Answer: Isoflavones are bioactive compounds that are often described as phytoestrogens, plant estrogens because they are structurally similar to the female sex hormone estrogen. Soybeans are uniquely rich in isoflavones, primarily genistein and daidzein. Even though isoflavones have a similar structure to human estrogens, they act very differently in the human body, and therefore, should not be considered similar to human estrogens. Isoflavones are much weaker than naturally circulating human estrogens, as they have approximately 1/1000th the biological activity of synthetic estrogens. They do not have estrogen-like effects in humans and may actually function as anti-estrogens, inhibiting the effects of estrogen. (20 – 29)
13. Are there any health benefits or risks associated with consuming foods that contain isoflavones?
Answer: Yes, soyfoods provide a variety of health benefits and the isoflavones found in soyfoods are thought to contribute to many of the protective effects shown in animal and in-vitro studies. For example, isoflavones may improve the health of arteries, prevent certain cancers, and reduce bone loss. The isoflavones taken from soyfoods are different from highly refined genestien or other independent isoflavones. Research has shown that individuals consuming diets rich in phytoestrogens from soy do not have any signs of infertility. (20 – 29) Learn more about soy safety.
14. Is there a recommended daily isoflavone intake?
Answer: No, at this time, there is not enough research available for the FDA to make specific isoflavone intake recommendations. The FDA, when approving a health claim, "25 grams of soy protein may help reduce the risk of heart disease", the agency did not find any potential adverse effects. Twenty-five grams of soy protein contains approximately 50 milligrams of isoflavones. The isoflavone content of soyfoods is available on the SANA soyfood fact sheets or you can visit the isoflavone database on the USDA web site. (8)
15. Is taking an isoflavone supplement the same as eating soyfoods?
Answer: No, taking soy isoflavone supplements may not be the same as eating soyfoods as research has shown that the body breaks down the isolated isoflavones in a supplement differently than when they appear in a food. The biological effects of isolated isoflavones may be different from the effects of isoflavones found naturally in food. (30, 31)
SOY AND CANCER
16. Is there any relationship between consumption of soyfoods and breast cancer risk?
Answer: Yes, women who eat more soyfoods have a lower risk of developing breast cancer, compared to those who eat less soyfoods. Eating soyfoods at any age, especially when soy is consumed during childhood and adolescence, as part of a healthy diet appears to protect against developing breast cancer. In a study that showed a protective effect of soy against breast cancer, the median intake of soy among those who consumed the most soy was 2 times per week for adults, 3 times per week for adolescents, and 2½ times per week for children. Eating soyfoods early in life may be one of the factors that explains why Asian women have lower breast cancer rates, as low as one-fifth that of Western women. In addition, recent research suggests that there is not an increased risk of breast cancer for post-menopausal women, women at-risk of developing breast cancer and breast cancer survivors who consume soyfoods. (32 – 38) Learn more about soy safety.
17. Does eating soy provide more estrogen than the body can handle?
Answer: No, soyfoods do not contain estrogens. Soyfoods contain complex mixtures of proteins, fats, carbohydrates, and bio-active compounds including soy isoflavones. Although isoflavones naturally found in soy are plant “phytoestrogens” that look similar in chemical structure to estrogens, they act differently in the human body and should not be confused with the human hormone estrogen. Isoflavones are bioactive compounds that may improve the health of arteries, prevent certain cancers, and reduce bone loss. (38-42)
Numerous human studies have found that men and women consuming 40-70 mg/day of soy isoflavones from soyfoods or soy supplements had no significant changes in testosterone levels or estrogen levels compared to control groups. (43 – 49)
Some animal studies that are looking for effects inject or feed a very high dose of a concentrated source of a single isoflavone, such as genistein, which is very different from the way isoflavones are consumed in food. Problems seen in some animals but not humans are believed to be due to differences in the way soy isoflavones are metabolized by humans and animals. (50)
18. Is there any relationship between consuming soyfoods and the risk of developing colon, lung, ovarian, liver, stomach, esophageal, prostate, or pancreatic cancer or leukemia?
