Concerns about Soy Cultivation: What is Known and What is not Known

Abstract

There is abundant literature suggesting medical use for phytoestrogen-containing products. There is also published evidence suggesting potentially negative consequences of phytoestrogens use for humans. Substantiation of both concepts appears questionable. Meanwhile, soy products are used liberally in the food also for infants and children. The concept discussed here is that it is not consistent to support soy use for estrogenic effects without concern for its impact on routine use as a foodstuff and livestock fodder. It is important for thorough independent studies to be done to answer these questions. Phytoestrogens are substances of plant origin that are structurally and functionally similar to estrogens. Among them, isoflavones and coumestans are the most extensively studied groups. Isoflavones are present in different edible plants, but are most abundant in soy [1][2][3]. Consumption of soy products has been associated with favorable health effects, but potentially adverse effects are underacknowledged [4]. Phytoestrogens are advertised as a natural alternative to estrogens for hormone replacement therapy during menopause [1]. Preclinical trials have demonstrated both genomic and non-genomic action of phytoestrogens including selective but weak binding to the estrogen receptors [5]. Some epidemiological studies suggest that dietary intake of phytoestrogens may contribute to the decreased incidence of postmenopausal cardiovascular disease [6] and that phytoestrogens are significantly more effective than placebo in reducing the frequency of hot flashes [7]. Evidence in support of clinically relevant biological effects has been generally rated as insufficient or absent [5,[8][9][10][11][12][13][14]. A recent review concluded that in spite of increasing preclinical and clinical studies over the past decade, "appealing evidence is still lacking to support the overall positive risk-benefit profile of phytoestrogens" [15]. Then as now, the conventional menopausal hormone replacement therapy remains the only treatment that has consistently had a greater effect than placebo in controlled trials [16]. As evaluation of earlier works on enrichment the diet with soy products has failed to confirm favorable effects related to the cardiovascular system [17], doubts concerning phytoestrogens have recently increased. There is little evidence to support the hypothesis that phytoestrogens protect against menopausal osteoporosis, with published studies having no controls for confounding factors, the observations generally being of short duration [18,19]. In regard to osteoporosis, the latest review concluded that "evidence points to a lack of a protective role of soy isoflavones in the prevention of postmenopausal bone loss" [20], although in vitro and animal studies show some positive effect of isoflavones on bone which has not been clearly confirmed by long-term human trials [21]. There might be genetic differences in this regard, as equol producers seem to present a more positive response to isoflavone intervention ...