Daily intake of isoflavones of >0.07 g associated with endometrial bleeding

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Authors’ Reply

Sir,

We appreciate the interest in our paper.1 We acknowledge that it would be useful for clinical practice and public health policy if recommendations could be made on the amount of soy food in the diet most likely to reduce the risk of endocrine-related gynaecological cancer. We agree with the comments regarding the dose-related effects of isoflavone on endometrial activity.2 However, it is the effect of soy extract, mainly isoflavone, that has been analysed in the studies quoted, not whole soy or soy foods. In contrast, the articles selected for our meta-analysis used the food frequency questionnaire (FFQ) to evaluate the effects of long-term intake of soy or soy foods, rather than of soy extract.3–7 Soy foods should be discriminated from soy extract in that they contain many other components in addition to isoflavone, and these unknown components may potentially affect endometrial activity and carcinogenesis. In addition, all selected subjects in five of the seven articles referred to were women aged 40 years or older with no menstrual periods for at least 1 year, or postmenopausal women, whereas our study analysed the effects of soy intake in women of various ages with or without normal periods. Although one of the problems with epidemiological studies analysing the diet as whole foods rather than as individual components is the inability to define the precise active principle, they do have the advantage of reflecting real life metabolic pathways, and also allow recommendations to be made for dietary changes involving routinely available foods rather than components which may need to be manufactured.

In conclusion, as pointed out by the authors, variable dosages of soy extract may exert diverse activities on the endometrium. It may therefore be necessary to determine the optimal amount of soy or soy food intake in further large-scale studies. However, this was beyond the remit of our study. Moreover, when interpreting our results, the differences between a soy-rich diet and the administration of soy extract should be taken into consideration.

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