Answer: No, there is no human evidence that consumption of soyfoods causes colon, lung, ovarian, liver, stomach, esophageal, prostate, or pancreatic cancers. For colon cancer, overall the research points to a reduced risk in humans, although the reduced risk may be limited to the consumption of unfermented soyfoods. A study on lung cancer found that increased soy consumption by nonsmokers lowered risk for this cancer. Consuming more soy may lower a woman’s risk for ovarian cancer. Also, evidence is growing that soy may in fact reduce risk of prostate cancer. Dr. Wang and others explored the potential mechanism for the impact of soy on pancreatic cancer and found that genistein inhibited activity of some cell nuclear factors; and thus inhibits cell growth and induces apoptotic processes in pancreatic cancer cells.
There is also no human evidence linking leukemia to soy consumption. The American Cancer Society confirms that there are no known nutritional risk factors for leukemias or lymphomas. Toxicity studies in animals where extremely high doses of pure genistein were administered until cells become cancerous do not signal a risk to human health. (51 – 56)
SOY AND THYROID FUNCTION
19. Is there any relationship between soyfood consumption and thyroid function or the development of goiter?
Answer: A recent review of human health research found that soy users who had ample iodine in their diet were not at increased risk for thyroid problems or goiter. In fact, the findings of a recent human study suggest that consumption of both traditional and modern soyfoods is associated with a reduced risk of thyroid cancer. There is a chance that soy, other high-fiber foods, and certain dietary supplements may interfere with medication for hypothyroidism. Individuals treated for hypothyroidism can consume soyfoods safely, but should discuss their diets with their physician. (57 – 58)
Reports of goiter and hypothyroidism in human infants fed soy-flour based formulas in the 1960s predate the supplementation of soy protein based formulas with iodine. Today, the American Academy of Pediatrics recognizes iodine fortified soy-based infant formula as a safe and effective alternative for infants allergic to cow’s milk to provide appropriate nutrition for normal growth and development. (59) Learn more about soy and the thyroid gland.
CHILDREN AND SOY
20. Is it safe for pregnant/lactating women to consume soyfoods?
Answer: Yes, soyfoods are safe to consume throughout the life cycle. Mothers who consume traditional soyfoods as a normal part of their diet throughout their lifespan, including pregnancy and lactation, do not show evidence of growth or endocrinological problems. According to a scientific panel convened in March 2006 by the National Institute of Environmental Health Sciences (NIEHS), even pregnant women who eat soy regularly consume such low amounts of genistein, the most heavily concentrated isoflavone in soy, that the likelihood of reproductive or developmental effects are of “negligible concern.” If any problem has ever been observed, it has only been in animal studies,not in humans, and have used very large amounts of genistein. Animals break down isoflavones such as genistein quite differently than do humans, so animal studies should not be used to determine effect in humans. (59 – 65) Learn more about soy and pregnancy.
21. Is it safe for infants to consume soy-based formulas?
Answer: Yes, soy-based infant formulas have similar benefits to cow’s milk-based formulas, and that there are no risks associated with consuming soy-based formulas, according to an American Academy of Pediatrics position on soy-based formula. There is no evidence of negative effects on babies fed soy-based foods and formulas or on adults who were fed soy-based foods and formulas as infants. Authors of a retrospective trial to evaluate soy-based infant formula’s potential hormonal influences on development concluded that long-term feeding with soy-based infant formula in early life does not produce estrogen-like hormonal effects. Soy formula provides an alternative to dairy-based formulas for infants with allergies, galactosemia, lactose intolerances or vegans. (59 – 65)
22. Is it appropriate for children to consume soymilk?
Answer: Yes. Soymilks fortified with calcium and vitamin D should be part of a healthy diet for children over 12 months of age who do not consume cow’s milk. The USDA’s 2005 Dietary Guidelines for Americans and Food Guide Pyramid for Young Children both identify fortified soymilk as a healthy food choice and non-dairy alternative. Soymilks, however, are not a substitute for infant formula. (66) Learn more about soy and children.
