Mounting evidence suggests eating a diet rich in plant foods such as beans and soya cuts the risk of lung cancer.
Soya beans are a good source of phytoestrogens
The latest study involving more than 3,000 US people found those who ate more of these foods were less likely to develop lung cancer.
The protective effect, thought to be down to oestrogen-like compounds within the foods, appeared to reduce cancer risk by as much as 46%.
The research appears in the Journal of the American Medical Association.
The University of Texas Anderson Cancer Center researchers compared the diets of 1,674 lung cancer patients and 1,735 people of similar ages and sex who did not have lung cancer.
They used food frequency questionnaires to collect data on intake of 12 individual phytoestrogens - the plant-derived compounds believed to have oestrogenic properties and which have been shown to protect against some tumours in past studies.
The questionnaires had been completed before the cancer patients had been diagnosed with lung tumours.
Overall, the lung cancer patients tended to eat far less phytoestrogen-containing foods than those without cancer.
Phytoestrogens appeared to cut cancer risk between about 20% and 45% in men and women.
Scientists believe the oestrogen-like compounds act on receptors in the body, which regulate cancer growth.
"These data provide further support for the limited but growing epidemiologic evidence that oestrogen and phytoestrogens are associated with a decrease in risk of lung cancer," they said.
The findings back those of others who have noticed Asian populations who typically consume large quantities of phytoestrogens have lower rates of lung cancer than other populations.
However, the US team said more research was still needed to explore the link further.
FOODS CONTAINING PHYTOESTROGENS
Dr Kat Arney of Cancer Research UK said: "This research highlights the importance of a healthy diet in preventing cancer, and demonstrates the role that a person's lifestyle plays in the disease.
"Although this study is relatively small, it points towards the potential benefits of plant chemicals in preventing lung cancer.
"However, it is essential not to forget that nine out of 10 cases of lung cancer and a quarter of all cancer deaths are caused by smoking."
She said quitting smoking could significantly reduce a person's risk of cancer and other diseases, as could following a low fat diet, rich in fruit, vegetables and whole grains.