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. (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 latest research concerning the impact of endocrine treatment 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, 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

The following foods (or major bioactive components) have been found to inhibit aromatase or to enhance the effectiveness of aromatase inhibitors and are recommended during treatment:

Arugula
Beans, dry
Bell peppers
Blackberries
Blueberries & bilberries
Boysenberries
Broccoli & broccoli sprouts
Brussels sprouts
Butternut squash
Cabbage
Carrots
Cauliflower
Celery
Cherries, sour
Cilantro
Collard greens
Cranberries & ligonberries
Flaxseed & flaxseed oil, organic
Ginger
Grapes and grape juice, red

Horseradish & wasabi
Hot peppers
Kale
Mushrooms, white button & related
Mustard
Mustard greens
Olive oil, extra-virgin
Olives
Parsley
Pomegranates & pomegranate juice
Pumpkins
Raspberries
Rice, black, red or purple
Tomatoes
Turnip greens
Turnips
Walnuts & walnut oil
Watercress
Zucchini

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:

Alcohol
Corn oil
Daidzein
Genistein
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
Black tea - bone loss
Blackberries - bone loss
Carrots - bone loss
Cherries, sour - joint pain
Dry beans - bone loss
Green tea - bone loss
Herring - bone loss
Kale - bone loss
Lake trout - bone loss

Mackerel - bone loss
Olive oil - arthritis
Oranges - bone loss
Plums - bone loss
Pomegranate - arthritis, bone loss
Prunes - bone loss
Raspberries - arthritis
Salmon, wild - bone loss
Sardines - bone loss
Walnuts - bone loss

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.

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:

Chocolate
Coffee

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.