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Interest in Isoflavones Continues To Increase

By Mark Messina, Ph.D.

Anyone even remotely familiar with soyfoods, or who casually reads this newsletter knows about the very provocative research suggesting soy may offer a number of health benefits related to heart disease, osteoporosis, menopause symptom relief and possibly cancer. While soybeans have much to offer from a nutritional perspective, it is because they contain isoflavones that so much attention is focused on this legume. And while the pace of isoflavone research has been steadily growing during the past three to four years, it seems that within just the past six months, there has been a quantum leap in interest in isoflavones among both the research community (see back page) and consumers, as demand for isoflavone pills and soyfoods increases. It has become somewhat of a necessity for many health professionals to know something about soy/isoflavones.

Some of the "new" interest in isoflavones undoubtedly stems from interest in the development of SERMs, selective estrogen receptor modulators. These are compounds that are designed to retain the benefits of estrogen without its unwanted effects. That is, ideally SERMs exert estrogenic actions in tissues where that effect is thought to be beneficial, such as the bones and heart, but would have no effect or even an antiestrogenic effect in tissues such as the uterus and breast where estrogenic effects are undesirable. There has been much news recently about one such SERM, raloxifene, which has been shown to improve bone health without exerting an estrogenic effect on the endometrium, and which may even exert an antiestrogenic effect on breast tissue. However, raloxifene does not relieve hot flashes nor does it seem to offer protection against heart disease to the same extent as estrogen (1).

As we seemingly reach a new high point on isoflavone research, it is appropriate to get perspectives from two pioneering researchers in this field. For the past ten years Dr. Stephen Barnes has been doing research on the mechanism of isoflavone action at the cellular level, but also has studied isoflavone pharmacokinetics, and conducts animal and human studies in the area of cancer and bone health. Dr. Kenneth Setchell has been doing isoflavone work for two decades. It can be said that this field started with his and his colleagues' initial identification of isoflavones in the urine of laboratory animals. He has continued to conduct ground-breaking research, most notably recent papers on the effects of soy/isoflavones on menstrual cycle length and isoflavone levels in infants fed soy formula. Their contributions, along with those from countless other scientists form the basis for much of the information reported in this newsletter.

Research Findings

Isoflavones and Arterial Compliance

An Australian study of perimenopausal and postmenopausal women found isoflavone ingestion (80 mg/day) in the form of pills improved systemic arterial compliance by 26 percent, an improvement similar to that reported for estrogen (2). However, LDL-cholesterol oxidation was not inhibited. Systemic arterial compliance is a measure of the elasticity of the main conduit arteries and is considered to be an independent risk factor for heart disease. Thus, even in people with normal cholesterol, soybean isoflavones may help to reduce heart disease risk.

Soy and Hot Flashes

One symptom experienced by many women going through menopause is hot flashes. It has been proposed that the weak estrogenic effects of isoflavones will help to relieve menopause symptoms. To test this hypothesis, Italian researchers fed two groups of postmenopausal women either 60 grams of a powder (40 g of protein) composed primarily of casein or a similar amount containing soy protein (3). The number of hot flashes decreased in both groups; however, over the 12 weeks of the study, the hot flash incidence decreased by 45 percent in the soy group and by only 30 percent in the placebo or casein group. Other symptoms of menopause, such as insomnia, headaches and depression were not affected by soy. The amount of isoflavones provided by the soy powder is the amount found in about two servings of traditional soyfoods like tofu and soymilk.

Daidzein and Immunity

Although most isoflavone research focuses on genistein, daidzein is also biologically active and there is almost as much daidzein in most soy products as there is genistein. Researchers from Tsinghua University in Beijing recently examined the effect of oral daidzein on immune function in mice (4). They found that daidzein stimulated phagocytic response of peritoneal macrophages and thymus weight in a dose-dependent manner. However, quite high doses of daidzein were used (20 and 40 mg/kg bw) compared with typical Asian intake (about 0.1-5 mg/kg), thus, it is not clear whether these effects in mice are likely to occur in humans eating soyfoods.

(1) N Engl J Med 1997; 337:1641.

(2) Arterioscler Thromb Vasc Biol 1997; 17:3392.

(3) Obstet Gynecol 1997; 91: 6.

(4) Nutr Cancer 1997; 29:1.

Reprinted with permission from The Soy Connection newsletter, Volume 6, No. 2, Spring 1998. More information about the newsletter can be obtained by writing to:

Editor, The Soy Connection
P.O. Box 237
Jefferson City, MO 65102

Isoflavone articles from The Soy Connection newsletter for registered dietitians, selected physicians and family and consumer science professionals...

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Copyright 1998
Indiana Soybean Board

 



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