NEW YORK (Reuters Health) - Eating a few ounces of mushrooms every day could help prevent breast cancer, a new study suggests.

"You don't need a strong effect to cause cancer prevention. Eating 100 grams or even less of mushrooms per day could have an effect on preventing new breast cancers," Dr. Shiuan Chen of the Beckman Research Institute of the City of Hope in Duarte, California, the study's lead author, said in a press release accompanying the study.

Extracts of the fungi interfere with the action of aromatase, an enzyme that helps the body make estrogen, the researchers explain in the medical journal Cancer Research. Most breast tumors require estrogen to grow.

Chen and her colleagues tested seven vegetable extracts for their aromatase-blocking activity, and found that white button mushroom had the strongest effect. The researchers evaluated 10 other types of mushrooms, and found stuffing mushrooms, portobello, crimini, shiitake and baby button mushrooms also inhibited aromatase activity.

Because white button mushrooms are the most commonly eaten type, the researchers tested extracts of the mushrooms in a series of laboratory and animal experiments.

The extract reduced the proliferation of breast cancer cells in a lab dish, while feeding the extract to mice implanted with breast cancer cells suppressed tumor growth, Chen and her team report. Further experiments showed that linoleic acid, a fatty acid usually found in meat and dairy products, was probably responsible for the extract's anti-cancer effects.

Based on the amount of extract used in the experiments in mice, about 100 grams of mushrooms daily would be enough to prevent breast cancer growth, Chen and her team state, adding that it is possible that eating even less every day could be effective.

"Results from this and other laboratories support the hypothesis that white button mushrooms may be an important dietary constituent for reducing the incidence of hormone-dependent breast cancer in women," they write. "Prevention strategies involving mushrooms are readily available, affordable, and acceptable to the general public."