Frequently asked questions about whole soy

What is soy?

All soy comes from soybeans, which are naturally grown beans similar in size to a pea. Soy is a nutrient-rich food delivering high-quality, complete protein, carbohydrates, fiber, healthy fats and a number of vitamins and minerals important to good health.

Is soy a good source of protein?

Soybeans have more protein than any other bean and are the only plant-based protein source that contains a high proportion of all nine essential amino acids, making it a source of high-quality, complete protein.

What is whole soy? Why choose whole soy?

It is important to look for foods made from whole soy, which means the soy is minimally processed and you are getting all of the naturally occurring nutrients contained in the soybean. Many soy products use only part of the soybean, essentially squeezing out some of the benefits of the bean such as some of the fiber, vitamins and minerals.

What are the health benefits of whole soy?

Soy in its whole form delivers not only isoflavones (plant-based compounds with antioxidant properties) but a number of essential nutrients important to good health. Whole soy is a rich source of fiber, protein, healthy fats and vitamins and minerals including folate, potassium, magnesium, zinc, iron and calcium.

What foods contain whole soy?

Popular foods that contain whole soy include whole soybeans and dry roasted soy nuts.

What is soy protein isolate?

Unlike whole soy, soy protein isolate, commonly found in “foods with soy,” is processed and does not contain all of the benefits of the bean such as some of the fiber, vitamins and minerals.

What are isoflavones?

Soy is rich in isoflavones – plant-based compounds called phytoestrogens that have estrogen-like activity but are very different from human estrogen. Isoflavones are thought to positively affect the health of men and women.

How do isoflavones affect health?

Soy isoflavones are one of the most studied compounds found in whole soy. Some research has suggested they may help build strong bones, maintain a healthy heart, and maintain hormone balance during menopause.

How does soy affect the heart?

Soy is good for the heart because it is high in soy8th protein and fiber, contains heart-healthy fats and micronutrients, and is low in saturated fat and cholesterol free.

In April 2009, a Journal of Nutrition report summarized findings from the 8th International Soy Symposium held the previous year in Tokyo. The most comprehensive systematic review presented at the symposium, covering the years 1978 through the present, found that about two-thirds of the studies judged to be of high or moderate quality showed a statistically significant reduction in either total cholesterol or LDL (bad) cholesterol. In addition, the meta-analysis presented showed a net reduction in LDL (bad) cholesterol of approximately 5 percent, which is in line with other data.1

Messina, M., Watanabe, S., Setchell, K. D. R.. Report on the 8th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment. J. Nutr. Apr;139(4):796S-802S

What is it about soy that lowers cholesterol levels?

The cholesterol-lowering effect of soy is directly related to soy protein and not only to its low saturated fat content (McVeigh, 2006; Omoni, 2005). After a recent review of the research on soy’s cholesterol-lowering effect, Dr. Sirtori reported that soy protein was effective not only when it replaced products high in saturated fat and cholesterol, but also when it was a partial substitution or addition to a regular diet (Sirtori, 2007). Dr. Francene Steinberg notes in a recent editorial published in the American Journal of Clinical Nutrition that studies consistently find soy protein lowers cholesterol (Steinburg, 2007). A 2007 meta-analysis suggests there is building evidence that soy’s lipid-lowering action may be enhanced when isoflavones are provided with soy protein, and it also reinforces an independent effect of soy protein on blood cholesterol (Taku, 2007).

McVeigh, BL, Dillingham BL, Lampe JW, Duncan AM. Effect of soy protein varying in isoflavone content on serum lipids in healthy young men. Am J Clin Nutr. 2006;83:244-51

Omoni AO, et al. Soybean foods and their benefits: Potential mechanisms of action. Nutr Rev. 2005; 63:272-83. 

Sirtori CR, Eberini I, Arnoldi A. Hypocholesterolaemic effects of soya proteins: results of recent studies are predictable from the Anderson meta-analysis data. Br J Nutr. 2007 May;97(5):816-22.

Steinberg, F. Soybeans or soy milk: Does it make a difference for cardiovascular protection? Does it matter?. Am J Clin Nutr. 2007:85: 927

Taku K, Umegaki K, Sato Y, Taki Y, Endoh K, Watanabe S. Soy isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials. Am J Clin Nutr. 2007 Apr;85(4):1148-56.

Why is the FDA reevaluating the evidence on soy and heart health?

In 1995, a meta-analysis published in the New England Journal of Medicine reported that soy protein lowered LDL cholesterol by 12.9% (Anderson, 1995).

