A new study has found soy foods aided the survival of women with an aggressive form of breast cancer.

Soy foods are not only good for breast cancer survivors but may even have a protective effect, a new study has found.

For a long time there has been confusion about the consumption of soy products among women because of the food's oestrogen-like properties.

The hormone oestrogen plays a role in both the development and growth of breast cancer in postmenopausal women and some research has suggested soy products may reduce the effectiveness of hormone therapies to treat breast cancer.

However, a study published in journal CANCER has shown this is not the case, and in fact the isoflavones found in soy foods slowed the progression of a particularly aggressive form of the disease known as hormone receptor-negative breast cancer.

Researchers at the Friedman School of Nutrition Science and Policy at Tufts University, led by Dr Fang Fang Zhang, looked at the relationship between the dietary intake of isoflavones and death from any cause in more than 6000 American and Canadian women diagnosed with breast cancer.

Over a median follow-up of nine years, women with breast cancer who consumed high amounts of isoflavones had a 21 per cent lower risk of dying than women who consumed low amounts.

This decrease was largely confined to women with hormone receptor-negative tumours and women who were not treated with anti-oestrogen therapy such as tamoxifen, which blocks the effects of oestrogen.

"Based on our results, we do not see a detrimental effect of soy food intake among women who were treated with endocrine therapy," said Dr Zhang.

"For women with hormone receptor-negative breast cancer, soy food products may potentially have a protective effect," Dr Zhang added.

Kathy Chapman, chair of the nutrition and physical activity committee at Cancer Council Australia, said the study findings were positive and cleared up the confusion about plant-based soy products.

But, she said, the "jury is still out" on soy supplements and women need to be cautious about these products.

"Soy foods are usually good for people to be consuming but the advice is not to take this study as meaning it's OK to for breast cancer survivors to take the large doses you would get in a soy supplement," she said.

Ms Chapman said breast cancer survivors need to focus on a healthy diet, maintaining a healthy weight and being physically active.