Breast cancer is common; in fact, it accounts for one in every three cancers in females in the US and is the most common cancer in women, aside from skin cancer.¹ Most commonly diagnosed at age 62 and beyond, current statistics show that one in every eight females in the US will develop breast cancer at some point in their life.¹

Less than 10% of breast cancer cases are hereditary, and current evidence supports the fact that lifestyle plays a significant role in breast cancer risk and outcomes.^2,3 Factors that women can take action on include if overweight or obese, incorporating lifestyle and eating patterns associated with improved weight management, following evidence-based dietary guidelines for risk reduction and better outcomes for survivors, meeting advised physical activity levels, and assessing their alcohol intake.^1,4 Though no one food or dietary pattern can eliminate risk, there has been some exciting research in the past several years indicating that plant-based dietary patterns high in fiber from whole grains, beans and legumes, nuts and seeds, vegetables and fruits, and soy foods like tofu and edamame may help reduce the risk of death from breast cancer and breast cancer recurrence.^5-8 Despite the benefits of plant-based foods for people with breast cancer, questions about meeting nutrient needs, the safety of soy, and veganism are common. Healthcare providers should be armed with the latest research to provide evidence-based advice to their clients.

The Science of Plant-based Nutrition in Breast Cancer

Defining Plant-based Diets

For clients who are proactively incorporating plants in their diet, healthcare professionals can provide personalized care by asking what type of plant-based eating pattern their clients 

follow. Vegan diets are the most defined and exclude all animal products: eggs, dairy, fish, all meat, and most avoid honey. Vegetarian diets may or may not include dairy (lacto-vegetarian), eggs (ovo-vegetarian), and/or fish (pescatarian), so asking for clarification is critical.^8-10 Clients may use the term plant-based or flexitarian, which typically means a predominantly plant-based diet, but it’s essential to ask them how they define it personally.

Diets such as the Mediterranean Diet and Dietary Approaches to Stop Hypertension (DASH) are plant-forward (though not explicitly considered vegan or vegetarian) and have been linked to a lower risk of developing breast cancer. The standard Western dietary pattern is associated with increased risk.^2,4,10,11 A case-control study (n=1050) study by Rigi et al. used food frequency questionnaire data to index plant-based diets into quartiles (a common practice in diet and breast cancer research) depending on the amount of healthful plant-based foods commonly consumed. Women in the top quartile of a healthy plant-based diet (higher intakes of vegetables, fruits, legumes, and whole grains) had 67% lower odds of developing breast cancer than those in the lowest quartile (OR 0.64, 95% CI 0.43-0.94).² In another large study (n=65,574) by Shah et al. with a follow-up of 21 years found participants with high adherence to a healthful plant-based diet based on fruit, vegetables, nuts, and legumes had a lower risk of developing breast cancer compared to those with low adherence (consuming primarily refined/processed foods) [HRQ3 compared with Q1 (95% CI): 0.79 (0.71, 0.87) and HRQ4 compared with Q1 (95% CI): 0.78 (0.70, 0.86)].³

Just because a client defines their diet as plant-based doesn’t immediately indicate a dietary pattern associated with reduced risk for breast cancer. Intake of refined grains, sugar-sweetened beverages, or processed foods high in fat, starches, or sugars can contribute to excess caloric intake and increase the risk of overweight and obesity status, which is linked to many cancers, including breast cancer.^5,6,9 Assessing diet quality should be a first step for practitioners working with plant-based clients wishing to reduce their risk of breast cancer or recurrence. 

Mechanisms of Plant-Based Diets in Cancer Risk Reduction

Researchers hypothesize that the benefits to risk reduction, as well as reducing the risk of recurrence, are attributed to multiple factors in a plant-based diet, including higher intake of dietary fiber, micronutrients like vitamins C, E, folate, carotenoids, minerals like selenium, zinc, copper, and manganese, and phytonutrients such as phytoestrogens, phenolic acids, and lignans.^2,10,11 These nutrients may affect the gene expression of tumor suppressors in the body, support healthy DNA methylation (playing a role in gene expression and health), and affect cellular differentiation (the process where cells become specialized and take on individual characteristics, form, and function), the gut microbiome, and apoptosis (programmed cell death).^2,10 Following a whole-food, plant-forward diet provides antioxidants, anti-inflammatory, and anti-proliferative benefits (exerting effects that inhibit cellular proliferation) that may influence oxidative stress and DNA damage.^10,11

