Food Product Design: Nutrition Notes - November 2000 - Building Better Bones

November 2000

For years, soy has been a significant protein source for many Asian countries. These countries have also seen a low incidence of several chronic diseases that plague the Western countries. Part of the reason may be soy isoflavones.

Isoflavones are a type of phytoestrogen, plant-based compounds with weak estrogenic activity. There are many types of phytoestrogens, but those known as isoflavones are found in chickpeas and legumes, with soy having the most concentrated amount. The actual content varies depending on the type of soybean and other factors. On average, soybeans contain approximately 190 mg isoflavones per 100 grams raw beans. Most soy-protein ingredients contain isoflavone levels of 10 to 300 mg per 100 grams. Optimal or recommended dietary isoflavone intake is not known at this time and may vary depending on the effect sought.

The main isoflavones found in soy are genistein and diadzein, with lesser amounts of glycitein and glycitin. Genestein and diadzein are typically present in approximately a 1:1 ratio in soy, and although most research has focused on the effects of genistein, both appear to be biologically active. In addition, these two isoflavones may be present in different forms both before ingestion and when transformed by fermentation in the gut; this may also play a role in their physiological effect. So while these compounds still require study, says Jocelyn Mathern, R.D., Schouten USA, Minneapolis, MN, recent research suggests that they may play a role in lowering cholesterol levels, reducing the risk of osteoporosis, relieving some symptoms of menopause, and preventing heart disease and certain cancers.

"When manufacturers are selecting soy ingredients, they should look for those ingredients that have been processed the least. This will assure that the soy isoflavones and other components are in their natural environment where they probably have the most benefit, as opposed to isolated compounds," suggests Mathern.

Healthy heart

"A daily consumption of 25 grams of soy protein has been shown to lower total cholesterol levels, LDL cholesterol and triglycerides, which can help prevent heart disease," says Mathern. "It is suggested that soy isoflavones along with soy protein is attributed to the lowering of cholesterol levels, though the precise mechanism of action remains unclear." Some hypotheses include changes in hepatic metabolism of cholesterol and lipoproteins; a reduced rate of oxidation of LDL cholesterol due to the antioxidant activity of the isoflavones; and influences on the endocrine system.

Mathern adds that since isoflavones are phytoestrogens, they act like weak estrogens in the body when ingested and can decrease heart disease risk commonly seen in menopausal women. In addition, "men with high cholesterol levels can benefit from soy isoflavones since these phytoestrogens help to reduce the risk of heart disease by lowering the LDL cholesterol level," she says.

In 1996, Anthony, Clarkson and colleagues published three studies conducted on monkeys ("Soybean isoflavones improve cardiovascular risk factors without affecting the reproductive system of peripubertal rhesus monkeys") in the Journal of Nutrition. These studies suggest that isoflavone-rich soy protein may have accounted for 60% to 70% of the favorable lipid concentrations while soy protein from which the soy isoflavones were extracted, had a minimal effect in the lipid profile.

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Cancer care

Isoflavones may fight against cancer. "Evidence suggests that people who consume large amounts of soy, such as the Asian population, have lower rates of breast, prostate and colon cancers," says Mathern. Mark Messina, Ph.D., Nutrition Matters Inc., Port Townsend, WA, recommends consuming approximately 30 to 60 mg of isoflavones for reducing cancer risk.

Mathern explains that soy components, such as the isoflavone genistein, inhibit tumor growth. Genistein stimulates TGF-beta1 synthesis and therefore limits uncontrolled cell growth. It also inhibits certain protein tyrosine kinases that promote cancer cell growth. Another hypothesis is that genistein stabilizes critical enzymes that phosphorylate tyrosine residues on key proteins involved in signal transduction in both normal and tumor cells. Research has found that soy’s anti-cancer effects are not just from isoflavones, but also from tryspin inhibitors and other biologically active components found in soy.

There are some concerns that soy may encourage breast cancer cell growth — since isoflavones may also act like the hormone estrogen, it may actually promote tumor growth. "Until long-term studies are done, it is suggested that women with breast cancer or those with a high risk for the disease should consult with their physician, consume moderate amounts of soy and stay away from large amounts of soy supplements," cautions Mathern.

However, according to Trevor Meredith, R&D, Solbar Plant Extracts, Asdod, Israel, "While soy isoflavones mimic the effects of natural female hormones, they are recognized to be weak estrogens, easily broken down and not stored in tissue."

And of course, males should not shy away from soy, explains Mathern. "Men can benefit from soy foods since they help inhibit the growth of prostate cells. Men may worry that soy will feminize them, but it is important to remember that soy isoflavones are 1000 times weaker than estrogens in the body, so feminization at the recommended levels is unlikely."

Additional benefits from soy

Asian women — who are less prone to hot flashes during menopause than American women — include approximately 25 to 40 mg of soy isoflavones in their daily diet. Researchers attribute this to the isoflavones’ weak estrogenic effect.

"Soy may possibly help prevent osteoporosis by decreasing bone loss," states Mathern. One theory is that the isoflavones bind to the ER-beta cells as well as inhibit the activity of bone cell tryosine kinases. A 1998 study by Potter et al. at the University of Illinois, Urbana-Champaign — conducted on 66 postmenopausal women over a six-month period, with three different interventions — found that the high isoflavone diet (40 grams of soy protein with 90 mg of soy isoflavones daily) resulted in significant increases in the lumbar-spine bone mineral content and bone density compared to the control group.

Soy’s future

Soy consumption has increased in the United States due to its scientifically proven health benefits. As the research continues, more functional food products containing soy will emerge.

"Most of the effects of soy isoflavones are still speculative, but research in the areas of heart disease, prostate cancer and osteoporosis looks very promising," says Messina.

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