The benefit also came from other products from the soya plant, including soya fortified milk and dairy products.

However, diet in general had little impact on the disease, with dairy products, fruit and vegetables or tea not affecting the risk, added the study.

Scientists from the Northern California Cancer Centre carried out the research involving 100,000 active and retired teachers.

In total, 280 cases of ovarian cancer were diagnosed.

Each year, 6,000 women are diagnosed with the disease in the UK.

Claire Williamson, of the British Nutrition Foundation, said a small tofu-based meal or a drink of soya milk would provide 3mg of isoflavones.