In 1999, the FDA concluded through an authorized claim that “25 grams of soy protein per day, as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease.”

Research following the 1995 study found that the effect of soy protein on cholesterol was much lower than previously reported in the 1995 study, although there still is a lowering effect with more recent estimates ranging from about 3-5% reduction in LDL-cholesterol (Sacks, 2006; Zhan, 2005). Even at these lesser levels of cholesterol reduction, soy protein would reduce the risk of heart disease as the FDA claim originally asserted. Even a 3-5 percent reduction in cholesterol can potentially reduce the risk of heart disease by up to 10 percent.

In 2007, the FDA decided to reevaluate and update the claim since the body of evidence continued to grow during the 10 years since the original claim.

Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med. 1995;33:276-82.

Sacks, FM., et al. Soy protein, isoflavones, and cardiovascular health:an American Heart Association Science Advisory for professionals from the Nutrition Committee. Circulation. 2006, 113:1034-44.

Zhan, S. Meta-analysis of the effects of soy protein containing isoflavones on the lipid profile. Am J Clin Nutr. 2005;81:397-408.

How does soy affect bone health?

Soybeans and calcium-fortified soy foods are good choices for bone health because they contain soy isoflavones as well as bone-building calcium and vitamin K, which are essential to bone mineralization.

There has been great interest in the effects of soy on bone mineral density in menopausal women because of the estrogen-like effects of isoflavones.

In April 2009, a Journal of Nutrition report summarized findings from the 8th International Soy Symposium held the previous year in Tokyo. During the symposium, promising results were presented on the benefit of soy and bone health. Among the findings of the three main studies discussed, results showed that one of the isoflavones in soy significantly increased bone mineral density in a clinical three-year study in postmenopausal women; two large prospective cohort studies, one in Shanghai and one in Singapore, found one-third reduction in hip fracture in women who consumed soy isoflavones (Messina, 2009).

Messina, M., Watanabe, S., Setchell, K. D. R.. Report on the 8th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment. J. Nutr. Apr;139(4):796S-802S

Does soy increase the risk of breast cancer?

A protective effect against breast cancer may occur when soy consumption is high before puberty.

There is little evidence that increasing soy or soy isoflavone consumption dramatically during the adult years reduces breast cancer risk.

Although some animal data suggests that some soy isoflavones, but not whole soy foods, might stimulate breast cancer growth in certain women, human clinical trials support the safety of soy and soy isoflavone consumption. There is no evidence to suggest that consuming traditional soyfoods is harmful.

Furthermore, researchers at Vanderbilt University found that soy has either no impact or a favorable impact on breast cancer outcomes.

Postmenopausal women are advised to consult with their physician before considering isoflavone supplements. This advice is consistent with the evidence presented at a recent symposium in 2008

Messina, M., Watanabe, S., Setchell, K. D. R.. Report on the 8th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment. J. Nutr. Apr;139(4):796S-802S

Is soy safe to consume for breast cancer survivors?

The American Cancer Society suggests that up to three servings of soyfoods a day is safe to consume for a breast cancer survivor.

Can soy intake reduce the risk of breast cancer?

A recent study published in the journal Cancer Epidemiology, Biomarkers, and Prevention looked at lifetime soy intake and breast cancer risk among American women of Asian descent. The researchers found that soy intake during childhood was associated with decreased breast cancer risk, suggesting early exposure may have the most positive preventative effect (Korde, 2009).

Korde et al. Childhoood soy intake and breast cancer risk in asian american women.Cancer Epidemiol Biomarkers Prev.2009;Epub ahead of print.

Does soy help alleviate menopausal symptoms, like hot flashes?

In 1992, researchers began to think, based on emerging evidence, that soyfoods might account for the fact that many Japanese women did not experience hot flashes. Since that time, more than 50 trials have examined this issue. A recent summary analysis of research on this topic was presented in Milan and concluded that the overall reduction in hot flash frequency and severity from soy is about 50 percent. Research published in the Experimental Gerontology Journal in 1994 found that the percentage of women experiencing hot flash symptoms was much lower among Japanese and Chinese women than among those in North America (Lock, 1994). This finding prompted researchers to examine cultural differences, which led to much investigation of soy’s potential role in alleviating hot flash symptoms.

A systematic review and meta-analysis of all studies that used soy isoflavones as a treatment for menopausal symptoms was completed in 2006 and published in the Maturitas Journal (Howes, 2006). The researchers found that percentage in reduction of hot flashes was significantly related to number of hot flashes a women experienced, with those experiencing more hot flashes reporting more relief from soy isoflavones, and was dependent upon the dose of soy isoflavones provided.