Evidence points to the fact that body weight is associated with both risk of developing breast cancer as well as recurrence rates. Guidelines advise following dietary patterns that support a non-overweight or obese status, and there is some evidence that plant-based diets can aid in that goal.^1,5,6 Vegan and plant-based diets are often lower in overall calories and are higher in fiber than other dietary patterns.^8,10

Following a plant-based diet also reduces exposure to known carcinogens such as N-nitroso compounds (formed during food preservation) and compounds such as heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) (formed during high-temperature cooking). Reducing red and processed meat intake may also reduce plasma levels of

trimethylamine-N-oxide (TMAO), a compound associated with some types of cancer, including breast.^9.10,12,13 The World Cancer Research Fund International (WCRF) recommendations for cancer prevention include eating no more than a moderate amount (no more than about three portions per week, which is equivalent to about 12–18 oz cooked weight) of red meat (beef, pork, lamb) and eating little, if any, processed meat.^6,14 

Crucial Nutrients and Considerations

Healthcare providers should assess all dietary patterns for nutrients that meet both macro and micro-nutrient needs, and plant-based diets are no exception. Studies show that plant-based diets are appropriate and safe for all stages of life, but it’s important to know that vegans need a reliable source of B12.⁸ 

Consider the following food sources to meet your client’s needs on a plant-based diet while focusing on the types of foods that may be cancer-protective:

Protein: legumes, soy products, nuts, seeds, and whole grains are critical sources of protein on a plant-based diet.⁸ Large meta-analyses (n=88 studies) and many clinical studies have shown that consuming soy isoflavones (genistein and daidzein) can reduce the risk of breast cancer in both pre- and post-menopausal women.^15,16 Higher consumption of soy post-breast cancer diagnosis is also associated with reduced death rates.^14,15

Omega-3 fatty acids: plant-based sources of anti-inflammatory omega-3 fatty acids α-linolenic acid (ALA) include walnuts, chia, flax, and hemp seeds.⁸ Some healthcare professionals may advise algae eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplementation for their vegetarian or vegan clients based on each person’s unique needs. 

Iron: lentils, white beans, kidney beans, tofu, spinach, cashews, pistachios, and even raisins can help plant-based clients meet their iron needs.^8,17

Calcium and Vitamin D: Studies show that lacto-ovo vegetarians typically meet their calcium needs, but vegans may be at risk of low intake.⁸ Fortified non-dairy milk and calcium-set tofu offer good absorption rates and high calcium levels to help plant-based clients meet their needs. Foods like white beans, almonds, figs, oranges, kale, bok choy, and turnip greens have lower bioavailability.⁸ Plant-based clients should also consider vitamin D-fortified foods or mushrooms treated with ultraviolet light to boost their dietary intake. Healthcare providers should assess a client’s intake and offer advice on appropriate supplementation based on each person’s unique needs and lab values, if possible.

Vitamin B12: Predominantly plant-based clients may also need to consider supplements, especially at age 50 and older when intrinsic factor (needed for B12 absorption) decrease.¹⁸

Takeaways for Healthcare Providers

While there’s no one food or one lifestyle change that can eliminate the risk of developing breast cancer (or contributing to the risk of recurrence in survivors), evidence shows that there are many modifiable lifestyle factors that women can take action on to reduce their risk. 