23. What are protease inhibitors and do they have an adverse effect on growth?
Answer: Protease inhibitors are a class of proteins found in numerous plant foods, including rice, maize, and beans. Soybeans are particularly rich in protease inhibitors. There is no good evidence that soybean-derived protease inhibitors have an adverse effect on growth and human health. In fact, a growing body of data suggests that these compounds may in fact enhance human health through their cancer preventative effects. (67 – 69)
SOY ALLERGIES
24. Is soy protein an allergen?
Answer: Soy protein is one of the eight major food allergens, along with proteins from milk, eggs, peanuts, tree nuts, fish, shellfish, and wheat. However, only an estimated 0.1% of Americans are allergic to soy. Although an individual could be allergic to any food, such as fruits, vegetables, and meats, the previously listed eight foods account for 90 percent of all food-allergic reactions. Individuals who experience allergies are advised by their physicians or nutritionists to avoid the foods that cause these reactions. Consumers allergic to soy protein can refer to the ingredient list on the product to identify what foods contain soy protein. The Food Allergy and Anaphylaxis Network is an excellent resource for people with food allergies. Contact www.foodallergy.org or 1-800-929-4040. (70) Learn more about soy and allergies.
COGNITIVE FUNCTION
25. Do soyfoods impact cognitive function?
Answer: Recent data from clinical trails on humans finds that soy may actually improve brain function, and does not decrease it. Recent studies are finding that soy isoflavones may enhance short term memory and executive function in women. In a study of 30 cognitively-healthy adults over the age of 60, those who reported eating soyfoods as part of their normal diet performed better on cognitive tests than those who did not. (70)
One previous study raised questions about soy’s impact on cognitive function in older men, but the interpretation of the data, collected for another purpose, were flawed. A University of Hawaii researcher, Dr. Lon White, reviewing previous data collected on food intake from Japanese-American men observed a possible association between high tofu intake and loss of cognitive function. The men in the population study who consumed large amounts of tofu differed significantly from the other men in the study: they were older by over two years (may account for the differences in the brain size), had suffered more strokes (a condition that directly compromises cognitive function), and had come from poorer families (possibly with compromised nutrition in utero and infancy that would limit brain development). Age, education, and history of a stroke explained 28 percent of the differences in test scores of thinking ability or cognitive function. (71 – 75) Learn more about consuming soy at every stage of life.
PHYTIC ACID
26. Does phytic acid, which is found in soy, cause problems with mineral absorption?
Answer: No, when people’s diets are adequate in zinc, iron, and calcium, phytates from soy or other vegetables and grains do not present a problem with mineral bioavailability. Phytic acid, a component of all plants, has benefits and detractions. Phytic acid affects mineral bioavailability, particularly zinc, iron, calcium and copper. It has the capability of forming complexes with these elements, making them less available. Possible beneficial effects of phytic acid include its antioxidant property, which reduces free radical formation. Phytic acid has been shown to have positive effects on lowering serum cholesterol and triglycerides, suppressing iron-mediated oxidation and preventing some cancers. (76 – 81)
BLOOD-THINNING MEDICATIONS AND SOY
27. Can people taking blood-thinning medication consume soyfoods?
Answer: Yes, it is safe to consume soyfoods is you are taking a blood-thinning medication. The dietary goal for individuals taking blood-thinning medication, such as warfarin, is to consume a consistent amount of vitamin K. The vitamin K content of soy products varies widely, so if you already consume soyfoods as part of your diet, you will want to maintain that level of intake. If you are interested in adding soyfoods to your diet, please discuss this dietary change with your physician, so that your blood work can be monitored and medication adjusted if necessary. In addition, you should discuss any dietary changes and vitamin/mineral supplement intake–not just related to soyfoods–with your physician or dietitian. (82)
For Additional Frequently Asked Questions Please Visit The StratSoy Website.
Frequently Asked Question Complete References.
Updated May 2008.
