Mushrooms contain a substance called conjugated linoleic acid that, according to recent research, appears to inhibit aromatase activity. Aromatase is an enzyme that helps the body make estrogen, so if there's less aromatase, there's less estrogen. Since many breast cancers depend on estrogen to grow, less estrogen may mean less breast cancer.
The same logic explains why aromatase inhibitors are used as adjuvant therapy (treatment after the main treatment) to prevent certain types of early breast cancer from coming back.
White button mushrooms were the focus of research, since they are the most commonly eaten type. Conjugated linoleic acid is also found in portobello, crimini, shiitake, and stuffing mushrooms. According to the study, 100 grams (3.5 ounces) or even less per day could prevent breast cancer growth and the benefit of conjugated linoleic acid appears to be gained whether the mushrooms are eaten raw or cooked.
Research on mushrooms has not yet been done in humans, but most dietitians agree that a diet rich in plant foods may be healthier than a diet that contains a lot of animal products. They also believe that the healthful compounds in different foods work together to provide health benefits. Instead of relying on a particular food in huge quantities, aim for a balanced diet with a variety of foods. And if you like mushrooms, include them as part of your overall diet plan in salads, sandwiches, soups, etc.