Radiation treatment (radiotherapy) can result in side effects such as fatigue, skin damage, and injury to the heart and lungs. A number of foods or their component molecules have been shown to relieve these adverse effects without lessening the treatment effects of radiation on breast cancer cells.
The foods listed below are recommended during radiation treatment. The list, which is updated continually as new research becomes available, has been developed based solely on the results of published academic studies. Clicking on any of the foods will take you to its webpage, which contains specific information concerning that food's relationship to breast cancer (including its overall ranking, for example, highly recommended or recommended in moderation), as well as links to supporting studies.

Foods that enhance the effectiveness of radiation treatment

The following foods are good sources of compounds that have been shown to increase the anti-cancer effects of radiation treatment and/or protect normal tissues (but not tumors) from radiation:
Tamoxifen has been shown to enhance the treatment effects of radiotherapy in ER+ breast cancer. Low-dose aspirin and the antidiabetic drug metformin have also been reported to increase the effectiveness of radiotherapy. In addition, research suggests that cholesterol-lowering drugs could result in less radiation resistance among hormone receptor positive (ER+/PR+) and inflammatory breast cancer (IBC) patients. There is also some evidence that limiting calories could heighten the treatment effects of radiation treatment.
Topical application of honey has been shown to be effective in reducing the severity of radiation-induced oral mucositis. Cigarette smoking during radiotherapy can result in increased treatment-related complications.

Foods that should be limited or avoided during radiation treatment

The foods listed below have been found to protect various types of cells against radiation (i.e., they are radioprotective) and are sometimes recommended for that reason to reduce radiation's harmful side effects. However, they should be limited or avoided since it is not clear whether they could interfere with radiotherapy (by protecting cancer cells from treatment).
Shellfish, especially raw shellfish, should also be avoided during radiotherapy because of the potential for foodborne illness that could interfere with the timely completion of treatment.

Supplements for patients being treated with radiotherapy

The following supplements have been found generally to be safe and beneficial for those being treated for breast cancer, including with radiation:
SupplementDosage
CoQ10 (if needed for heart health)100 to 400 mg/day
Fish oil (from wild-caught fish)1000 to 2000 mg/day
Vitamin D1000 to 2000 IU/day
Please consult your oncology team for advice concerning your specific situation and dosages. It might make sense to be tested for deficiency in vitamin D and plan for follow up testing to determine whether your reading has reached a desirable level.

Supplements that should not be used during radiotherapy

While antioxidants consumed in food might enhance the effectiveness of radiotherapy, use of antioxidant supplements during treatment has long been a source of controversy.

The case against antioxidant supplements

Radiation oncologists and others have expressed concern that antioxidants are capable of diminishing the effectiveness of radiotherapy by protecting tumor cells from radiation. This is because radiation destroys cancer cells in part by generating high levels of free radicals. Antioxidants have the potential to neutralize and nullify this mechanism of action.

The case for antioxidant supplements

Others have argued that antioxidants do not interfere with treatment and may, in fact, increase tumor response. Furthermore, some antioxidants can mitigate the adverse side effects of radiotherapy, thereby enabling patients to endure and complete the treatment. In addition, radiation reduces the level of antioxidants such as vitamin A, C, and E in tissues, which may need to be replenished. (However, this leaves the question of dosage for the most part unanswered.)

Bottom line

We do not intend to try to solve this question. High-quality academic research reports conflicting conclusions as to whether it is safe to take certain antioxidants and other supplements in combination with radiotherapy. However, it is clear that the circumstances that lead to tumor cell death are complex and that this complexity is too profound to be explained by relatively simple theories or clear-cut narratives.
Since research is in disagreement, we lean on the side of caution and recommend against taking the supplements listed below, which have been studied and reported in some (but not all, or even most) studies to reduce the effectiveness of radiotherapy:
We also caution against taking supplements of micronutrient such as apigenin, lycopene, or resveratrol that have been reported to be radioprotective or to increase radiosensitivity. This is because of the possibility of unintended outcomes, including breast cancer promotion. Safe and effective dosages for these supplements during radiation treatment have not been established; it is best to obtain these micronutrients through diet.
Please also see our article on how to optimize your breast cancer diet for more information on tailoring your diet according to treatment and breast cancer type and subtype.