Lock M. Menopause in cultural context. Exp Gerontaol.1994;29(3-4):307-317.

Howes LG, et al. Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis. Maturitas. 2006;55:203-11.

Can soy intake decrease sperm count, delay puberty or decrease size of sexual organs?

Researchers presenting in Tokyo reported on two studies that assessed the impact of soy intake on both sperm and semen parameters. In one crossover study conducted on 32 healthy young men consuming diets in random order supplemented with milk protein isolate, low-isoflavone isolated soy protein or high-isoflavone soy protein, no significant effect of diet on semen parameters was observed, including semen volume, sperm concentration, sperm count, total motile sperm count, sperm motility or sperm morphology. In the second study, 20 volunteers were randomized to receive different levels of isoflavones for 3 months. When compared to baseline, there were no statistically significant differences in ejaculate volume, sperm concentration, count and motility of spermatozoa in men given isoflavones (Messina, 2009).

In addition, three intervention studies with men consuming 40-70 mg/day of soy isoflavones from soy foods or soy supplements failed to show effects on plasma hormones or semen quality.

There are no human data that show that consuming soy causes abnormal testosterone or estrogen levels. Other human trials found that men consuming 40-70 mg/day of soy isoflavones from soy foods or soy supplements have shown no significant changes in testosterone levels compared to control groups or baseline levels (Kuzner, 2002; Rubin, 2005; Dillingham, 2005)

Messina, M., Watanabe, S., Setchell, K. D. R.. Report on the 8th International Symposium on the Role of Soy in Health Promotion and Chronic Disease Prevention and Treatment. J. Nutr. Apr;139(4):796S-802S

Kurzner MS. Hormonal effects of soy in premenopausal women and men. J. Nutr. 2002;132(3):570S-573S.

Rubin S, Kalman D, Martinez M, Krieger DR, A Randomized Double-Blind Clinical Pilot Trial Evaluating the Effect of Protein Source when Combined with Resistance Training on Body Composition and Sex Hormones in Adult Males, FASEB, 2005.

Dillingham BL, McVeigh BL, Lampe JW, Duncan AM. Soy protein isolates of varying isoflavone content exert minor effects on serum reproductive hormones in healthy young men. Journal of Nutrition 2005; 135:584-591

Does soy impact thyroid function or the absorption of synthroid (medication for hypothyroidism)?

A comprehensive review of the literature published in 2006 concluded that soy does not adversely affect thyroid function. The review further recommended that thyroid function be reassessed if there is a substantial increase or decrease in soy intake, but normal day-to-day variations are unlikely to affect normal thyroid function.

Messina M, Redmond G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid. 2006 Mar;16(3):249-58.

How is soy an “environmentally friendly” choice?

One way that soy is environmentally friendly is that soy is an energy efficient crop and protein source. We get more energy (that is calories) from soy for every calorie of inputs (e.g. fertilizer, production etc.) that we put into a soy crop than for any animal source of protein. For example, using one calorie to produce chicken generates 18.1 calories of energy, beef generates 6.4 calories, but soy generates 415 calories of energy for every one calorie invested (Eshel, 2005).

Eshel G, Martin, P. “Diet, Energy, and Global Warming” Dept. of Geophysical Sciences, Univ. of Chicago, 2005.

How much carbon dioxide does soybean production create?

Production of soybeans results in negligible carbon dioxide emissions because soybeans absorb carbon dioxide and, depending on agricultural technique, can even serve as a carbon sink in economic analysis. A certain amount of fossil fuels are used in soybean processing, but this is estimated to be 6 to 20 times less than that used in processing meat (Fiala, 2006).

Fiala N. “Is Meat Sustainable? An Estimation of the Environmental Impact of Meat Consumption” Department of Economics, Univ. of California, 2006.

How does soybean production impact land use and erosion?

Soybean production generally requires anywhere from six to 17 times less land than meat production and at least five times less than intensive dairy operations (Reijnders and Soret, 2003). As for topsoil erosion, soybean crop production only erodes 400 tons per kilometer squared per pound of output compared to 8800 tons per km squared per pound of beef (Fiala, 2006).

Reijnders L, Soret S. “Quantification of the environmental impact of different dietary protein choices” American Society for Clinical Nutrition, 2003.

Fiala N. “Is Meat Sustainable? An Estimation of the Environmental Impact of Meat Consumption” Department of Economics, Univ. of California, 2006.

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