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.
To varying degrees, women taking aromatase inhibitors 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. Weight gain after breast cancer diagnosis has been shown to increase hot flashes in breast cancer survivors on aromatase inhibitors. While vitamin D might reduce joint pain and risk of fracture, preliminary reports suggest that taking vitamin D supplements could reduce the effectiveness of aromatase inhibitors in reducing circulating estrogen.
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:
Foods, supplements and medications 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:
- Corn oil
- Hormone replacement therapy, including bioidentical or natural hormones
- Safflower oil
- Soybean oil
- Soybean paste
- Soy protein isolate
- Sunflower oil
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:
Aspirin appears to be safe to take during aromatase inhibitor treatment.
Foods and beverages that might worsen the side effects of aromatase inhibitors
The following foods and beverages have been shown to have similar effects to the side effects of aromatase inhibitors and should be limited during treatment:
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.
Below are links to recent studies on this topic. For a more complete list of studies, please click on aromatase inhibitors.