Women might reduce their risk of breast cancer by adopting a Japanese-style diet rich in fish oils, vegetables and soy products, researchers said Wednesday.
A study conducted at the University of California's Jonsson Cancer Center showed that the composition of women's breast tissue and plasma changed after three months on the altered diet. The findings will be published next week in the Journal of the National Cancer Institute.
Dr. John Glaspy, senior author of the study, said, "It's too early to make predictions, but we have absolute evidence that leads us to be optimistic."
He studied 25 women with breast cancer who adopted a diet heavy in soy products, fish oils and a variety of vegetables including green leafy vegetables, broccoli, Brussels sprouts, cauliflower and carrots. At the end of three months, the women experienced an increase in a certain kind of polyunsaturated fatty acids, shown to reduce breast cancer risk, and a drop in other fatty acids known to promote cancer.
Glaspy's study looked specifically at the results of the fish oil intake. Unlike omega-6 polyunsaturated fatty acids prevalent in American diets, the omega-3 fatty acids found in fish oils inhibit cancer. The women on the altered diet showed a fourfold increase in the ratio of omega-3 to omega-6 fatty acids in their plasma. The ratio, essentially a measure of good versus bad fatty acids, went up 1.4-fold in the women's breast tissue after three months on the diet.
Omega-6 fatty acids are found primarily in vegetable oils, shortening and other foods with high corn oil content, while omega-3's are found primarily in fish.
Glaspy said the study does not prove that a diet rich in fish oil would block breast cancer. That would require a much larger and longer experiment, he said.
Instead, he said the study show that by altering their diet, American women can develop an omega-3 ratio that is common among Asian women, who have smaller breast cancer rates.
The new research supports long-standing observations that women in Japan who follow traditional Japanese diets have a relatively low incidence of breast cancer. When those same women come to the United States and adopt Western diets, their frequency of breast cancer rises to that of American women within a single generation, the researchers said.