Women who eat foods such as fish and nuts during pregnancy may reduce the risk of their daughters developing breast cancer in later life, it has been claimed.

U.S. researchers said that mothers who ate foods rich in omega-3 fatty acids during pregnancy and while nursing, and then fed their babies such a diet after weaning, could cut the danger of future breast cancer in the youngsters.

In contrast, women who eat omega-6 fats — common in western diets including high levels of meat, eggs and vegetable oils — could be increasing their daughters' risk.

Dr. Elaine Hardman from Louisiana State University used pregnant mice bred with a genetic predisposition to develop breast cancer to see if the cancer occurred differently in the offspring if the mother was fed another diet.

All the mice exposed only to omega-6 in the womb, during nursing and after weaning, developed tumors by the age of six months.

However, less than 60% of the offspring exposed to high levels of omega-3 either maternally or after weaning formed tumors by eight months of age.

Hardman, presenting the research at the annual meeting of the American Association for Cancer Research, said suppression of tumor growth had been seen with as little as 2% omega-3 fatty acids in the diet. "A couple of servings a week may be enough.

"A quarter of a cup of walnuts constitutes one serving," the researcher said.