Winter 2000 Issue — Soy isoflavones: A functional ingredient

Liesbeth Neven M.Sc and Marian Verbruggen Ph.D

Soylife Nederland BV, P.O. Box 1, 4283 ZG Giessen, The Netherlands

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1. Introduction

Soy products are gaining interest in the health food industry, because of the increasing collection of scientific results proving their beneficial effects. Soy is known to contain high quality proteins and lipids, and many blo-active components like tocopherols, oligosaccharides, saponins and phytosterols. Research focuses on isoflavones, of which soy is a rich source. Exposure to these phyto-estrogens is increasingly associated with a lower risk of the so-called "Western" diseases: e.g. heart disease, osteoporosis and several cancers. Consequently, the industry takes up this opportunity to develop unique products that offer the consumers an alternative to consuming traditional soy foods like tofu, miso or soy milk. Isoflavone concentrates and extracts are increasingly used in dietary supplements and functional foods.

Figure 1: Chemical Structure of Soy Isoflavones

2. Properties of Isoflavones

Phyto-estrogens are dietary nonsteroidal plant compounds of diverse structure that produce estrogenic responses. They vary greatly in both their potency and physiological effects. There are three main classes of phyto-estrogens: isoflavones, coumestans and lignans, which are present in either plants or their seeds. Isoflavones in four chemical forms: the aglycons daidzein, genistein and glycitein; the glucosides daidzin, genistin and glycitin; the acetyiglucosides and the malonylglucosides(1). Isoflavones are structurally similar to the mammalian estrogen, estradiol. The principal compounds within these classes of phyto­estrogens have been shown to have weak estrogenic activity, ranging from 0.002 to 0.001 the activity of estradiol.(2) Their effect can both be agonistic and antagonistic to 17-ß estradiol when they act simultaneously at target tissues. Antagonistic compounds normally compete for 17-ß estradiol receptors but fail to exert a similar estrogenic effect.(3)

3. Health Effects of Isoflavones

The above raises the interest in isoflavones as protective agent for hormone-related diseases, as menopause, osteoporosis and coronary heart disease and breast cancer.

4. Menopause

The hot flush is the most common and disruptive symptom of the menopause. Estrogen replacement therapy eliminates 60% of flushes within three months. Hormone replacement generally alleviates the condition, as well as the vaginitis occurring at the menopause due to atrophy. However, due to increasingly suggested and reported negative side effect of hormone replacement therapies, women today request dietary and natural' options for symptom management. The rarity of the problem in soy consuming countries has prompted some investigations to determine whether phyto-estrogens have a similar effect. Human studies have shown that soy isoflavone supplementation resulted in significant reduction in the frequency and intensity of hot flushes and increases serum levels of SHBG, which in turn may alleviate symptoms such as hot flushes and vaginal dryness.(4-6)

Figure 2: Consuming two to four bakery products from this ReVitaal line delivers the daily dosage of isoflavones.

 5. Osteoporosis

Osteoporosis in women is particularly associated with menopause, since the loss of estrogen accelerates bone loss. The hormonal effect of phyto-estrogens, coupled with the comparative rarity of the disease in populations consuming soy, has also prompted investigation of their effects on osteoporosis. Dietary effects have been investigated for achieving peak bone mass and preventing bone loss in later life.(7) It has even been showed that isoflavones do not only prevent the loss of bone, but even allow significant increases in both mineral content and bone mineral density in the lumbar spine region. Similar trends were notes for other skeletal areas.(8) An important role in this effect is ascribed to daidzein. More human studies are currently conducted.
Coronary Heart Disease (CHD) The importance of lowering serum cholesterol in reducing the risk of CHD, and total mortality, is now well established.(9) As CHD is a multi-factorial disease, many dietary factors are involved in affecting risk. LDL­lipoproteins are normally taken up by the liver, thus maintaining levels of serum cholesterol, but if they are oxidatively damaged they are taken up by macrophages to form foam cells in the lining of arteries, initiating the first stages of atherosclerosis.(10) In soy, the positive role of soy proteins is strongly recognised. The Food and Drug Administration in the US has approved a health claim for cholesterol lowering effect when consuming 25g of soy protein per day. The isoflavones may prevent oxidative damage through their antioxidant activities, and are believed to support an improved HDL/LDL ratio. Furthermore because of its effects on tyrosine kinases, genistein may have a role in suppression of the cellular processes which lead to atherosclerosis.

