Aromatase inhibitors such as Arimidex (anastrozole), Femara (letrozole), and Aromasin (exemestane) suppress the production of estrogen within the body by inhibiting the action of the enzyme aromatase (which converts androgens into estrogens). There are also some foods that inhibit aromatase naturally (and others that increase it).
The growth of ER+ (i.e., estrogen sensitive) breast cancer is promoted by estrogen. Decreasing the production of estrogen with an aromatase inhibitor is designed to reduce recurrence. We cover foods that affect aromatase or influence the treatment effects of aromatase inhibitors in Foods to eat & avoid during aromatase inhibitor treatment.
Below we list only those foods known to inhibit or promote aromatase activity directly. The purpose is to provide useful information to postmenopausal women who would benefit from aromatase inhibitor treatment, but are unable to undergo it or other anti-estrogen treatment.

Foods that inhibit aromatase activity

Aspirin and metformin also have both been shown to inhibit aromatase expression.

Foods that increase aromatase activity

The following foods contain compounds that have been shown to increase aromatase activity, thereby increasing the production of estrogen. They should be limited or avoided by those with ER+ breast cancer.
Please see our article on aromatase inhibitors for more information.