A group of American women who took fish oil capsules for just three months experienced changes in breast tissue that may lower their risk of breast cancer, researchers say.

In an experiment at UCLA’s Jonsson Cancer Center, 25 U.S. women were put on a diet that mimics foods, including fish oil, eaten by Asian women who have a much lower rate of breast cancer than American women.

The results, said Dr. John Glaspy, suggests that the typical American diet, with its high content of vegetable and animal fat, may increase the risk of breast cancer, and that fish oil can quickly change the risk.

Glaspy cautioned that the study does not prove that a diet rich in fish oil would prevent breast cancer. A larger, longer study would be required for that, he said.

The study is to be published next week in the Journal of the National Cancer Institute.

Glaspy said that Asian women typically eat more fish, which is high in a fatty acid called omega-3. The American diet uses oils that are high in another fatty acid, omega-6.

“We know that omega-3 suppresses tumor growth in mice and in cultures, and that omega 6 promotes this growth,” Glaspy said in an interview. “And if you look at the body fat of women from low breast cancer rate countries, they have a higher omega-3 to omega-6 ratio. Also, women with breast cancer tend to have a lower ratio than do case controls (women without breast cancer).”

The researcher said his group conducted the experiment to see if the omega-3 ratio could be changed in the breast tissue of American women. Glaspy said the change occurred rapidly.