Aromatase inhibitors are designed to inhibit the action of the enzyme aromatase, which converts androgens into estrogens by a process called aromatization. Aromatase inhibitors include Femara (letrozole), Arimidex (anastrozole), and Aromasin (exemestane). Aromatase inhibitors generally are used for estrogen receptor positive (ER+) breast cancer in postmenopausal women. Since the growth of ER+ (i.e., estrogen sensitive) breast cancer is promoted by estrogen, decreasing the production of estrogen in the body is designed to suppress recurrence. Note that whereas aromatase inhibitors block the production of estrogen, tamoxifen interferes with a tumor's ability to use estrogen.
There are some foods that also inhibit aromatase and other foods that increase aromatase or otherwise interfere with aromatase inhibitors. Please also see our article on the Impact of endocrine therapy on breast cancer prognosis on breast cancer prognosis.
Aromatase inhibitors normally are not used to treat breast cancer in premenopausal women unless accompanied by ovarian function suppression since inhibiting aromatase does not effect the production of estrogen by the ovaries (which is the most abundant source of estrogen in premenopausal women). To the extent that an aromatase inhibitor did decrease the production of estrogen in a premenopausal woman, the decrease would tend to stimulate the ovaries to increase androgen production, thereby neutralizing the effect of the aromatase inhibitor.
Weight gain after breast cancer diagnosis has been shown to increase hot flashes in breast cancer survivors on aromatase inhibitors. To varying degrees, women taking aromatase inhibitors also experience side effects such as an increase in joint disorders, an increase in the incidence of fractures, vaginal/urogenital atrophy, and high cholesterol (especially for those switching from tamoxifen). There are some foods that can reduce these side effects while at the same time reducing the risk of a breast cancer recurrence.

Foods that enhance the effectiveness of aromatase inhibitors

Foods, supplements and other to avoid while taking aromatase inhibitors

The following have been found to increase aromatase or reduce the effectiveness of aromatase inhibitors and should be limited or avoided during treatment:
Citrus peel
Corn oil
Goldenseal supplements
Grapefruit & grapefruit juice
Hesperetin or hesperidin supplements
Hormone replacement therapy, including bioidentical or natural hormones
I3C or DIM supplements
Peanut oil
Safflower oil
Soybean oil
Soybean paste
Soy protein isolate
St. John's Wort
Sunflower oil
Cigarette smoking has also been found to sharply reduce the effectiveness of treatment with aromatase inhibitors.

Foods that safely reduce the side effects of aromatase inhibitors

The following foods (or major components) have been shown to help reduce the side effects of aromatase inhibitors:
Arctic char - bone loss, joint pain
Black tea - bone loss
Blackberries - bone loss
Carrots - bone loss
Cherries, sour or tart - joint pain
Dry beans - bone loss
Ginger - joint pain
Green tea - bone loss
Herring - bone loss, joint pain
Kale - bone loss
Lake trout - bone loss, joint pain
Mackerel - bone loss, joint pain
Olive oil - bone loss, joint pain
Oranges - bone loss
Plums - bone loss
Pomegranate - bone loss, joint pain
Prunes - bone loss
Raspberries - joint pain
Salmon, wild - bone loss, joint pain
Sardines - bone loss, joint pain
Walnuts - bone loss, joint pain
While vitamin D might reduce joint pain and risk of fracture, one 2011 study reported that women taking vitamin D supplements during aromatase inhibitor treatment had higher circulating estrogen levels. The study results have not been replicated to date. However, it suggests that women should have their vitamin D levels tested and work with their oncologists to increase their levels, if needed, rather than taking high doses without supervision.
Aspirin appears to be safe to take during aromatase inhibitor treatment. Women should not use copper bracelets or copper compression garments to relieve arthritis pain. Copper has been shown to contribute to angiogenesis and metastasis of breast cancer.
Low-dose vaginal estrogen, which is used to relieve vaginal dryness and related urogenital atrophy, appears to be safe for use for postmenopausal women after aromatase inhibitor treatment has been completed.

Foods and beverages that might worsen the side effects of aromatase inhibitors

The following should be limited during aromatase inhibitor treatment since high consumption could contribute to bone loss:

Additional comments

We suggest that estrogen sensitive breast cancer patients and survivors to eat a wide variety of the foods from our recommended list and limit or avoid those on our avoid list, in addition to paying particular attention to the foods, spices and supplements on the lists above. Note that weight gain during aromatase inhibitor treatment has been found to be associated with less favorable prognosis. Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.
Below are links to recent studies on aromatase inhibitor treatment. For a more complete list of studies, please see the aromatase inhibitors tag.