6. Cancer/Immune Function

High soy consumption leading to high exposures of soy isoflavones has been associated with a reduced risk of cancers at many sites. Several studies on experimental animals and cell cultures have demonstrated cancer chemo-preventive effects of soy isoflavones. In addition to weak estrogenic activities, isoflavones possess a variety of characteristics such as antioxidant, anti-proliferative and differentiation-inducing abilities. A recent study shows that isoflavones might also increase the metabolism of endogenous estrogens to the protective 2-hydroxylated estrogens in women, and this may play an important role in lowering 1 7ß-estradiol levels and the long-term risk for breast cancer.(11) Also the role of the immune function has become increasingly important in our understanding of the mechanisms underlying the body's ability to prevent cancer. At high doses, especially daidzein was shown to enhance several immuno-regulatory functions (12)

7. Bio-activity

Diet derived health protectants, like the isoflavones, need sufficient systemic bio­availability to exert the beneficial effects. Determinants of isoflavone bio-activity are structural differences between the isoflavones, gut micro-floral metabolism and mammalian phase-II metabolism. Gut micro-floral influences seems a major factor in inter-individual variation in isoflavones blo­availability. Individuals who excrete larger amounts of faecal isoflavones have much higher urinary and plasma isoflavone levels than individuals who excrete small amounts of isoflavones in faeces. Moreover, these high excreters experience more prolonged plasma diadzein and genistein.(13) Research has shown that glycitein and daidzein are more blo­available than genistein.(14) Urinary recovery of glycitein and daidzein was about 47% and 52% respectively after a single soy dose, whereas the recovery of genistein was 37%. Genistein's lower bio-availability may be due to its more rapid degradation in the gut compared with daidzein and glycitein.

8. Market and Product Application

The physiological effects of phyto-estrogens have also created a marketing opportunity that has been utilised by the industry, particularly in soy producing countries such as the USA and Australia. In the whole soybean, the isoflavones are present in a concentration of 0.2-1.5mg/g. The traditional oriental daily isoflavone intake has been estimated at 25-100 mg/day. This amount would mean a daily traditional soy food consumption of at least 20-150g. In our modern society our dietary habits do not fit with this requirement. Isoflavone supplements and isoflavone-enriched food products could be a solution.

Many 'health' supplements are now marketed for example as natural hormone-replacement therapy, bone health product or immune-enhancing agent, available over the counter or in the supermarket. Also functional foods, designed and processed to provide health benefits for the consumer, are increasingly developed with natural isoflavone concentrates. (Fig 2).

An attractive ingredient for application in these products is SoyLife™'s natural soy Complex, which encompasses an enriched level of isoflavones, preserved in their natural complex of elements, as proteins, oligo­saccharides, and omega-3 and omega-6 fatty acids and other micronutrients. SoyLife™'s natural isoflavones content refers to the history of safe use, that soy enjoys since it has been consumed in Asia for over 4,000 years. Health benefit hypotheses and finding in studies on soy and isoflavones in general, also seem to be confirmed by studies done with SoyLife™. Research has shown a better bin-availability of SoyLife™ isoflavones that of soy milk isoflavones.(4)

Physical characteristics make SoyLife™ suitable for all kinds of product applications. Isoflavones are heat-stable, so they do not loose activity during baking processes. The ingredient is increasingly used by the dietary supplements industry, in capsules and tablets, as well as by the growing functional foods industry, in numerous applications such as bars, bread, crispbread, breakfast cereals, extruded products, meat-alternatives, dairy products and beverages.

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