Potential Risks of Isoflavones

Despite the epidemiological evidence for beneficial health effects of soy consumption, the safety of soy and its constituent isoflavones has been questioned. Concerns have mairrly arisen from animal and in vitro studies, but also a few human intervention studies relating to BC risk, which suggest that isoflavones may be involved in estrogen-sensitive cancer development, th5Toid dysfunction, and reduced fertility. 

Although isoflavones may be antieareinogenic, data from a limited number of intervention studies has generated concerns regarding increased risk of BC (Petrakis et al. 1996 McMichael-Phillips et al. 1998). However, data is limited and requires further investigation. Animal studies have shown conflicting results. Some studies have shown that GEN has a suppressive effect on chemically-induced tumors (Con-stantinou et al. 1996 Fritz et al. 1998), whereas other studies showed that GEN could stimulate the growtii of mammary implanted tumors (Hilakivi-Clarke et al. 1999). So far, there is no direct association between isoflavone eonsumption and increased risk of other cancer types. 

Results from several studies have raised speculations on the effect of isoflavones on thyroid function. Goitrogenic effects in infants fed soy-based IF were first reported in the 1960s due to increased loss of thyroxine from the gut and inhibition of thyroid peroxidase in the absence of iodine, a key enzyme in the production of thyroid hormone (Divi et al. 1997). The subsequent replacement of soy flour with SPI and supplementation of IF with iodine overcame the goitrogenic effects of soy-based IF (Merritt and Jenks 2004), and there are now no coneems regarding th Toid disease. Review of the literature suggests that there is little evidenee that thyroid function would be adversely affected by SF or SI supplementation in euthyroid, iodine-replete individuals (Messina 

LDL low density lipoprotein MCP-1 monocyte chemoattractant protein-1 MHF menopausal hot flashes NAF nipple aspirate fluid NO nitric oxide O-DMA O-desmethylangolensin OP osteoporosis PC prostate cancer PE phytoestrogens POST-M postmenopausal 

PPAR-y peroxisome proliferator-activated receptor y PRE-M premenopausal 

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