A model to estimate the oestrogen receptor mediated effects from exposure to soy isoflavones in food.

The advantages that regular consumption of a diet containing soy may have on human health have been enshrined in a major health claim that has been approved by the Food and Drug Administration in the USA, regarding potential protection from heart disease by soy. This could have a major influence on the dietary consumption patterns of soy for consumers and lead to the development of soy enriched foods to enable consumers to achieve the benefits thought to be associated with increased soy consumption in a Western diet. If an increase in soy consumption is beneficial to particular disease conditions, there is always the possibility that there will be effects other than those that are desirable. For soy-containing foods there has been concern that the phytoestrogen content of soy, which is composed of several isoflavones, could be a separate health issue, due to the oestrogen-like activity of isoflavones. To address this, a method has been developed to estimate, relative to 17-beta oestradiol, the activity of the common isoflavones present in soy phytoestrogens, based on their binding to and transcriptional activation of the major oestrogen receptor sub-types alpha and beta. Using this approach, the additional oestrogen-like activity that would be expected from inclusion of soy supplemented foodstuffs in a Western diet, can be determined for different sub-populations, who may have different susceptibilities to the potential for the unwanted biological effects occurring with consumption of soy enriched foods. Because of the theoretical nature of this model, and the controversy over the nature of whether some of the oestrogen-like effects of phytoestrogens are adverse, the biological effects of soy isoflavones and their potential for adverse effects in man, is also reviewed. The question that is critical to the long term safe use of foods enriched in soy is, which observed biological effects in animal studies are likely to also occur in man and whether these would have an adverse effect on human health.