bean sprouts. Isoflavones are found primarily in soybeans and soy products and are
probably the best known and intensely investigated for their substantial health
benefits among the three classes. Lignans are found in many cereals and grains,
the highest amounts occurring inflaxseed. Despite their more widespread occurrence
in foods, and greater consumption in Western populations, the lignans have received
comparatively little attention. Although the number of studies supporting the health
benefits of lignans is growing, dietary consumption of lignans is plummeting.
According to 2002 data from the Framingham Heart Study, daily intake of lignans
by American women has dropped to less than 1 mg=day (Schatzman, 2007).
Evidence is beginning to accrue that phytoestrogens may offer protection against a
wide range of human conditions including breast, bowel, prostrate and other cancers,
cardiovascular disease, brain function, alcohol abuse, osteoporosis, and menopausal
symptoms (Bingham et al., 1998). The reported health benefits of the naturally
occurring isoflavones, genistein, and daidzein include relief of menopausal symptoms
(Murkies et al., 1998; Nestel et al., 1999), reduction of osteoporosis (Gennari et al.,
1998), improvement in blood cholesterol levels (Sharma, 1979), and lowering the risk
of certain hormone-related cancers (Peterson and Barnes, 1991) and coronary heart
disease (Federal Register, 1999). The basis for these effects has not been established,
but the weak estrogenic activity of isoflavones, sometimes referred to as phytoestro-
gens, may be a factor in conferring these properties. As a result, many food manufac-
tures are striving to provide products containing soy or isoflavones to consumers.
The interest in phytoestrogens as functional foods stems from research suggest-
ing that the intake of dietary phytoestrogens plays an important role in prevention of
menopause symptoms, osteoporosis, cancer and heart disease (Brandi, 1999), and
lung cancer (Schabath et al., 2005). Phytoestrogen supplementation withflaxseed or
soyflour has been reported to increase vaginal cell maturation, an indication of
estrogen activity in postmenopausal women (Wilcox et al., 1990), and significantly
reduce menopause symptom scores, particularly hotflash and vaginal dryness
(Brzezinski and Debi, 1999). Dietary studies indicate substantial reduction in breast
cancer risk among women with high urinary excretion of phytoestrogens, particu-
larly the isoflavone equol and the lignan enterolactone (Ingram et al., 1997). The
lower incidence of prostate cancer in Asian men compared to men from North
America and Europe has also been speculated to be due to the higher dietary intake
of isoflavones and lignans (Adlercreutz, 1990; Morton et al., 1997). A recent
preliminary study indicates that high isoflavone exposure is associated with low-
plasma estradiol in postmenopausal women suggesting the involvement of diet–gene
interactions (Low et al., 2005). Phytoestrogens may alter sex hormone and modulate
their metabolism at the cellular level by biochemical mechanisms. They influence
intracellular enzymes, protein synthesis, growth factor action, malignant cell prolif-
eration and differentiation, angiogenesis, calcium transport, Na
þ
=K
þ
ATPase, vas-
cular smooth muscle cells, and lipid oxidation (Adlercreutz, 1995; Adlercreutz and
Mazur, 1997). Lignans from the medicinal plantSchisandra, namely gomisin M
1,
even exhibit potent anti-HIV activity (Chen et al., 2006).
Isoflavonoid and lignan compounds exhibit a range of mammalian health-
promoting activities that are currently the focus of intense study (Table 1.1). Dietary
genistein reduces susceptibility to mammary cancer in rats (Fritz et al., 1998) and
Hurst/Methods of Analysis for Functional Foods and Nutraceuticals 7314_C001 Final Proof page 3 29.1.2008 2:12pm Compositor Name: VAmoudavally
Phytoestrogens 3