If a client asks a healthcare provider for advice on dietary changes, it’s important to use an evidence-based, personalized approach to educate on a healthful plant-based, vegan, or vegetarian diet that meets their needs. Use the AICR guidelines for the most up-to-date advice on diet and lifestyle support for reducing risk of breast cancer.⁶ Emphasizing fruit, vegetables, whole grains, legumes, nuts, seeds, and soy foods like tofu and edamame in addition to meeting physical activity guidelines (150 minutes of moderate-intensity activity per week or 75 minutes of vigorous activity plus two muscle-strengthening activities at least two days per week), and reducing or eliminating alcohol intake may help empower patients to make positive changes that could affect their long-term health.^1,4,5,6-7,19
References:

1. American Cancer Society. Breast Cancer. https://www.cancer.org/cancer/types/breast-cancer.html. Accessed September 1, 2024.
2. Rigi S, Mousavi SM, Benisi-Kohansal S, Azadbakht L, Esmaillzadeh A. The association between plant-based dietary patterns and risk of breast cancer: a case-control study. Scientific Reports. 2021;11(1):3391.
3. Shah S, Mahamat-Saleh Y, Ait-Hadad W, et al. Long-term adherence to healthful and unhealthful plant-based diets and breast cancer risk overall and by hormone receptor and histologic subtypes among postmenopausal females. The American Journal of Clinical Nutrition. 2023;117(3):467-76.
4. Khalifa A, Guijarro A, Nencioni A. Advances in Diet and Physical Activity in Breast Cancer Prevention and Treatment. Nutrients. 2024;16(14):2262.
5. American Institute for Cancer Research. Breast Cancer Research. https://www.aicr.org/resources/blog/new-breast-cancer-research-shows-importance-of-diet-and-exercise/. Published July 12, 2023. Accessed September 1, 2024. 
6. American Institute for Cancer Research. How to Prevent Cancer: 10 Recommendations. https://www.aicr.org/cancer-prevention/how-to-prevent-cancer/. Accessed September 3, 2024. 
7. Susan G Komen. Understanding Diet and Breast Cancer. https://www.komen.org/blog/dietandbcrisk/. Published Feb 26, 2024. Accessed September 1, 2024.
8. Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: vegetarian diets. Journal of the Academy of Nutrition and Dietetics. 2016;116(12):1970-80.
9. DeClercq V, Nearing JT, Sweeney E. Plant-based diets and cancer risk: what is the evidence?. Current nutrition reports. 2022 Jun;11(2):354-69.
10. Campbell TM, Campbell EK, Culakova E, et al. A whole-food, plant-based randomized controlled trial in metastatic breast cancer: weight, cardiometabolic, and hormonal outcomes. Breast Cancer Research and Treatment. 2024;205(2):257-66.
11. Romanos-Nanclares A, Willett WC, Rosner BA, et al. Healthful and unhealthful plant-based diets and risk of breast cancer in US women: results from the Nurses’ Health Studies. Cancer Epidemiology, Biomarkers & Prevention. 2021;30(10):1921-31.
12. Del Rio A, Parenti MD, Centonze D, Santoro A, Franceschi C. Extensive literature search on N‐nitroso compounds in food. EFSA Supporting Publications. 2022;19(10):7583E.
13. Chan CWH, Law BMH, Waye MMY, Chan JYW, So WKW, Chow KM. Trimethylamine-N-oxide as one hypothetical link for the relationship between intestinal microbiota and cancer – where we are and where shall we go?. J Cancer. 2019;10(23):5874–82.
14. World Cancer Research Fund International. https://www.wcrf.org/diet-activity-and-cancer/cancer-prevention-recommendations/limit-red-and-processed-meat/. Accessed September 14, 2024. 
15. Boutas I, Kontogeorgi A, Dimitrakakis C, Kalantaridou SN. Soy isoflavones and breast cancer risk: a meta-analysis. in vivo. 2022;36(2):556-62.
16. Okekunle AP, Gao J, Wu X, Feng R, Sun C. Higher dietary soy intake appears inversely related to breast cancer risk independent of estrogen receptor breast cancer phenotypes. Heliyon. 2020;6(7).
17. National Institutes of Health. Iron Health Processionals Fact Sheet. https://ods.od.nih.gov/factsheets/iron-healthprofessional/. Updated June 15, 2023. Accessed September 4, 2024. 
18. National Institutes of Health. B12 Health Processionals Fact Sheet. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Updated March 26, 2024. Accessed September 4, 2024. 
19. U.S. Department of Health and Human Services: (2018). Physical Activity Guidelines for Americans, 2nd edition. Accessed September 4, 2024.