Susannah is World Cancer Research Fund's Senior Programme Manager (Research Evidence).
We’re often asked whether soya products affect a person’s risk of breast cancer, with many women unsure about whether it will increase or decrease risk. Information can often be confusing, making it difficult to know what to believe. The problem is that, to date, research just hasn't been able to confirm the risk either way.
Soya or soy?
Soya products come in many different forms, although they are all made from soya beans (also known as soybeans or immature green edamame beans).
They can be eaten whole or processed to make a number of different products such as soya milk, tofu and miso.
Our latest breast cancer report looked at the evidence on soya and found that, for women who have never had breast cancer, the evidence was inconclusive; four studies were identified which reviewed the evidence on soya and breast cancer risk, but none of the studies reported a significant association between soya products and risk of breast cancer.
This means the evidence on soya and breast cancer risk is limited and we are unable to draw any firm conclusions on whether it increases or decreases the risk of breast cancer. More research is needed to better understand the relationship.
We also reviewed the research on the impact of consuming soya for women who have breast cancer; we saw indications that consuming soya may be beneficial, but, once again, the evidence is limited so we can't make any recommendations at this time.
So should I eat soya or not?
Whole soya beans can be part of a healthy diet and contribute to your five-a-day. Soya is also a good source of protein making it a good alternative to red meat, too much of which increases your risk of bowel cancer.
However, if you do eat soya products such as soya milk, try to stick to unsweetened versions.
The bottom line
Until we have more research on soya and its link to breast cancer, we can’t make strong recommendations about its effect on cancer risk.
The evidence about soya may be inconclusive but there's lots of strong evidence about other things you can do to reduce your risk of cancer. Basing your diet on plant foods is a great first step to eating well.