Many people with breast cancer are told to avoid soy. However, doctors don’t recommend a specific diet for estrogen receptor (ER)-positive cancer. Instead, they advise avoiding foods that might interfere with medications or increase the risk of cancer growth.

In this article, we’ll discuss four foods you may choose to limit or avoid while living with ER-positive breast cancer. Your cancer specialist (oncologist) may recommend adjusting your diet based on your overall health and treatment plan.

1. Citrus Fruits

Oncologists often treat ER-positive breast cancer with tamoxifen, a medication that lowers the risk of the cancer spreading or coming back. However, certain citrus fruits, such as grapefruit and tangerines, may interfere with how well tamoxifen works.

If you’re taking tamoxifen, talk to your oncologist about citrus fruits. They can recommend how much of these fruits and juices are safe to include in your diet.

Food for Breast Cancer, a website that explores the connection between diet and breast cancer, notes that consuming large amounts of oranges or orange juice might also affect the medication’s effectiveness.

If you’re taking tamoxifen, talk to your oncologist about citrus fruits. They can recommend how much of these fruits and juices are safe to include in your diet. Your oncologist can also help you manage your tamoxifen treatment and side effects — including weight gain and dental problems.

2. Cow’s Milk

Cancer research suggests that cow’s milk may play a role in developing ER-positive breast cancer. Hormones and contaminants, like pesticides and nanoplastics (tiny plastic particles), found in cow’s milk may trigger ER-positive breast cancer in some people. Milk high in fat and saturated fat might also contribute to breast cancer.

Dairy is a key source of calcium, protein, and vitamin D. Health experts recommend dairy products as part of a healthy, balanced diet. If you have ER-positive breast cancer, you may want to limit drinking cow’s milk. Instead, try fermented dairy products like cheese or yogurt. Some research suggests that fermented dairy lowers breast cancer risk.

3. Some Supplements and Herbs

Studies show that some herbs and supplements interact with tamoxifen and other breast cancer treatments. Your doctor may recommend avoiding certain supplements to prevent toxicity and unwanted symptoms. Examples of herbs and supplements to limit while living with ER-positive breast cancer include:

• St. John’s wort
• Ginger
• Curcuma (turmeric)
• Ginseng

Your doctor may recommend avoiding certain supplements to prevent toxicity and unwanted symptoms.

No dietary supplements have been found to help treat or cure breast cancer. Doctors generally encourage people to get their nutrients from food, but they may recommend supplements for certain nutritional deficiencies. You should speak with your healthcare team before starting any supplements. These conversations help prevent unwanted drug interactions or potential harm.

4. Alcoholic Beverages

Evidence suggests that drinking alcohol is a risk factor for cancers, including ER-positive breast cancer. Alcohol can raise your estrogen levels, which ER-positive breast cancer cells use to grow and divide. It can also damage the DNA in cells, which provides instructions for how they grow and function. Changes or mutations in DNA from alcohol exposure may lead to breast cancer. Alcohol may also make tamoxifen less effective.

For your health, consider limiting your alcohol consumption or eliminating it from your diet. Try switching to mocktails made with fresh fruit and vegetable juices instead. Talk to your oncologist to see if your alcohol intake could interfere with your breast cancer treatment.

What’s the Deal With Soy?

There’s still some controversy and confusion about whether people with ER-positive breast cancer should avoid soy. This is because soy contains natural estrogen-like compounds called phytoestrogens.

Eating soy doesn’t affect your body’s natural estrogen. Some studies even show that eating soy products can lower the risk of breast cancer.

“I have been on a plant-based diet also since I was diagnosed. The only problem I find with vegan is most protein comes from soy-based products, and I have not been able to get a clear answer if soy raises estrogen levels or not,” said a MyBCTeam member.

Health experts from The University of Texas MD Anderson Cancer Center note that phytoestrogens are different from estrogen. Eating soy doesn’t affect your body’s natural estrogen. In fact, soy is a great protein source and an alternative to red meat.

Some studies even show that eating soy products can lower the risk of breast cancer. This is true in people with ER-positive breast cancer as well because soybeans contain antioxidants that limit inflammation and lower cancer risk.

If you’re looking to add more soy to your diet, be sure to get it from whole foods. Examples include:

• Tofu
• Edamame (soybeans)
• Soy milk
• Miso paste

Doctors usually don’t recommend soy supplements. For more information on soy foods in breast cancer, talk to your oncology team or a registered dietitian. Your healthcare team will help you manage your diet, treatment side effects, and other stressors while treating breast cancer and as a breast cancer survivor.

Talk With Others Who Understand

On MyBCTeam, the social network for people with breast cancer and their loved ones, more than 76,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Do you avoid specific foods because of your hormone receptor breast cancer diagnosis? How have the side effects of cancer and cancer treatment impacted your ability to maintain a healthy weight and consume a healthy diet? Share your experience in the comments below, or start a conversation by posting on your Activities page.