An article in a national newspaper recently sent out alarm signals about the use of soy products for women, in particular for those who have been diagnosed with breast cancer.

Soy is beneficial for many women, and used with caution and in moderation, but for women who are having treatment for breast cancer there is a definite problem.

Tamoxifen and soy

New advice is that women should not start eating soya products if they are on drugs such as Tamoxifen.

This is because the active ingredient in soy is genistein and this limits the effectiveness of some breast cancer treatments.

However this does not apply to women who have previously included soy as part of their regular diet. It is starting it at the same time as treatment that can be a problem.

Oestrogen and cancer

High doses of oestrogen have been linked to certain cancers, and ironically Tamoxifen is itself a weak oestrogen.

Soy is a phytoestrogen and its active compound, genistein, interferes with the actions of drugs used to treat breast cancer, including Tamoxifen.

Professor Leena Hilakivi-Clarke, of Georgetown Lombardi Comprehensive Cancer Centre, who conducted the research explained that timing of genistein intake is crucial.

‘Oestrogen drives most breast cancer growth, yet high soya intake among women in Asian countries has been linked to a breast cancer rate that is five times lower than Western women, who eat much less soya,’ she said.

So if your normal diet is already high in soya then there is no problem, but if you decide to switch your diet then experts warn that women shouldn’t start consuming soya milk or soy products after a breast cancer diagnosis – because it may limit the effectiveness of treatment.